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I have at Tesla system with 3 batteries, and I argued during installation to include 8kw of panels situated on the west side of our roof against Tesla ‘s engineering. The panels would only by 72% efficient on the west side as opposed to 74% on the east side (catching the morning sun). But my modeling showed that we would exhaust the batteries in the evening due to the fact that my usage was higher in the late afternoons and it wasn’t offset by any generation of solar panels during those late afternoon hours.

After modeling scenarios based on historical usage PER HOUR, I was able to show that if we had enough solar generation during peak late afternoon hours, we would be able to ‘survive the night’ on batteries until morning solar generation resumed. This means my 14kw solar panels coupled with 3 batteries gets me completely off grid for 9 months out of the year. That’s not bad considering I get 7ft of snow during winter months and I am surrounded by very tall trees.

Optimize on hourly generation not daily, most solar companies use DAILY numbers without a clue on hourly usage. I currently get 0.08$ for every 1$ in electric production, so there is very little benefit in producing electricity when you don’t use it. Optimize your system based on your usage not on DAILY production. If electric companies would give me credit of say 0.90$ per 1$ then the equation changes, but electric companies would rather benefit from your overproduction, be careful as these systems are not cheap!

This exactly. We run a 100KW microgrid on Hispaniola, and most of our panels are oriented to maximise winter afternoon sun, or just pointed randomly at the sky. Random pointing gets us more power than all oriented 12 degrees south because the power we care about is in overcast conditions, especially high altitude overcast, and that is variable in intensity in different sky regions on a minute by minute basis.

Also 12 degrees south would put a mountain partially in view of the panels, and mountains don’t provide much light here. (I don’t mean the mountains would block the sun, just a band of otherwise visible sky)

When we do have high intensity light, the late afternoon is when we want it, and also when the sun is most off to one side of the sky.

My advice: over panel as much as you can. We can fully charge our batteries while running the farm and 6houses in three hours of full sunlight, so we still get plenty on overcast days, and even on the few darkest days we make about 70%. We have to supplement the solar about 60 days a year total, burning a total of 300 gallons of fuel over the year for a small farm and 6 houses.

The Powerwall system prioritizes filling up the batteries first. I assume it will take pretty much your entire solar day to fill your three batteries so why didn’t you choose the model that fills up your buckets as the first priority? I think the rule is “optimize on hourly storage” and the hourly production should follow that requirement. Doesn’t the 74% give you a bigger area under the production curve than the 72%?

Bear in mind that charging and discharging batteries has an efficiency penalty - perhaps 98% efficient for each. So 74 stored is worse than 72 used directly because 74 -> 72.52 stored -> 71.06 discharged.

And usually the efficiency is much worse than 98%.

Oh, and also batteries such as the tesla power wall can only be charged and discharged about 1000 times before they have lost a lot of capacity. So generating when you use also makes your batteries last much longer. You could think of this as a cost of battery depreciation per kWh stored.

That 1000 is for NMC batteries and its a 70% capacity. Still enough to be useful.

Also, there's a lot of factors that go into play. For example, this assumes the batteries are fully charged and discharged. If you do something smarter like going down to 40% and up to 80% then they end up being able to do a lot more cycles. In fact, battery age starts mattering more than the cycles.

But besides that, LFP batteries are currently being used in home battery storage (including powerwalls) because it's cheaper and it has 5000->10,000 cycles before dropping to 70% capacity.

Generally, though, I'd agree that having more generation throughout the day is better than having perfectly optimized generation.

The Powerwall solar controller prioritizes the home before sending surplus to the grid. And in the home, the controller will send power direct to any running load first, then to the Powerwall battery. Any spillover then goes to the grid. It’s very dynamic. I would go with the algorithm to “capture the rain into my rain buckets the moment I can” because the rain could stop. Solar irradiance is unpredictable.

If you have time based billing you can also input that into the system and it's even more effective. For example, if you tell it that electricity is cheap from 9am - 5pm (peak solar) and expensive from 5pm - 9pm (peak residential demand) it will take your trending consumption and decide when your solar production isn't keeping up with foretasted demand and let you charge from the grid to at the cheap rate to make up the shortfall and minimize cost. It even factors in things like grid charging speed and total site usage limits, which are great given my 100amp panel.

The charging the battery from the grid on its own is interesting in spaces where the TOU between 4-7pm (or whatever yours is locally).

Here it is more than 3x, so if I can charge a battery and run off of that for those 3 hours, I am saving money.

And it's not that I can lose money, a charge in the battery doesn't become stale.

Don't forget to account for the additional battery wear from extra charging and discharging. However your cost saving probably exceeds the wear cost.

> Solar irradiance is unpredictable

Except in my case it is! I wanna do most of my charge at noon when I'll have far more than I can export. Export first, then charge!

That strategy make sense if you're goal is longevity for your first battery units. But with most early-adopter, often the attitude is to know you'll be upgrading somewhat frequently (3-5 years) due to rapid advances in the tech, until more advanced offerings come around that could least 10-20 years.

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Excuse what might be an ignorant question, but is the difference between 74% and 72% significant? At a big scale it certainly could be, but at the scale of a single family (or even small-ish multi-family) home I would think it wouldn't make a lot of difference, but I'd much appreciate a correction

I think the efficiency figure is the one the tesla engineers used. The one that he used is that he’d rather have optimal generation from 1-6pm than from 7-12am

> The Powerwall system prioritizes filling up the batteries first.

I think it depends on how you've configured it. My never charges the battery up from solar. I think it estimates how much power you'll need based on the configuration and charges accordingly. I've noticed on hot summer days mine will charge a bit in the morning then stop, then in the afternoon when the AC kicks on and off it will charge between AC cycles.

This is annoying approach. Mine is not Powerwall so I have to try to play with HAs scripts to only charge battery on excess solar - I have far more panels than I can export, and inverter (Deye) can only handle so much AC so excess DC needs to go into batteries.

Trouble is you don't really know how much excess power you've got until you crank up battery charge current.

We have a small roof with 1/3 of our panels facing east, 1/3 facing west, and 1/3 facing south. Given a sufficiently large roof, it would theoretically make sense to have all of the panels facing south.

However, due to the fact that PG&E keeps shifting our peak hours, we actually get more credit for producing in the afternoon, so when we expand our house, I'm planning on having all the panels (as much as possible) on the west-facing roof.

Also, we plan to install air conditioning at that time, so it will be helpful to be able to handle that peak demand.

> theoretically make sense to have all of the panels facing south

It depends what you are optimising for. East/west makes a lot of sense to optimise for morning and evening sun. Especially as during the middle of the day electricity prices usually drop due to excess solar.

There is no 1$ in electric production, unless you are selling and buying simultaneous at the exact same date and time, and from the same location. A fair price would be the current market price at the point in time, subtracted with the cost of operate transmission, facilitating the sale, and the predicted reduction in market price by increased supply. Depending on where you live the price difference between the average day of selling and average day of buying may very well be quite different. It is not uncommon in Europe to see negative market prices, where overproduction is not going to benefit the electric company at all.

> and I am surrounded by very tall trees.

https://www.suncalc.org works great for shade calculations, I was surprised when I checked tree shadows for different times a year.

Man your comment rings home so badly. Made a similar jump last year, and I was surprised we outperformed the predictions. Living in a cursed area (rainy + cloudy all the time), more than 50% of the year our electricity is 100% covered by our solar panel. 0 transportation (which is very high too).

It’s $0.08 for every $1 at retail rates, from the powerwalls, regardless of time or market prices?

Thank you for the example. I am always interested in real-life stories from other snow-laden users.

What do you use for heat?

I use both electric and Natural Gas heaters. Natural gas heaters are around 65/mo to run

Very tall trees, I presume.

Did you answer for A/C or is there a way to get heat from trees (without burning them)? (not a sarcastic question though I concede it probably sounds like it is)

Mostly agree, but there are also variables like feed in tariff (or delta between export and import) and mine just changed to 2 cents NZD. I've switched off hot water, battery and car charging scheduler because there is no point to save this anymore.

Plus modeling goes only so far when your behaviors change. I found it's incredibly hard to model this when there's so many variables.

Can your system work during a power outage? Most US installed ones up until about 5-10 years ago could not because they lack a proper automatic transfer switch certified to never back feed.

Yes, it’s one of the main reasons I purchased a system, I have had outages for longer than 2 weeks at a time .. PG&E

Storing energy from the summer for the winter is a really inefficient way to do it. It's much better to massively over-provision the solar so you have enough energy - on average - for the winter. Then you only need a couple of week's worth of storage to account for extended cloudy periods.

Much cheaper, and you get a ton of extra free power in the summer. The only downside is a typical house roof doesn't have enough space. But a typical house doesn't have enough space for a 1 MWh battery either so...

Yup if you really need to be off grid in a climate that has cold, cloudy, snowy winters, you’re probably going to need a generator that runs on fossil fuels. For everyone else, use the grid.

Agreed. You can increasingly over-provision the solar generation to reduce the proportion of time when you will need a fossil fuel generator or grid input, and install lots of battery to allow the system to smooth over multiple dull days. But chasing that 100% is going to be very expensive, and at some point it'll be much cheaper to have a fossil fuel generator that you need to run 1% of the time.

Yeah, w/o grid fallback, I’d much rather aim for 98-99% w/ solar and have an alternate source to close gap, rather than aim for “five 9s” on solar+batt. It’d take a lot to talk me out of a multi-source approach.

It's uncommon, but a wind generator can help a lot: in some climates, cloudy days tend to be windy days. Not really practical in a city though.

The AMC White Mountain huts have been doing this for years. The croo don't tend to maintain the systems, so I've never gotten a sense for what their storage capacity, generating capacity, and loads look like, but from a visitor perspective, the system works well.

Reportedly, even the fairy stout wind turbines they use up there have short, brutal lives. I heard the story of a croo that had to lasso/tangle/jam the blades of theirs in a storm because it lost the ability to control its speed and the alternative was letting it overspeed and possibly tear itself apart. They aren't large in diameter, but at the speeds they turn even in normal conditions up there, catastrophic failure could be really bad.

There's the passive haus highly insulated stuff. Guess that might work?

If you wanna spend 2-3x more, yes. Otherwise solar or grid battery is cheaper.

Try 30-50% more.

It's so obviously better to reduce your need for heating and cooling than it is to increase your panel. battery, and HVAC size.

30-50% over 500k build is 10x more than 10k solar or 5k worth of batteries.

I've just setup electrical heating for my bedroom (HA PID sensor). Uses about 450KWh - $90 NZD worth of grid power per winter. Heat pump would take 20+ years to pay itself. Double glazing probably 30-40 years.

To make same amount of solar power per year I need a single $130 NZD panel.

Wood burner is the best companion imho.

Or you find somewhere with terrain amenable to hydropower. It’s how we bridge the gap in the winter.

you have personal hydropower? that sounds pretty cool

A lot of great YouTube videos on personal hydro setups on small sized creeks. Even just a few hundred watts running 24/7/365 is an incredible resource.

And it's especially great if you have a neighbor with a son who are willing to do the labor for you. [1] [2]

[1] https://ludens.cl/paradise/turbine/turbine.html

[2] https://news.ycombinator.com/item?id=20075110

Or run it on biofuels.

Woodgas would work as well

I live off grid in inland northern California, and a have a solar panel array large enough to run my air conditioner continuously while the sun is up. It's just large enough to run the blower for a gas furnace in the winter so sizing turned out to be pretty even. Using a heat pump in the winter would require several times larger panel array, and running it at night would require the battery be much, much larger.

My 5 kW solar array and 24 kWh battery is fine for my 1300 sq ft house, all summer long, even when it's cloudy, and it works great for clear winter days, but as you mentioned for extended days of bad weather, the battery runs empty. Fluffy white summer clouds aren't a problem, but thick winter rain clouds let in so littl light that the whole array can't even run a 200 W refrigerator, so a few days of rainy weather depletes the battery and I have to top it off with a generator.

A 1 MWh battery isn't actually that big. There's electric trucks on the market right now with 600 kWh batteries sitting on the frame between the front and rear axle. That would easily fit into a basement room.

I wouldn't want a battery in my basement. if there is a fire in the battery your house will turn into a smoking hole, in the literal sense. Maybe if it was an iron-air battery or something safe, but not the current generation chemistry batteries.

" but not the current generation chemistry batteries."

Check for "Saltwaterbatteries", they are starting to reach consumer markets and literally cannot burn as the energy is stored as ... salt water.

Seems like the peak was around 2017 but they never performed particularly well?[1]

The problem is if the promise from the name was true, they'd be everywhere - they're not, so invariably much like vanadiun-redox or iron-flow batteries it turns out all the other details make them more expensive and less performant.

[1] https://en.m.wikipedia.org/wiki/Aquion_Energy

Yeah, I'm not saying it's a good idea. But you could do it if you wanted to.

LFP should be about as safe as other stuff people tend to store in their basements.

LFP's biggest issue is people aren't used to "Phenomenal Cosmic kW/h... itty bitty living space!" Yet.

That small? I was imagining burying a shipping container under the driveway/front yard or something.

Most grid-scale batteries that large will have bigger inverters (usually it'll be inverters that can dump that energy in 2-6 hours so 500-150 KW for 1 MWh of battery) and require cooling systems and such, but if you're putting that in your home then cooling will be negligible and the inverter will remain small. The batteries themselves are fairly compact, it's the support systems that get large.

What's the degradation cycle on batteries that size?

If you're using daily, do you get... three? five years?

Looks like - https://cartroubleshooters.com/how-long-does-a-tesla-home-ba... - ten to fifteen years with a guarantee of 10 years at 70% from Tesla

We're to the point calendar aging instead of cycles is the existential threat.

We can roughly estimate lithium ion batteries as 500 watt-hours per liter. Which makes a million watt-hours 2000 liters, which is two cubic meters. Add in extra overhead and it's still not all that much.

A good size comparison might by approximately the size of a stand up freezer, a common basement sight.

It's possible to store energy for full seasons, just not electricity.

It's been done with heat. Using cheap electricity in the summer to generate heat and store it in basalt. There's a small block of houses in The Netherlands that gets their heat that way: https://www.ecodorpboekel.nl/basaltaccu-is-opgebouwd-uit-duu...

There's more systems like this around the world, although they use different storage methods.

https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag...

Berlin just uses a really big thermos can to store heat: https://group.vattenfall.com/de/newsroom/pressemitteilungen/...

If you have good TOU rates (some even offer free) it's far cheaper to skip solar and just get a battery - they are options for less than $100 / KWh. That's $1.5k for battery + inverter + 1-2 hours of labour. Equivalent solar system can cost 10x that.

Do you have some suggestions for manufacturers? Thank you.

Tons on this channel https://www.youtube.com/@WillProwse

Off grid is silly unless you actually require it. Massive PV overprovision to ensure there's always something on the table is better than insane battery capacity. A couple of weeks worth of storage is a wild amount for a normal household.

I have a 22*980Ah 3.2Vn LiFePo4 array, and it holds a theoretical 13kWh at the 60% "safe" cycling rate (not below ~20%, not above ~80%, 3.0V min to 3.4V max). Taking DC->AC conversion losses into account, that ends up around 11kWh of 230VAC, which is enough for a single "normal" 24h period without generation: that doesn't include hoovering, welding, or running the dehydrator or dehumidifier. The batteries alone were USD$3500; BMS, balancer, cabling, etc. hundreds more. If I take $4000 as the unit price, then 14 days worth of power for us would represent $56k into a depreciating investment. I don't think most people are going to go for that. $56k would pay a lot of electric bills.

I'm in Ireland, which is fairly temperate, and we heat with wood (including the hot water). If you heat with electricity and you want to float that load on battery through a dim February...brutal.

EDIT: holy shitballs, that's $141,189.74 if you buy it as Powerwalls from Tesla rather than parts from Alibaba.

> $56k would pay a lot of electric bills.

In california, if you have AC and electric car that's 56 months.

EVs cost ~$2 to charge a day for an average amount of driving.

The cost for AC dwarfs the cost to charge an EV.

My bill was €316 bimonthly at €0.31/kWh before I put in panels. Last bill covering the two sunniest months I've ever seen in Western Europe was €100 exactly, of which in excess of €50 was the standing charge that is due regardless. The remaining ~€25/mo overage is the delta of our demand and the inverter's peak output. Next purchase will be more panels; another inverter would offer only marginal gains.

Huh, your numbers are weird. 22x980Ah of 3.2V cells would give you over 60kWh.

And the price of LiFePo4 continues dropping, it is not a good deal if your cells are aboe $80 per kWh (which at 22kWh should be below $2000).

Fuck. This is what I get for posting on 3 hours of sleep. My hallucinated bullshit came out so close to actual that it looked correct enough.

3.2v nominal per cell, 305Ah capacity: .976kWh per each. Call it .98. Not 980Ah, but 0.980 kWh.

.98 * 22 = 21.56kWh total pack cap.

*0.6 = 12.936 kWh available before conversion losses

We burn about 11kWh daily, so there's about a day in a full battery. Spring/mid summer worked well, but lately we aren't managing to store enough to get through the night, so I will probably add another 10 panels (5s2p) once I can find a grand I don't need.

I have a home in the southwest that is offgrid and runs entirely off solar. It has a 43kwh battery that covers 100% of it's needs including AC. It has a 4kw solar array.

The batteries shipped to your home inclusive of all taxes and fees, UL listed, are only $5,400 today from a variety of reputable suppliers.

This is obviously different than urban london but I wanted to point out just how economical this is for huge swaths of the country and how absolutely absurd some of the pricing I see on things like tesla powerwall are.

Note: There are a lot of components to an installed battery system that effect pricing such as racking, wires, busbars, breakers, etc, etc. I am referring only to the enclosed battery units with BMS.

The ratio between storage capacity and production power seems way too low, unless your daily consumption is ~10-15kWh and your batteries are over spec for harsh winter days (and then you’d need couple of sun days to recover). Are you sure about these numbers?

In it's location the solar is very effective, the 4kw is the actual generation rather than a label rating. 100% full sun, no shade, no clouds. The array typically generates over 20kw per day. The house is pretty efficient and the weather is very nice both summer and winter. This is not an area with a harsh winter or summer.

Shade and clouds of any kind, even very minor, have a HUGE effect on the production of a solar array.

London's latitude is north of Calgary.

I don't know how far south you are, but 15-20° of latitude has a significant impact on the effectiveness of solar, especially during winter.

Absolutely. Clouds also have a profound effect on solar output, I think much more than people realize. I am not english but my understanding is that london has a lot of clouds.

if you could tell me where I could get UL certified 43kWh battery for $5,400 I'd be very interested.

Ya, the OP is not telling the truth. One there isn't a "variety", second they aren't UL listed at that price. I've spent months researching this space for an off grid setup and these are the two best setups direct from China from a cost standpoint for 15 kWh. Neither are UL listed:

https://www.apexiummall.com/index.php?route=product/product&...

https://yixiangpower.com/products/yixiang-vertical-15kw-diy-...

Both would cost roughly $4800~$5500 for that total size.

If you want good customer service, dependable, UL listed, and correctly priced, then this is the king: https://signaturesolar.com/eg4-wallmount-indoor-battery-48v-...

UL listed ~45 kWh will cost you $10k, not $5.4k.

I don't know about 43kWH/5400$. But, here's the system I've been looking at:

https://www.expertpower.us/products/10800w-50kwh?_pos=2&_sid...

That's 50KWH of battery, plus the 10.8KW of solar, inverters, etc., all for $17K. That system is microgrid (not grid following) capable; so, you can run it during a blackout. The switchover is pretty good, too, so you don't need a second backup system.

I would definitely get EG4 over Expert Power for the reasons posted by other commentators.

Example kit:

https://signaturesolar.com/complete-off-grid-solar-kit-eg4-6...

Add in a 15 kWh module and it's roughly the same price with better customer service, reliability, less parts, etc.

However, I would just get an EG 18k PV, 45 kWh of EG5 batteries and 11.4 kW of solar panels from signature solar and that would cost you $18.5k

If I had to recommend in all in one kit, this september 2025, I would recommend an EG4 kit from Santan Solar. At brief glance they appear to be a stronger value and is from a company with a pretty strong customer service record. This is not sponsored in anyway.

It would be multiple batteries totaling that. Stock and prices are constantly changing but RUiXU, EG4 and EcoWorthy are widely available brands with UL listed options. Will Prowse's website has a page dedicated to code compliant batteries and there are several long lists and excel sheets on the diysolarforum.

I don't believe they are UL certified, but Dumfume sells 3.6kwh (300ah-12v) lifepo4 batteries for $320. 15 of those would get you 54kwh for <$5k. Might be tough to be anywhere near that point for UL certified only, though.

What are these batteries?

I did not name specifics because things are constantly changing in this market and these threads tend to live for years. Stock and prices are constantly changing but RUiXU, EG4 and EcoWorthy are widely available brands with UL listed options. Will Prowse's website has a page dedicated to code compliant batteries and there are several long lists and excel sheets on the diysolarforum.

Eco Worthy is not UL Listed and 45 kWh of RUiXU/EG4 is $10k+. Everything you've said is pretty spot on except for 45 kWh UL-listed batteries at $5,400.

> The batteries shipped to your home inclusive of all taxes and fees, UL listed, are only $5,400 today from a variety of reputable suppliers.

What about installation? DIY?

That is a much more complex topic driven by the regulations where you live. Where my house is, there is more or less no regulation and you can do as you please. In a purely technical sense there is not a lot of knowhow beyond basic electrical understanding, to setup these systems. Physically speaking these 280ah or larger battery setups are VERY heavy, hundreds of pounds per unit.

Do you have it in your garage or in a shed outside? I would be concerned about the fire chances.

It is in a utility room with some normal fire resistant features, walls are block and the electric inverters are mounted to cement board. The batteries cells themselves are in the steel cased battery boxes which help to limit potential fire risk. Very importantly these are lithium iron phosphate NOT lithium ion. There is still some fire risk with lifepo3 batteries but it is completely different than the thermal runaway possible with lithium iron.

The system I’m looking at costs twice as much for half the capacity. I’m very interested in what brand and model you speak of.

People seem to get really mad and accusatory over these sorts of things which is why I hate posting brands and such. The information changes very frequently as to what the "best" offer is. The diysolarforum is a very good resource to find the latest information.

It wouldn’t be that terrible to show dated proof with receipts. Inflation has probably jacked up the prices since you bought. Dating it would help.

If it's anything like my slice of the southwest, what works there may not work for a majority of Americans.

Even when it gets very hot in the day(100+), the nights almost always drop down to 63 or less. Meaning if you have a well sealed house you can suck up cold air during the night and ride it out in the day and have very low cooling costs. Coupled with low humidity from an arid environment means you can also let the house get hotter before it feels like it is time to turn on the AC.

This area has few days over 100 but does see relatively cool nights. It is an ideal area for this. I would say from southernmost california to southernmost texas, this basic setup is pretty workable and that includes something around 50 million americans. Regulator hurdles in some places make it impossible though. Costs are going to scale up mostly in line with the heating/cooling requirements and cloudiness of your area.

My panels are ground mounted and pointed in the ideal direction. I think this contributes to their efficiency because the ground helps cool them during the hottest periods but it is a tricky thing to nail down. On a previous home I had roof mounted panels and they seemed to perform much worse, difficult to identify the exact reason though.

how are you able to charge 43kwh on such a small array? we have a 12 kwh setup and it recharges a 15 kwh battery in a few hours.

In that part of southwest there are only a handful of cloudy days per year and at a relatively low latitude.

What’s the charging/discharge power of your battery? Is it AC or DC coupled?

My battery is 3 separate "48v" x 280ah units in parallel. There is no grid so I am not sure what you mean by coupled. The batteries output DC to inverters which output AC. It is several years old at this point, probably the better value is in "48v" x 320ah setups now. The breakers/busbars, etc are setup for max discharge of 200A but in practice I have never gotten anywhere near that.

The thing is LFP or Sodium ion are both expected to have 5000+ useful cycles soon (or possibly even in production now). This means even if you use one full discharge overnight , this is like 15+ years of life of the battery, although I suspect calendar degradation will be much faster.

Higher the cycle life, lower the levelised cost of storage and this is what matters in my opinion. Best is to have some type of long term storage like a Diesel generator only for estimated 1-2 weeks of the year depending on location where it will be needed.

I feel V2G with 3 days backup and a house low power mode which can be utilised in emergencies might solve even this issue.

Oversizing solar to the extent possible for winter loads is also ideal because so far that does not seem to be the driving cost.

> Best is to have some type of long term storage like a Diesel generator only for estimated 1-2 weeks of the year depending on location where it will be needed.

Unless you live in a location without much sunlight, it’s better to invest in a solar powered system with a transfer switch to go off grid.

If you size the system appropriately it can recharge the battery by day during an outage and now you can operate off-grid for a very long time.

Diesel generators come with maintenance overhead that adds up year over year. They also contribute nothing during normal times, as opposed to a solar install which can offset electricity costs or even earn money.

If you live somewhere dark this is less helpful, though.

Consumption also matters. Some people have eye-popping amounts of electricity consumption while other households get by with far less. The difference, including heating and cooling costs, is surprisingly large between the highest and lowest households.

>Diesel generators come with maintenance overhead that adds up year over year.

A good diesel generator is going to need very little maintenance operating few hundred hours per year.

Why do people talk about engines like they are unreliable? They are modern marvels.

I just replaced a residential condo building's fossil gas generator (Kohler 48RCLC), at a cost of ~$24k, because the association didn't perform the required maintenance on it. Yes, fossil generators can be reliable if you do the maintenance and you monitor to ensure they are doing a test run weekly/monthly under load. Lots of people don't.

My Powerwall quietly sits there charged and waiting to be under load, and charges to full when storm mode is activated (or I activate it manually). It has a 10 year warranty, 15 years if part of a virtual power plant (which my storage participates in with the local utility). It requires no maintenance. I also received a 30% federal tax credit for the Powerwall, which the building will not receive for a generator.

Diesel is not the same as a gas generator. There are a lot of things to go wrong with gas engines tbh. Diesel on the other hand will mostly run without too much fuss so long as there is compression and there is fuel.

Diesel lasts longer, but you should also be polishing the diesel fuel to keep it in good condition, which is another point of failure. When fossil gas is available, it is usually elected as the fuel of choice because this is unnecessary (as the generator is hooked up to gas pipelines, and no storage consideration is required). Propane will last forever in a proper container, but poses more storage risk than diesel.

TLDR Diesel generators where you might be without mains for a while and intend to replenish the fuel with deliveries during the outage, fossil gas for use cases where gas delivery pipelines are available (urban, suburban), propane for offgrid use cases (rural, cell towers, etc) where fuel longevity is a concern.

https://en.wikipedia.org/wiki/Fuel_polishing

if you dont have an ICE car, i think id prefer propane over gas? ill likely have the propane tank for a grill anyways

I think he is talking about natural gas rather than gasoline/petrol.

They are modern marvels indeed, but if you were to park your car in a field in May, by New Years when you go to start it up, it's a coin-flip whether or not it will.

Generators need to be exercised and maintained. You are committing to fire that thing up for a few hours every month, just to make sure it's in running order when you need it (I used to work next to a hospital that fired them every week).

For a modern car, If mice don't get into it and you have a battery maintainer, it's close to 100% going to start right up.

That fuel is probably going to be bad by then thanks to the ethanol that's put in it. Diesel is much more stable in that case.

I wonder if anyone has done any modern testing.

I had a 1990s car that started right up with 2015 fuel that sat in its tank for 9 months.

I had a car parked during covid and then remote work that probably consumed 1 tank of gas over the period of 2 years. Other than battery drain it was fine.

We have several large scale full building generators. Our exercise cycles are 15 minutes once a week. Our diesel mechanics fully service the engines every 3 to 6 months depending on size and importance.

Fuel is easy because we have an external tank with a visual gauge that you can read from several feet away. When they added DEF they neglected to add a DEF gauge that's as easy to read. Thank goodness they sell DEF at any old truck stop.

> Generators need to be exercised and maintained. You are committing to fire that thing up for a few hours every month, just to make sure it's in running order when you need it (I used to work next to a hospital that fired them every week).

This can easily be automated, Generac will handle testing for residential generators.

> operating few hundred hours per year

Do you really have a few hundred hours of power outage per year?

Around here, the power is so stable that we go multiple years without an outage that lasts longer than a few seconds.

If I installed a generator it wouldn’t a couple hundred hours per year. It wouldn’t run at all for years at a time unless I manually exercised it as yet another maintenance task for my already too long list of things to maintain.

You do need to run it at least once per quarter, though.

Unless you live in a location without much sunlight, it’s better to invest in a solar powered system with a transfer switch to go off grid

You're sadly describing my situation. Dec sees 6 hours of light, less even, and while the sun does get above the horizon, it doesn't get over the top of the forest.

(The trees have no leaves, but there's still a lot of tree trunks between me and sun.)

Bah.

> Best is to have some type of long term storage like a Diesel generator

LNG or propane would be far superior fuel types for long term standby generators. Periodically exercising a machine that runs on CH4 results in very minimal buildup on internal components. Liquid fuels are much dirtier and can also go bad.

Diesel is used in situations where you can afford all of the crazy maintenance. It's worth the trade off if you can.

The maintenance difference isn't that large. Diesel in a good tank also lasts an extremely long time, unlike gasoline. Diesel engines are more thermally efficient so you get more electricity per unit of fuel burned. The tanks don't need to be under pressure or replaced nearly as often as those for propane either. This is why most hospitals, data centers etc. that aren't near a natural gas line use diesel generators not propane. Natural gas has the benefit that when piped in, you don't need storage at all.

If you have access to ethanol-free fuel, that basically eliminates gasoline "going bad". It's the ethanol that degenerates over time.

I wouldn't say it "eliminates" it. Even without ethanol, gasoline still goes bad far faster than diesel. Gasoline is full of aromatic hydrocarbons that eventually will break down, and after a few years you're left with a brown stinky liquid.

Up until a year ago where I live, Chevron 94 Octane was ethanol free. I had issues with older carbureted engines after leaving gas in them for ~2 years. With E10 I wouldn't dare go that long as it can be so corrosive.

I can fill diesel tanks myself if need be.

I'm going to have a hell of a time with LPG.

There are dual-fuel generators, Ecoflow has a propane+gasoline option [1]. The problem with a pure propane setup is that propane doesn't really want to get gaseous if it's too cold outside - just like your cigarette lighter that you need to warm in your pants pocket before it can actually light a fire.

Diesel plus <any other kind of fuel> isn't available on cheap residential units I'm aware of, particularly as the ignition and fuel injection mechanisms are much more complex than a gasoline/propane mechanism.

[1] https://www.ecoflow.com/us/dual-fuel-smart-generator

No, LFP is 8k-12k cycles, and sodium are expect to be 15k to perhaps 20k cycles. This is reflected in the manufacturer warranties, and many sources. Here's one:

https://www.volts.wtf/p/whats-the-deal-with-sodium-ion-batte...

that makes calendar aging the limiting factor even more. I feel that so many cycles can also aid in smoothing solar & wind (at turbine level) output and increase their utility.

I feel that long term energy storage will be split between thermal and non thermal in interesting ways and the market for them will open up after first level of daily disruption

20,000 daily cycles if 55 years. 10,000 daily cycles is 27 years. The expected usage case for these batteries is near daily usage.

I hadn't really thought about thermal tech in such extreme terms until your comment, but to me it appears to be the tape storage of our times. There will always be a fair amount of infrastructure hidden that almost nobody knows about, but it's going to be dwarfed in active usage by HDDs or SDDs.

The tech advantages really are that big for batters and other solid state energy tech over the moving parts thermal variety. Thermal tech hasn't had an upgrade like LTO-6 (or is it 7 now) and is pretty much at the end of its possible engineered capabilities, but batteries are just barely getting started on what they are capable of.

The article here concludes with one year long cycle, of the 1MW battery.

Not without exception; there's some draw down after dinner even on the charge up sunny months. But a couple kWh against a 1MW pack is not super super notable. If it were cycle count alone degrading battery it'd still be an almost 5000 year battery (before becoming a 0.8MW battery).

As others are pointing out, we have stabilized chemistries even more, so 5k cycles is pretty low at this point.

If you just want to come out cost neutral, the battery required is far smaller when paired with a large enough array, and a time-of-use tariff.

With 3 EV's in the house, and a 12.8kWp array, with a 10kWh battery, charging overnight in the winter on the cheap EV tariff (7p per kWh vs 27p per kWh) and exporting during the spring, summer and autumn at 15p per kWh I'm seeing an electricity bill of below 0.

Of course, with a shift in energy production to renewables, all of that maths may get upended, but for now, I'm going to break even far before my original estimates.

> Of course, with a shift in energy production to renewables

clearly, you're not in the US as renewables are considered the problem here and not part of the solution. i'm waiting for the administration to come out with clawback plans for all of the subsidies for home solar and even the EV subsidies. gotta pay for those tax cuts some how

Politicians make a lot of noise about renewables but they're still being installed by grid operators record-breaking numbers, including in places like Texas.

Renewables pay for themselves and the lack of federal incentives no longer slows the rate they're being installed.

One of the most important new types of renewable, deep offshore wind, is just becoming very economical, and was on the precipice of being deployed at large scale in the US.

However, Trump has issued stop-work order on the only two projects, both multi-billion dollar, with issued permits. They are the ~800MW Empire Wind Project and the ~700MW Revolution Wind project:

https://www.utilitydive.com/news/trump-administration-offsho...

https://www.canarymedia.com/articles/offshore-wind/fishermen...

The Empire Wind project was allowed to continue after negotiation from NY's governor, but these sorts of mafia tactics will stop the development of new off shore wind projects. Multi-billion dollar projects getting shakedowns midway through is no way to run a country.

Perhaps even worse, it prevents the US form acquiring the construction skills to work on this on our own in the future. We are getting extremely far behind on a crucial technology for renewables at the population centers for northern latitudes.

> Perhaps even worse, it prevents the US form acquiring the construction skills to work on this on our own in the future. We are getting extremely far behind on a crucial technology for renewables at the population centers for northern latitudes.

nah, we'll just give out Halliburton style no bid contracts to companies owned by vice presidents. they've got plenty of practice pouring mediocre concrete pads underwater. at least when these let go, they won't spew oil

I was trying to work this out the other day and ended up building a thing because I couldn’t find anything similar from the energy companies: https://energybillcalculator.sensecall.co.uk/

That is quite a setup for the UK. I have gone for the frugal option, so that means I have a vehicle fleet that consists of one naturally aspirated bicycle augmented by electric train for longer journeys. In Scotland the trains run with electricity from wind farms, so I am okay with that.

However, from how you describe it, you are getting lower costs than me! My electricity bill is lower than the standing charge, but this adds up to more than what you are paying. Train fares also seem to be costing me more, although I have done well out of compensation for late trains recently, so my trips to the south of England are averaging out at around £100 for the return journey.

I am beginning to question my life choices. Frugal was the wrong way to go. Why do I need this cardiovascular exertion when I could be getting around for less in a two-tonne EV?

I think I missed the boat. Getting a feed in tariff is far from given these days and the government grants for solar ended about a decade ago.

You still don't pay VAT if installed by an MCS accreddited installer.

Also commute by train, and yeah, it's not cheap. My season ticket is £11k a year!

It's an interesting thought exercise, but the quick short term solution would be a 5kWh buffer battery just for the evenings to save buying at peak times.

I started that way before going fully off-grid to avoid subsidising the fossil fuel industry here. Plus ~70% of my bill was fixed charges, and they wouldnt pay for excess solar generation above what I used.

I think this sort of mega home battery bomb could be avoided through legislation by offering free grid connections. So I 'pay-in' 10kWh today, and maybe my account is credited with '5kWh' for later use. I'm sure we would see a much bigger uptake of home solar with such a scheme.

10kWh during periods where the energy market price is at the lowest will not pay for 5kWh for periods where the price is at the highest. It will be closer to 0.1-1 kWh for every 10 kWh.

The alternative (the current model where I live) is to have the government be responsible for grid stability, in which they will add taxes and fixed grid connection fees to pay for that service. Crediting overproduction won't make the costs lower for the government, so any such credits will just be a form of subsidy.

I'm happy to sell my solar power at night.

A couple buffer batteries in each home should eventually help even out pricing with everyone trying to sell during peak demand times. But yeah, grid stability might be a fun challenge.

Suburban homes capable of overproducing power also have by far the highest per user grid maintenance costs due to simple distance. I agree you would see an uptick in solar adoption with your scheme, but only because apartment-dwellers are being conscripted to subsidize your grid connection.

Early subsidy plans were short sighted and came from politicians, not grid operators, and gave homeowners a massively inflated sense of the usefulness of the meager kWh they produce. Power is cheap, infrastructure is not. It's far better deal for the commons if you use all the kWh you produce (via storage) and pay what it costs to deliver a grid connection when you fall short.

Look up "net metering" or NEM, this is already a thing in many jurisdictions.

Yes. (In India) we recently converted our SFH into a 4 storey building. We were forced by building code to

A) add solar panels covering 1/3rd of the terrace

B) use it for all non-floor-space electricity (lifts, common areas, pumps, parking lots)

C) Give the rest for deductions as part of NEM.

Once we move in, I'm interested to see the tariff for the export and how much it will save us.

And in many jurisdictions they're putting time limits or just straight up eliminating net metering and replacing it with net billing.

So instead of 1:1 credits, the power company buys it from you at what they would pay their producers (read, several times less than what they charge you).

It's a fucking scam.

My power company limits the size of panels and time limits net metering (they don't even do it anymore for new solar installs). So you can either not do solar or go completely 100% off grid with only one step.

It's a fucking scam. The engineer justified it to us when he was signing off on our solar install as "well when we do 1:1 credits c that's like you stealing from your neighbors. They don't want to pay your the full retail cost. They want to pay you what we pay the power producers."

When I asked if that meant my neighbors would have the ability to pay less, he just sort of looked flatly at me.

An absolute scam.

Edit;

Sorry, I forgot to add;

1. They also won't allow battery storage while connected to the grid. If they wanted to buy surplus but allowed my to store my own production, I would be fine with it.

2. They also net bill daily. So while I may produce extra within the billing cycle, they zero out excess production daily.

Well, in some cases it's scam, but its genuinely the case that power at different times of the day has different value, and most NEM agreements completely ignore the cost of transmission, which itself is quite hefty.

So it is plenty reasonable that you wouldn't get 1:1, especially if the grid is already able to satisfy all demand during peak sunlight by using just base load + solar. Some power companies turn it into a scam anyway and set grossly disadvantaged prices for consumers, but just because it's not 1:1 doesn't mean that it is a scam.

Well, infrastructure costs money.

But talking about the cost of transmission sure does highlight issues with this billing model. Because if it's going to the neighbor there's negligible transmission. The engineer's argument was very stupid.

The energy market has many similarities to the stock market. People also bet on the prices going down or up by contracting themselves to produce a set amount of energy at a given time for a given price. There are companies which only do trades and has no own production, earning their profits only through market predictions.

isn't it logical though that the power company would buy power for less than it sells? and paying the same rate that it buys from larger producers seems fair.

Sorry, I forgot to add;

1. They also won't allow battery storage while connected to the grid. If they wanted to buy surplus but allowed my to store my own production, I would be fine with it.

2. They also net bill daily. So while I may produce extra within the billing cycle, they zero out excess production daily.

The principle is fair, but the specific price can be unfair. Especially if the home as provider could be supplying into spot or other markets. Thats where a neighborhood or coty consortium/ cooperative of community users could make sense to maintain a better pricing deal from the utility.

Can't shake the feeling that domestic PV is a con designed to try and shift responsibility for the climate crisis to consumers rather than industrial energy providers.

The ROI of a large PV farm must be substantially better than a home scale install.

>The ROI of a large PV farm must be substantially better than a home scale install.

There are many benefits to letting homeowners do it. First of all you get a lot more solar deployed in much shorter time, because you mobilize hundreds of thousands of people to the effort immediately instead of having them wait for a solar plant. Homeowners pay for it, provide the area for it, hire and organize the workforce - small scale but "everywhere at once" so to speak.

The government/state/county doesn't need to wait for the land to be available, raise the money, build infrastructure to transfer electricity from a new large solar site to the consumers and so on. So for the "state" the ROI is better with home installs.

>responsibility for the climate crisis to consumers rather than industrial energy providers.

That's where the responsibility belongs through. Most of us drove fossil fuel cars for years, which is the largest single emission source. In democracies we could have voted for guys wanting gas to cost 50 bucks per gallon, or who would prohibit any more oil and gas to be traded. We didn't. We could have refused to travel for vacations, refused to buy goods shipped from overseas and so on - but we didn't. So this is on us.

This mostly seems to support my statement that the ROI is worse. You cannot discount the cost of the house entirely in the equation. Many people are not even home owners.

You may be right about the ROI in a strict sense, I just question why it matters.

A communal solar farm is not the same product as personal home solar anyway. When someone with surplus money decides to pay for their own solar it might be suboptimal ROI for them, but the rest of us get a little bit of solar benefits for 0 money.

And more importantly, solar starts replacing fossil fuels rightaway. No waiting for a communal, optimal ROI initiative to get started.

But of course, we should do those as well.

> In democracies we could have voted for guys wanting gas to cost 50 bucks per gallon... So this is on us

Only kind of. The oil companies dusted off the old tobacco playbook. Democracies are unfortunately terribly vulnerable to well-funded liars.

Approximately 0% of voters vote to ban fossil fuel use in cars overnight (some want to phase it out over a decade or two). So do you think it's too late and voters rationally don't want to anymore, or that almost every voter is still believing lies promoted by oil companies? What are the lies?

Check out your grid bill and you'll probably see that cost of the grid is higher than the cost of the generation.

Local solar requires far less grid, and expanding the grid is one of the greatest (political, not technical) challenges of this era in the US.

Unless you're accounting for the grid costs, the "cost" of utility vs. rooftop is not an apples-to-apples comparison.

As far as a "con" the only con is that the costs in the US for rooftop solar are multiples higher of other places, like Australia. That's the con. Australia also shows that rooftop solar is great for grid in general, greatly driving down costs.

Of course, rooftop solar is terrible for utilities, so you are going to encounter tons of astroturf denouncing it all over the web, and even face to face. Utilities are fundamentally threatened by consumres taking over more and more of their own electricity responsibility, especially as batteries get super cheap.

The problem is when there are long stretches of little to no power generation. Fully covering those gaps with batteries would require very large (and costly) storage. During this time the grid needs to be large enough to support everyone, just the same as if solar did not exist. You can say it's terrible for utilities, but at the end of the day they will have to pass the cost of maintaining the grid along to non-solar customers.

What do you mean by long stretches? Are you talking about sundown to sunset?

In many (most?) areas, wind picks up at night, wind can't really be "local", and demand is lower at night time so that's a great use for the grid.

Also, batteries are getting so cheap that people are putting multiple days' worth of storage on wheels, driving them around, and parking them at home during the evening peak and overnight.

When they are that cheap, adding 10-20 kWh of local storage is going to pay for itself in no time.

When my neighbor is overproducing solar during the day, that means that he's sending his power over to my house, which doesn't have solar. Which means that my neighborhood is pulling down less peak power. And the grid is sized for peak power, not for minimal power, so whenever that peak is lowered, it saves me money but costs the utility profits.

Because the utility gets to recoup a fixed profit rate off of any amount of grid they are allowed by the PUC to install, whether it was needed or not. My neighbor, with the solar, also pays lots of fees for the privilege of sending me power and requiring less grid.

This effect of shaving the peak is so extreme that solar causes the California duck curve. Though the storage that's been added in just the past two years has pretty much solved any problems needed for the evening ramp as the sun goes down, now.

It's only the highest peak that matters. During periods of Dunkelflaute[1], batteries will run dry and the grid will need to support everyone.

[1] https://en.wikipedia.org/wiki/Dunkelflaute

Seems like a great time and place for the iron air batteries that are getting deployed now (Form Energy). Even in the US, without Dunkelflaute, these 100:1 energy:power batteries are economical and paying for themselves on the grid. If there are several of these occasions per year it could be a great fit.

It also seems likely that HVDC from sunnier areas like Spain or maybe even Morocco could be cheap enough. I'd recommend nuclear but EDF is having such great difficulty building it. HVDC and other exotic solutions like enhanced geothermal seem for more practical at the moment.

Do you ever actually converse with people or do you just DDoS them with random information. I made one simple point and you have not addressed it.

HVDC, long-duration batteries, and enhanced geothermal directly address your concern. And if they do not, you have not bothered to express your concern clearly.

You’ve shifted to promoting renewables. That wasn’t the point. The point was cost-shift: rooftop customers still use the grid but avoid paying for fixed T&D. Address that.

> The problem is when there are long stretches of little to no power generation. Fully covering those gaps with batteries would require very large (and costly) storage.

Perhaps local solar installations could be incentivized to include their own smaller scale storage...

California has done this with their latest version of net metering for residenial solar, NEM 3.

It makes solar a very financially unattractive option unless there's storage attached to the system, and has drastically reduced the rate of residential solar deployment.

NEM3 was justified under the proposition that lower-income households were "funding" the higher income households to get solar. So as solar finally gets cheap enough for the lower income households, they changed the rules again so that only those rich enough to afford batteries and solar can save money.

NEM3 has a few nice things about it when looked at narrowly, but overall seems pretty disastrous for the state.

Disastrous is an oversimplification you can only make if you don't understand the broader context. Grid stability is more important than some homeowners saving some money, it turns out those extra kWh being dumped onto the grid were literally costing the operator money to deal with. Those costs got passed on to _other_ consumers because of the sweetheart deal.

Residential solar installs are way down, that's correct, residential isn't the only venue for solar, and within residential storage capacity is skyrocketing and it's already having a measurable effect on the early evening peak. Lower peaks means less capacity needs to be built just to handle a few hours. This is good.

The unequivocally negative impact I don't have an answer for is the job losses for solar installers.

> Grid stability is more important than some homeowners saving some money, it turns out those extra kWh being dumped onto the grid were literally costing the operator money to deal with. Those costs got passed on to _other_ consumers because of the sweetheart deal.

If that was the concern they literally did nothing to stop it. Instead of dealing with backfeeding from a distribution station, they went entirely the other direction.

Those grid costs, if they actually existed, were in isolated areas with high levels of solar, and NEM3 will continue deployments of solar in exactly those areas.

Solar is not "savings for some homeowners" it's literally keeping grid costs down for everyone, keeping our grid reliable on the hottest hardest to run days.

It sounds like you are alluding to NEM3 here. If so, I'm not sure that was meant to incentivize small scale energy storage. They recently tried to implement a flat fee that would have killed residential solar entirely, even with batteries. That did not happen, but I think it shows the motivations. I'm also not sure batteries even change that much for the grid. You still need to have the capacity for lulls when all the batteries are empty.

Rooftop solar doesn't require additional land to be purchased, reduces the need for more transmission lines, and reduces transmission losses. I don't know how big these all are but it seems plausible they make it a better deal than industrial solar.

Batteries on the other hand feel like they take less space and thus could be colocated near consumption without having to be on consumer property. Warehouse size within the city. Transmission costs would be minimal.

It doesn't do any of these things.

I can't put PV on my neighbours house, I have to buy land to put it on. My home still needs a grid connection so all that infrastructure still needs to exist. Except now it's even more complex.

PV and energy generation in general benefits massively from economies of scale. Home generation doesn't have that.

The obvious point is that roofs have been built unnecessarily strong for decades.

Unnecessarily strong? 2kW of solar weighs about the same as one roofer.

If your roof can't hold up solar, it also can't hold up the people that need to work on it.

Because they can carry solar panels?

Roofs have to handle several tons of wind pressure, snow, people walking on them and so on. They can handle solar panels no problem - which is why it's such a good idea to put solar panels on them.

The answer is do both, industrial utility PV has so far been lower cost, but individual PV is higher resilience - especially in the age of extreme weather events.

I have a grid detachable PV system with battery. It's been invaluable for grid blackouts in my area to have the capability even as I have paid (at least for the first couple years) a higher price per kwh for it. Over more years, it's really nice to have price insulation against utility price increase.

It's the best kind of revolution: one that doesn't need permission from gatekeepers. At least not anymore.

Don't underestimate the value of decentralization in some scenarios.

It's still pretty amusing to regard this as "decentralized" when solar panels are produced in a centralized fashion. This is just changing who is buying things, not something fundemental.

CPU production is centralized, but email is decentralized. Email changed a lot about the distribution of information without necessarily changing the distribution of industrial manufacturing. Likewise solar will change the distribution of energy without necessarily changing the distribution of industrial manufacturing.

Once the panel arrives at your home it keeps making electricity for decades, without asking anyone's permission.

Email is decentralised if you ignore that 99% of email must go through the gatekeepers known as Microsoft and Google. Sure, anyone can spin up an email server, but either one of the gatekeepers can arbitrarily decide to reject all email coming from your small server and there is no recourse beyond begging them to reconsider.

The real infrastructure is the backbone providers and telecom companies. You can't do anything without them.

It is true that once they are installed after making a consumer choice, you will be more resilient, so I should concede it is a real difference, but nonetheless, it's control of production that still controls the entire ecosystem. In the case of utilities, control of production is felt instantaneously whereas with solar the lag is years.

If one can offset your electricity bill by more the cost of the install and come out financially ahead then that is compelling to the individual, I doubt many people are knowingly eating a loss and stumping thousands upfront solely because they think they are helping the environment

Well, solar salesmen can be pretty slimy, hiding costs left and right. That said, the monopoly utility grids have a chokehold on power, and escaping that monopoly is often worth the 2-5x premium you are going to have to pay vs a utility scale project.

Plus, when people compare the cost of home solar vs utility solar, they often ignore all of the infrastructure (especially last mile infrastructure) that's needed to get the power from the utility scale solar farm to someone's house.

If you live somewhere with expensive electricity and decent sun (California, New Mexico, Arizona, Florida, the Carolinas, etc) it's usually worthwhile to put solar on your home. It's less effective than if someone competent were to spend the same money improving the grid, but in this day and age that's a lot to ask.

I think most people installing solar are doing it in the hopes of improving their property value while possibly buffering their total dependence on the grid, with environmental virtue as a secondary benefit.

Yes and no. Having your own electricity production shields you somewhat from rising energy prices. That added predictability is worth something.

It depends. 80% of my electricity cost is taxes. If I produce it using PV, the consumption is never taxed, and the benefit is pretty substantial, on top of the market electricity price. (One rarely finds low risk investments that return 20-25% year)

Curious where you are roughly located; Does that 80% include the distribution of the electricity?

Should I interpret the 20-25% returns as being, your annual savings on the utility bill are 20-25% of the cost of your PV install?

Netherlands. No distribution fees are separate.

Roughly speaking the electricity is about €0.06 with about €0.20 in taxes on top. So offsetting consumption nets me about €0.26 cents per kWh.

The installation of a 2800kWp system cost me about €2600 and generates between 2400-2750kWh annually, so about €650 euro. In a 10 year timespan that’s an IRR of 20%, creeping up to 25% for 20 years.

Thanks for the numbers! I had no idea taxes were such a large fraction elsewhere. Good to know/consider. I'm most familiar with California. (and actually can't give a % that is taxes offhand)

After the first year of having PV, I determined my own payoff time of about 5-7 years, so that was nice and self-justifying, and haven't dug deeper into details on that.

2800kWp => 2800Wp :)

And 80% of your solar installation cost is labour...

We're paid £0.18 to generate (subsidised), £0.15 to export, and if I shift load via our battery, all our import is £0.07 per KWh.

Even with a large house, homelab, and an EV, we barely pay for electricity over the year. Doesn't seem like a con to me.

You've only done the maths for half of one side of the equation.

Remember that money is numbers in computers and joules and watts are real. Incentives and taxes are there so some things are easier to make real than others.

You've done none of either side of the equation.

Please present this magical equation to us, mere mortals.

If you were more explicit about your equation, we could actually discuss it. Trading quips doesn't further the conversation.

It’s a con in the same way a generator is a con. Yes of course utility scale PV is much cheaper, but this way you get control of your own supply and demand.

> The ROI of a large PV farm must be substantially better than a home scale install.

Actually, it's the other way around.

A rooftop solar doesn't require much: the land is already there (it's yours), there isn't any bullshit with permits, all you need is a ladder or a bucket truck, a few ultra cheap panels, an aluminum frame, an inverter and a few dozen feet worth of wiring.

A large scale solar farm however? The developer needs to find suitable land (challenging to do when competing against big ag), there's permit paperwork involved because solar farms ain't agriculture, they need to pay for a high voltage connection to the nearest substation, the huge ass panels need a really solid support construction that can withstand wind and weather and that needs a solid foundation as well, you need thousands of feet worth of wiring, complex and massive inverters, lightning arrestors, god knows what.

Oh and you get resilience against natural disasters for free on top of that. Some drunk driver plows into a power pole, some redneck shoots up some birds and kills the power line (yes, that happens so often that utilities release yearly reminders to please leave the birds alone), or a heavy storm / flood takes out entire substations for weeks, whatever - you throw the transfer switch, kill off all the non-essential consumers and can easily ride through a week worth of outage.

You might want to start playing factorio ;-)

The answer is yes: it is a lot easier to make a PV farm than a home scale install!

I don't get the joke. I mean, I understand factorio. But in factorio, "home scale" is extra easy. You can craft a handful of solar panels in your back pocket, no need to even think about setting up a production line.

On the long road to 1M SPM already :)

While I oppose climate hysteria, climate change is a consumer responsibility. You must limit your energy use, and you must choose better, more responsible options. Companies just do what consumers demand, they don't force anything onto anyone. There are lots of green energy power companies, I'd use one of them.

Human cognition has weird failure models that modern advertising can exploit. Free choices can only happen with a free mind, but unfortunately we have this weakness that makes us prone to manipulation. (this is also exploited by political propaganda)

We can still individually make better choices, and also eat our vegetables, etc, but in the aggregate public policy is more efficient to make the large scale changes we need

>Free choices can only happen with a free mind

And perfect information. Too bad 0% of consumers have the expertise and time to fully audit the supply chain of every product/service even assuming they could get ahold of that information.

> [companies] don't force anything onto anyone

They don't force at gunpoint. They use cash and lies to convince. And the legal system to cow.

https://en.wikipedia.org/wiki/ExxonMobil_climate_change_deni...

https://en.wikipedia.org/wiki/Steven_Donziger

You aren't wrong that we should choose better. But what do you do when so much money and effort has been expended to ensure so many people don't know what better even is.

I'm sorry if what I wrote made it sound like I don't take the climate crisis seriously. Quite the opposite which is why I think it's important we allocate resources to it efficiently.

Why go for a bigger battery when you can just put more panels on the roof to cover those winter days and waste the power the rest of the year?

I suspect the answer is somewhere in the middle - maybe two weeks of storage. Though of course prices change all the time so the correct action will change and you need to rerun the numbers as things degrade to decide your next action.

(Author here) My roof is full on both sides. There simply isn't any more room.

I do say:

> As solar panels increase in efficiency, it might be more sensible to replace the panels on my roof, or add some onto a shed.

Even in the darkest days of winter, they still generate something (unless they're physically covered in snow) - but they'd need to be 20x as efficient to power my typical winter usage.

Solar panels are already at least 20% efficient (most are better than that). I don't think they'll improve much beyond 30% within the next 20 years. Your 20x aspiration is of course technically impossible.

Did you DIY? Our installer basically only put panels on the sunniest sides of our home. I'm surprised you went with panels on all sides.

We didn't DIY. Our installer was happy to put the panels wherever we wanted.

Our roof is an even East/West split. So one side powers our morning and the other side our afternoon.

Depends on the part of the world, but in northern/central europe the production of panels from september/october to march is zero, 0, according to my colleague in his roof and many others have said the same. It is cloudy, it will rain a lot and during winter if there are no clouds then there are only.. a limited number of sunglight possible, and the sun is low, so most of the "power" is already absorbed by the atmosphere

I'm not sure how far up north you're talking about, but solar production in Stockholm (and I'd argue anywhere north affects so few people that we can completely ignore it for a general discussion) is about 10% of summer production but certainly not 0.

https://profilesolar.com/locations/Sweden/Stockholm/

Stockholm doesn't really have snow that covers the roofs to a degree that matters.

Also, the labor of keeping your roof snow-free is not really worth the savings.

In our part of the world, solar production during winter is incredibly low or 0 due to it being very cloudy, days being much shorter, sunlight angle on the panel very suboptimal. No amount of additional panels will get you through that streak.

It also depends somewhat on how much energy you use. I live in the Netherlands where everytime I bring it up, I'm told "that's just not possible, you will never make enough in winter", but these same people have no idea how much energy I use. On a bad day, I use maybe 10kWh and that's running the AC with the thermostat set to 19c overnight and a bit during the day at 22c. I don't have a giant fridge, I don't have any gaming PCs slurping 200W on standby, etc. My baseline usage is around 300-400W to run the old freezer that never turns off (70W), my network equipment, a fan in the garage to prevent moisture buildup, and some lights.

My 1.8kWh system at 20% output covers a great percentage of my baseline usage during the day! I'm probably going to add a small battery so I'm not penalized for sending energy back to the grid, but I'm not gonna need much until my kids get older and want new gadgets. The cool part about modern electronics is that we're generally getting more efficient too with newer tech. If I replace the old freezer, my baseline usage drops 20%+.

I don't disagree with your point that sometimes nature is simply just working too hard against your efforts, but I also wrote all this to say that some people need to really do the math and not rely on "common knowledge". Energy efficiency has come an extremely long way in the past decade and much of what was true when residential solar first started popping off is now outdated.

Electronics is not the issue of electricity usage in winter - heating is. Of course, if one uses fossil fuels for heating, it might seem one doesn't need that much electricity to survive winter.

> I'm not gonna need much until my kids get older and want new gadgets.

FWIW, a MacBook Pro in active use uses like 45 watts max and an iPhone really like 2-7 depending on the use. I wouldn't worry too much about gadgets.

I wouldn't say no amount. I think about 100kW of solar would still produce enough for the average house even in the depths of cloudy British winter.

Way too much to fit on a house though.

while that's true, getting close has major benefits. adding extra capacity for the winter also adds capacity for fall and spring. that production will reduce how many weeks the battery is needed for

Because batteries are cheap and only take minutes to install.

Closer to the polar circle than the equator. 17.6 kWp (44 panels), south-facing

2024:

May: 2494 kWh

Jun: 2323

Jul: 1915

Aug: 1634

Sep: 1008

Oct: 442

Nov: 185

Dec: 31

2025:

Jan: 43

Feb: 335

Mar: 980

Apr: 1510

In the category of doing obnoxious things for shock value, why stop at merely making sure you have enough batteries to keep you covered during the *average* year? Why not make sure that your home is going to be fully self sufficient in 99.99% of years? That probably adds another 50-150% to the total amount of storage that you would need.

But also, the expensive thing about batteries is typically the amount of power they can produce. The post used lithium ion batteries as a reference point, and those typically have a power rating between 1 and 4 hours - meaning they can fully discharge an entire summer's worth of stored energy in 4 hours... which is probably not something you need to pay for.

If you want a ton of really cheap long term energy storage, you'd look into a technology more like hydrogen fuel cells. The raw power (for standard home, 10 kW is plenty overkill) is going to be more expensive than lithium, but for storage you just need a bunch of hydrogen stored somewhere safe (probably buried underground in your yard). That's much, much cheaper than lithium ion batteries on a per kWh basis, especially if you are scaling up into the MWh territory.

And, the other big cost saving solution is to just add more panels. It means you'll be overproducing in the summer and you'll have to curtail, but some curtailment in the summer is a lot cheaper than finding a way to ferry all of that energy into the winter. Then you have extra panels in the winter and you don't need as much storage to be fully self sufficient.

it would also be really cool to use excess power generation to drive atmospheric petroleum synthesis (pull carbon from air to make hydrocarbons); then sell it or store it for later use.

I know the tech is not quite there yet, but it’s getting closer every year.

Storing hydrogen at home is not going to be cheap though, is it? At that point it would be worth to look at storing eg methanol.

Use heat and pressure and electricity and you can convert CO2 and Hydrogen into Methane.

Methane when burned releases the CO2 back into the atmosphere, but if you're mining the CO2 from the atmosphere to begin with it pretty close to carbon neutral fuel.

https://news.osu.edu/turning-carbon-emissions-into-methane-f...

Hydrogen would be a terrible approach due to the low round-trip efficiency and the need to store huge amounts of compressed/cryogenic gas, but iron air batteries seem like they could actually do this.

Most people have the wrong idea about hydrogen fuel cells because the media almost exclusively talks about them in the context of cars.

When your fuel cell can be stationary and heavy and large, you can hit efficiencies above 50% without cogeneration and above 80% with cogeneration.

Does that number include electrolysis? I didn’t realize that kind of round trip efficiency was possible.

Yes it does!

Yes I love having bombs buried in my back yard. Very exciting.

Why are you afraid of hydrogen? Compared to the lithium ion batteries or even the LPG or petrol for a generator hydrogen is very safe. It's a common misconception that hydrogen is dangerous. You can stick a flame into pure hydrogen and nothing will happen. It's only if you mix with oxygen that it becomes dangerous, but because hydrogen is lighter than air it's going to dissipate very quickly if you have a leak in your container (unlike e.g. Gasoline fumes)

I'm afraid of hydrogen due to hydrogen embrittlement. I wouldn't appreciate my high pressure tanks turning into bombs (no ignition or O2 required).

The Humanity.

Something that isn't spoken about enough is that in developed Western countries, grids are actually significantly oversized due to reductions in electricity usage over time [1]. That link says 16% over, but the peak demand in the UK in 2024 was actually only 45MW [2], which I make more like a 30% reduction from the all-time peak.

Because of this, it feels like we should already have enough transmission capacity in a decent part of the network to cope with a re-organisation of where the sources and sinks are placed. Yes, we might need to do some work in the last mile, especially if V2G takes off, but things aren't nearly as bad as one might naively assume.

[1] https://www.nationalgrid.com/stories/journey-to-net-zero-sto...

[2] https://www.neso.energy/news/britains-electricity-explained-...

It depends. In a neighboring county they have effectively saturated the grid and had to put a hold on datacenter permits. AI has been undoing a bunch of the efficiency savings we worked hard for in the past 20-30 years.

The trouble is the capacity is in the wrong place; the UK closed coal plants in (defunct) coalfields in the middle of the country, and built offshore wind farms which tend to be further north. There's plans for an offshore north-south connector to help with this.

True, but don't forget you can put BESS on the sites of the old coal plants: https://www.bbc.co.uk/future/article/20240927-how-coal-fired...

That connector goes underwater right where I grew up. I haven't visited mother for a few months but afaik they haven't begun digging yet.

In some parts of my country the grid provider has needed to restrict new industrial connections because the grid is hitting its limits.

https://yle-fi.translate.goog/a/74-20138415?_x_tr_sl=auto&_x...

OK, but Finland has the lowest electricity prices in Europe and is pretty cold for most of the year. It makes sense that people want to put datacenters there.

Electricity needs are expected to rise significantly as we convert heating and transportation to electric.

Not as much as you might think: one of the links I gave suggests only an overall 10% increase if the entire country switches to EVs. I found another link suggesting a 25% average increase if we all switch to heat pumps -- still within what the grid is sized for already.

Heat Pumps will be the big driver but there’s a lot of spare electricity capacity over night in most European countries

> in developed Western countries, grids are actually significantly oversized

Your sources really only apply to Britain and other deïndustrialising countries. American and European energy demand is rising due to electrification and AI.

For Europe at least, measured numbers are flat or slightly falling: https://www.iea.org/regions/europe/electricity

I accept that AI is likely to take us in the wrong direction for a while. (I don't think it will actually be that long, once people realise that more training isn't getting more results.)

In the US, iirc replacing combustion cars and heating with EVs and heat pumps are larger contributors - the inflation reduction act and various incentives have been pretty successful, and as a consequence, electricity demand has been growing much quicker recently than in the previous couple decades.

How much of Europe is still electrifying? Or I suppose you mean migrating fossil fuel heating loads to electric?

> migrating fossil fuel heating loads to electric?

Yes.

> peak demand in the UK in 2024 was actually only 45MW

It was actually 1000 times that much.

Correct, thankyou: stupid error on my part. 45GW.

A small addendum on the conclusions:

- every household, can do that, _if_ they have a roof. appartment buildings may not have enough roof for all the people in it.

- for those who can't access that, (that includes people, but also the industry, your mobile phone provider, etc.) prices will get worse.

- the fire brigade will love industrial-size battery fires in the neighbourhood.

Germans seem to be rather fond of balcony solar

https://en.wikipedia.org/wiki/Balcony_solar_power

Balcony solar is absolute awesome in germany. I get about 30% return on investment per year on my small solar panel. Hard not to do it. I have no idea why it is still a little niche

For some reason in the USA there is only a single state that has approved that (Utah).

It conflicts with some of the NEC (national electric code) requirements. That all needs to get sorted out.

The NEC is also in conflict with homeowners performing simple electrical work, such as replacing switches and outlets.

It is. But in this case the conflict is more fundamental - the NEC has no provision for a circuit that has multiple electrical supplies.

If you have a circuit rated for 15 amps, and plug in 12 amps of solar, then the breaker won't trip until the circuit load exceeds 27 amps, which seems bad.

Hmm, if you have an appliance (like a clothes dryer) with a dedicated circuit, it seems like you could solve this by connecting there. If you have the balcony solar device plug into the wall and the appliance plug into the balcony solar device, then you can easily put an additional circuit breaker where it's needed.

Not all homeowners are built for even these simple tasks. I watched someone try to replace a receptacle live, all while wondering why it was arcing and tripping the breaker repeatedly.

My solution would be using trade schools to run a homeowner electrician's program, teaching folks basic safety, measurement, and mechanics of what they would need do the work safely.

A program like this shouldn't take more than a weekend to cover all the issues including a Hands-On lab. A second weekend could be added for ground mounted solar setups.

I'd be willing to pay a couple hundred bucks get such a ticket.

Uhhh...how long exactly did you "watch" this?

Did something change? Iirc you can do that sort of job yourself.

That's just low hanging fruit, the easiest and cheapest way to produce some solar power. But even if fully utilized, that is not going to come anywhere close to meeting most households' needs.

That's an interesting way to word "the most efficient way". A solar setup that meets the energy needs of the entire household is going to have to be oversized, which is a waste. Meanwhile, 100% of the output of balcony solar is almost always going to be fully utilized by the household, meaning 100% of your investment goes into lowering your ever-rising electricity bill.

Any time you're exporting to the grid, you're losing out - the rates are never good. Check out the OP's graph. His setup is oversized by about 2x. He's exporting to the grid for most of the day, which is hardly useful, then pulling from the grid after 6pm - the worst of both worlds. Downsizing the solar setup 2x and investing that into batteries would be much better.

> your ever-rising electricity bill.

It's not a surprise that your bill is rising if people consume less during the day because they install balcony solar, but don't meaningfully change their peak consumption, and therefore, don't meaningfully reduce the grid investment required.

At least the blog's author has a battery setup which meaningfully moves their peak draw.

No, but I'm on a TOU plan where electricity costs me more from 4-8pm, and I get direct afternoon sun. If balcony solar could halve the electricity usage of my AC from like 2-6 in the summer, that would be pretty nice.

You forgot to mention anybody who has a yard that gets full sun can mount panels there as well. As far as fires you can say same thing about all the fires that currently occur because of propane, gas, and heating oil. Those have become some engrained in society for so long that you don't even think of that as a "fire hazard therefore you shouldn't even have it".

The fire thing is funny with cars. If an EV burns, it’s important news. An ICE car burning is unremarkable.

> You forgot to mention anybody who has a yard that gets full sun can mount panels there as well.

The overlap with people who have their own solar-compatible roof is probably large.

Solar and renewables in general are starting to reduce generation costs.

So once the improvements in power transmission are done prices should come down for everyone.

Solar and renewables alone don't make a grid. You would also need grid-scale batteries, and the cost is not the same.

The "improvements" in power transmission is about building more lines, these lines are not going to be significantly cheaper to maintain than previous generations, and if these investment/maintenance costs are shared among less, that means more expensive electricity. Currently, in my country, electricity transport and distribution are about one third of total cost.

You have to consider that electricity will be 3x over the next 50 years (for transportation and heating). So we are currently building out a lot of extra infrastructure.

Grid scale batteries will also primarily reduce cost by offering arbitration.

For the right kind of storage, even high loss storage could be worth it, if it is long-duration storage.

The problem is economics with for-profit generation, not storage cost: If the cost of generation from PV was equitable, you would "store" your volts in the supply chain and withdraw from the bank over winter. Then the storage (at loss to transport) would be in Dams and other long duration spaces.

In most cases every residential system is getting payment rates at least that good.

The problem is that wH-for-wH doesn't take into account distribution costs, which is most of the residential cost of electricity, and that a wH at noon in July doesn't cost the same to generate as a wH at 2am in February.

For most jurisdictions you can look up the large industrial rates to find the wholesale energy rates. Residential solar is worth about half of that 'reliable' electricity rate.

This type of thing would really need to be implemented at the township / local community level at least, similarly to how every house doesn’t have a big electrical substation plugged into the high-voltage power mains with explosive oil-cooled transformers. It’s simply not realistic to think every private dwelling can or should have this kind of capability, to say nothing of the cost. Maybe large communal housing could. Ultimately it’s a sort of social optimization problem and I don’t think giant individual capacity solves it efficiently.

One thing that could possibly work better IMO is something like a small local renewable fuel economy where excess power is used to produce hydrocarbon fuel by catalysis of electrolyzed hydrogen with carbon sources, and individuals can purchase this fuel to recover the energy, or possibly the power plant could use it during solar lows.

The advantage of this type of system is that it’s not really capacity limited, as long as you have enough fuel storage, which is simple to build more of.

of course, you could just use alcohols distilled from fermented plants instead, but that’s not as sexy.

>This type of thing would really need to be implemented at the township / local community level at least,

Even better - both. Increase the independence and redundancy in several steps, making the grid more reliable and less prone to failure from single events.

>It’s simply not realistic to think every private dwelling can or should have this kind of capability,

Why not? You can get 10 kwh of storage for the price of a phone and laptop. Any EV has more battery than what's needed to power a home for days, some of them already have the capability to do so when combined with the right charging station.

Of course not everyone will have it, but surely battery storage could become as common as air conditioning or central heating even at current prices.

Why liquid fuels or chemistry at all? Something simple like moving blocks of cement uphill with a motor/generator would be more efficient.

Run the numbers and you'll find that blocks of cement are pretty expensive compared to the batteries!

Over the past decade there's been several startups trying to do gravitmetric non-hydro grid storage, and even with favorable conditions (e.g. a large free train track on the side of a mountain) they can't get the economics to work. Plus, that tech is never getting cheaper, like batteries are every day.

Do the math on energy density. 1 kg of fuel contains roughly 45 MJ, which would require you to lift 1 kg of cement 4.000 km up.

Or, alternatively, 1 liter of petrol has enough energy to lift a 3 tonne cement block 1 kilometer upwards.

I think this is something that may happen in the next decade.

The interesting impact will be on the grid itself. Why connect to the grid if you are self-sufficient?

Then the grid starts to degrade due to lack of maintenance, and the people that can't afford local storage become dependent essentially on a government maintained service.

Or should we be planning localized storage and grids at the same time, so we get the benefits of both scale and resiliency and redundancy.

People will be parking a mobile 100kWh battery at their house every night. We need integrated V2G and grid upgrades to make the most of this opportunity.

> Then the grid starts to degrade due to lack of maintenance, and the people that can't afford local storage become dependent essentially on a government maintained service.

Many services that we use in our daily lives are government maintained services, so electricity is no different than water, sewage, internet, roads, railroads, post, emergency services, public education, public health systems, trash and recycling services, parks and recreational spaces, disaster relief and response, and others.

We should absolutely ensure these services continue to be funded and maintained, because they're often not profitable to deliver. Especially to the sprawling population of the United States. That’s exactly why government support exists and should exist: to guarantee access to essential services that markets alone won’t reliably or equitably provide.

I do not think this will happen. Getting most households to be self-sufficient is probably not as cost effective as centralized grid. One there's the economy of scale. Second, any peaks and troughs will generally be balanced out between households and the overall buffer (aka reserve) needed could be lower.

If local storage becomes cheaper than the grid but some people can’t afford it (why, capital costs?) then the government would be better off addressing those capital costs directly.

However, you need to consider industrial and commercial use as well as domestic. Can you power a smelter using local solar?

Probably? https://reneweconomy.com.au/solar-battery-deal-for-giant-sme...

I'm fully off grid today with no issues, even had power company remove power poles. I do heat with wood however. AC in the summer is no issue since that is when I get the most sun anyways.

Imagining you combining these by burning the power poles..

> Why connect to the grid if you are self-sufficient?

I think that starts to bleed into the "pre paid meter" vs contract argument.

but practically the difference between total self sufficiency and 90% is willingness to fork out cash.

I currently have a 13kwhr battery, which covers my domestic power needs for 75% of the year. (we'll start to draw on the grid in the next few weeks.) but in the dead of winter it'll only cover 20-50% of my daily need (excluding the car)

but for car power, thats a different beast. Even though I don't commute by car, with the charging at home, I now use around the same amount of power as the uk average house. (even with solar and storage. pre electic car era. )

There's a certain type of person who fantasizes about being off-grid, but the few that actually live it know the hassle and generally want to get back on if feasible.

Battery costs might go down, but the space they take up on your property costs money as well, which only gets more expensive the more urban you are.

The island of Eigg has a micro-grid. Not individual houses, a micro-grid.

The UK is going to be a wind power island not a solar power island, and definitely not an individual solar power island.

This doom-loop is often repeated, but reality is far more complicated.

Very few people go fully off-grid, reality is people don't want that. Cost/benefit just isn't there unless you live off in the woods.

So instead, market structures react when penetration % becomes non-neglible. First you start seeing things like fixed-fees (minimum prices to maintain a grid connection, or "first x kWh are included"). And then you start seeing like what's in California with NEM3: the grid-export prices drop to "we don't want your excess solar" so people are incentivized to buy batteries. But because batteries make a system more complicated and expensive, people buy smaller systems overall.

So the "too much solar creates a disconnection spiral and the system falls apart" thing is a bit of fear-mongering. The system adapts, the changes in pricing create different cost/benefit ratios, and if nothing else, new AI datacenters will gobble up any power that doesn't need to flow to neighborhoods.

It's not the way that it was originally meant, but this is another interpretation of the phrase "energy too cheap to meter".

> In the last decade lithium ion battery prices have fallen 90%

The price of batteries has declined by 97% in the last three decades: https://ourworldindata.org/battery-price-decline

The winter months and parts of the fall months are hardest due to a lack of sunshine. Without an EV, from March until late September a 5kWh battery is enough for me to keep my daily grid power consumption close to 0. A 5kWh plug-in battery now costs around 1299EUR. Pays back itself in a handful of years.

Batteries are similar to solar panels in this regard. With solar, the first couple of kilowatt-peak delivers the biggest savings. With batteries, it's the same with the first couple of kWh of storage capacity.

What battery you have in mind? Can you share name/model?

Marstek Venus E (5.12kWh), this plug-in model has gained a lot of popularity the last couple of months in some European markets like Belgium, Germany, and the Netherlands. It has a maximum charge rate of 2500W and can discharge at up to 2500W (should be connected to a separate power group and only if local regulations allow it). These kind of batteries plug into a regular AC socket and do not require an electrical inspection. But they aren't legal everywhere.

In my case, it's configured to track the readings of my digital electricity meter. The battery charges itself when my solar panels produce excess power and discharges when it detects grid consumption. Throughout the day, it buffers the intermittent solar power, and during the evening, night, and early morning hours, it keeps my grid power consumption close to zero.

Why worry about panels and batteries when you can have an Egg?

https://enron.com/pages/the-egg?srsltid=AfmBOoqW03cqyIhQ0OlG...

And the price of the egg?

The egg itself is extremely cheap. The only expensive part is the subscription to disable remote control rights from Enron's traders.

If you consider the fact that only half of Earth is experiencing summer while the other half is experiencing winter, there's an obvious madlad solution to instead of storing power, transfer it from the summer hemisphere solar panels to the winter hemisphere electric heaters, somehow.

If you also consider half the Earth is experiencing day, while the other half is experiencing night, there's another benefit to transferring the power East/West as well as North/Sourth. Perhaps by doing both, we could create some kind of "power grid"...

That's just me being snarky, but we've been scaling towards this for decades, we just haven't fully gotten there. We can probably solve the technical problems, it seems the main issue to building a fully-connected worldwide power grid is that the cost of scaling that much isn't worth it (yet).

It would be extremely expensive and also risky.

One of the problems with our reliance on oil is that so much comes from an unstable part of the world (although the oil itself contributes to the instability).

Cables under the ocean can be cut by anyone who can get to them with a submarine.

You would be look at cable literally going around the world - at least a good proportion of half way round to be useful. They will be vulnerable one way or another at some point.

Then there is reliability. There have been some fairly bad failures of national power grids. A failure in a global grid would be a lot worse.

Might be easier to use satellites to send the sun to the other hemisphere

https://www.reflectorbital.com/

Good thing that could never be used as a "death ray".

They currently most efficent method is called HVDC and it's not really efficient enough to be anyhing resembling economic at those distances. Ohm's law is a thing.

Edit: I again made the mistake to comment on a thread dealing with energy x politics. Sorry, I'll try not to do that again. I'm out. It's feral.

HVDC is actually incredibly efficient over long distances. The conversion losses typically dominate.

The trick is the "HV" part. China is already running 1100kv on some of their HVDC lines. Transmission losses decrease with the square of voltage, so any increment from that point would be very substantial.

> They currently most efficent method is called HVDC and it's not really efficient enough to be anyhing resembling economic at those distances. Ohm's law is a thing. > > Edit: I again made the mistake to comment on a thread dealing with energy x politics. Sorry, I'll try not to do that again. I'm out. It's feral.

I didn't see any feral responses? Did you not like the ones that pointed out that losses over 800km are <3%, and so your assertion that Ohmic losses are the issue is essentially wrong?

The only feral-like response here is the OP's follow-up "Bullshit..." itself.

UHVDC is 2.6% loss per 800km so after 8000km you have 76.8% left. That's not too bad. Although I obviously don't know what distances you had in mind.

Bullshit.

What voltage is UHVDC at those numbers? Who is supplying the equipment? Where are the demo installations? What's the cost?

Again, the goal is economic very long distance transfer of electric power. Not a Chinese university research project.

I don't get why you're feeling so attacked? I'm just citing the numbers. UHVDC is defined as >=800kV

> "HVDC transmission has typically 30-50% less transmission loss than comparable alternating current overhead lines. (For comparison: given 2500 MW transmitted power on 800 km of overhead line, the loss with a conventional 400-kv AC line is 9.4%; with HVDC transmission at 500 kV, it is only 6%, and at 800 kV it is just 2.6%.)" [1]

There are quite a few of UHVDC lines in China, not much in the rest of the world. [0] I don't know what they cost, but maybe you can estimate it based on what they decided to invest over a 10y period.

[0] https://en.wikipedia.org/wiki/Ultra-high-voltage_electricity...

[1] https://web.archive.org/web/20180730045905/https://www.sieme...

[flagged]

What is "not efficient enough"?

As a first guess, one would think it makes more sense to eat 30% loss (so you need 1/0.7=143% installed capacity) than to need 200% capacity plus batteries since it's night about half the time on average. And afaik HVDC is more on the order of ~15% loss

Aside from the physics, HVDC doesn't compete successfully on cost. It's cheaper to overbuild PV and use batteries.

... aside from the physics? What factors into this cost calculation other than the physics of solar panels, batteries, and cables?

Infrastructure (heck, just the conversion points alone are a huge part of the cost), but also regulatory hurdles like getting rights-of-way. Running an HVDC line is quite expensive; last time I saw the numbers crunched, it was basically impossible to make it work financially, no matter how efficient the lines were.

I'm considering buying enough batteries for my day usage, then recharging off the grid during off-peak hours. I can add solar later on.

The panels are the cheapest components. If you're incurring all the costs to retrofit your electrical panel with an inverter + batteries, you may as well implement on-site generation from the start to recoup more of the costs.

An odd thing about this article is that it ignores the deeper question: what balance of solar over-provisonioning + battery would most cost-effectively cover anticipated yearly needs?

I suspect that something like 3x'ing the solar (under 100k) would then let the author get away with much, much less battery, and result in a net cost savings.

Yeah seems like a relatively simple maths/econ problem to solve for, given some parameters like local solar power per m2 in the various seasons, electricity use in the various seasons and time of the day, and LCOE of solar and battery storage.

My guess is the differences in either choice aren't huge, as both solar and battery storage keeps getting cheaper.

Having an electric vehicle can really help, also. It basically soaks up excess solar power of an outsized installation during much of the year (making the payback time on the outsized installation very good), and can be charged away from the house during a few low-chance bad winter days when the outsized installation is enough to power the house but not the car. Electric cars are charged fully about 3 times per month on average in the US, so working around that with smart charging is not a complex challenge in the next decade.

I think he can't imagine 3x'ing because he already has his house covered and only the shed roof remains empty.

But that is a super interesting question that immediately comes to mind.

I am pretty sceptical about batteries and see overbuilding renewables plus bitcoin mining to monetize excess as a more viable solution.

The HTW Berlin has a autarchy calculator. Unfortunately only in German language: https://solar.htw-berlin.de/rechner/unabhaengigkeitsrechner/

They also test and publish yearly the latest battery combos.

Extremely underrated how important just a small battery is for autarchy, very useful site.

The calculator makes it very clear that adding more batteries becomes more and more inefficient.

Being 100% independent is just completely unnecessary.

In case you didn't realize he is looking to store ALL of the summer generation into a battery and generate zero power in winter.. so rely entirely off of a battery during winter.. which is absolutely no feasible for a normal person and nobody would ever do.

I once did a related calculation on "How much of my garden do I need to dedicate to coppiced willow to heat my house for a week per year?"

I concluded that we're all going to need much bigger gardens.

> It is possible that, not too long in the future, every home could also have a 1 MegaWatt-hour battery. They would be able to capture all the excess solar power generated in a year.

Seems like we'll get to a point where adding extra panels "makes economic sense" long before this kind of storage makes sense.

I wonder if compressed air energy storage systems can be built for homes. It can be a tank part of the foundation. Too small CAES doesn't work, too large may get messy, but a house size tank might be best.

Crashing panel prices, output degradation, local and state laws, and most importantly, bidirectional charging should all play into the long term calculations.

I always thought about this myself in terms of personal sized long term, high density energy storage. Compressed hydrogen with a fuel cell is the obvious solution. Excess electric is used in a electrolysis cell and a matched compressor fills a bank of storage cylinders. More cylinders = more storage. Though likely very inefficient with a risk of fire or explosion.

Are there any other long term high density electric storage technologies that can fit in someones basement, garage, or even apartment closet?

> Compressed hydrogen with a fuel cell is the obvious solution.

To achieve volumetric energy density of hydrogen at room temperature that's on par with batteries (and that's charitably assuming you're using inefficient resistance heating with batteries) you need to store it at a pressure in the order of 100 bar.

You're better off with batteries realistically speaking.

Compressed hydrogen is no joke. It can escape most containers, actively degrades many grades of steel, has a very low ignition energy, and will explode over an enormous range of air/fuel ratios. Definitely not something to keep anywhere where you care about the roof :)

https://archive.is/wOP3A (the site seems to be struggling under the load, e.g. not showing images)

Batteries self discharge. There is no system that will hold 100% charge for several days.

It wouldn't need to. It would start discharging at sunset and only stop at sunrise. And in winter it would spend most of its time discharging.

But, as I say in the post, this is a bit of fun looking at extremes.

I’ve been puzzled by a number of houses near me with panels on the north-facing roof. Are panels really that cheap that it makes sense or are people that stupid?

Let me guess why this is coming on, its top-up time on our solar energy bills. Those transport fees on externally sourced electricity sucks.

Nobody would even blink if a rural home had a 500 gallon horizontal propane tank, and that represents 20x the energy content of a 1MWh battery pack.

Relevant video from USCSB, from a propane explosion in 2007 that killed four people.

https://youtu.be/JzdnUZReoLM?feature=shared

It would make me nervous, although that's only due to my engineering background.

In any case, it all depends on what you want to stand next to. A large explosion, or a multi-day metal fire releasing clouds of hydrogen flouride.

If the metal fire is over multiple days, you can walk away from it. The large explosion can kill you before you know there's a problem.

> What I want to do is find out what the maximum size battery I would need in order to store all of summer's electricity for use in winter.

This is ridiculous. It's like asking how much propane do I need to store in summer to go the whole winter? You would need a tank so big it could fill up propane tankers. Thus why we get regular deliveries of propane throughout the year on an as-needed basis... and why you should only have enough battery to store the peak energy use for a couple days at most. If you have an extended period of no sun, first you reduce your energy use, and then you top up with a generator. This is far cheaper and more flexible than having a gigantic battery array for an edge case.

22kWh in battery (self-contained units, BMS, heating element, etc) costs <$4400 in the US, shipped from China, for a reputable (but not pricey-brand) battery provider. More than enough to power most homes (in Northeast US, cold winters without much sun) for a couple days. Add in everything else you need (wiring, solar panels, power inverter(s), MPPT(s), generator, etc) and you get to $6.5k-$9k

If you want 100% GHG reduction, for every 1 watt nameplate solar rating, 1 x 0.2 capacity factor x 730 hours a month x 3 months a season = 438 Watt-hour of battery or other energy storage. 80% reduction needs 100 hour vs a whole season, so 20 watt-hour required storage. Dr. Chu of Stanford is my source.

Another way to look at this: how much solar do you need to synthesize 1 MWh of methanol ("e-methanol") from water, which is only ~54 gallons (200 liters)? Actually you need 135 gallons since the generator is likely 40% efficient (or less..). This is not much fuel, I used to have two 275 gallon oil tanks in my basement.

I think e-methanol synthesis is ~%50% efficient, so double the solar. Doesn't sound so bad.

Now if you could synthesize methane you could push it into the gas grid and run the meters backwards, thereby avoiding the need for storage... actually methane synthesis is even more efficient, >70%.

At which point does this become a huge fire hazard?

A friend has his own battery setup in a shed. He has a ton of sand above it which would collapse in the event of a fire.

I have 1000 litres of heating oil in my back garden which is hardly unflamable. 10MWh of fuel.

Can LION battery fires be smothered? Online articles are contradictory. Some say they can be smothered, but others say that they generate their own oxygen, and you need to cool the fire, some say to do both.

Heating oil in a tank is quite safe. It doesn't evaporate rapidly, and will not burn unless atomized or spread out. It won't explode unless provided with a much richer source of oxygen than normal atmospheric pressure air.

The cars in people's garages are far bigger fire risks. For example it's not uncommon to have a 70kWh+ EV battery, and the chemistries used to get the extra energy density for cars are far more unstable.

LFP (rarely used for cars) is fairly stable. And sodium batteries are even more stable.

Pretty quickly. There's also a point where it becomes a serious explosion risk too.

Every other fire you can stop if you're right there and you catch it. If a battery pack starts to go, you might have a few seconds before the local environment is incompatible with life.

Not all battery technology is as volatile as Lithium-Ion or Lithium Polymer, LiFePO4 for example isn't subject to thermal runaway, nor are some of the Sodium-Ion batteries (although it's dependent on the exact chemistry being used).

People are used to having 25MWh of heating oil tanks in rural locations, although those are supposed to be stored away from the house.

Assuming heating oil is diesel, it's not very flammable and not a huge fire hazard. Soil pollution from leaks and spills seems like a bigger concern there. But I guess some people have large tanks of LPG which might be a bigger danger?

Nobody seems to think twice about storing gasoline, heating oil, diesel, and/or propane around their place.

None of those release hydrogen flouride when they burn (among other things).

LFP cells are used in these batteries, they are not the same chemistry as the li-po you find in smartphones.

I'm in the middle of a renovation now, that will include batteries and solar.

One thing that I never see mentioned is how to support on-demand instant hot water heaters.

The 6.5 gal/min heater (what it takes to fill a tub) that I'm installing uses 100A at 220v when operating!

I haven't found any battery system that can support that.

Do "totally off-grid houses" all use a typical electric storage tank hot water heater? For my solo occupation, that's a lot of hot water storage over times when almost none is being used.

I do have a smaller water heater under the kitchen sink, so that the giant one doesn't have to run for that usage.

How do off-grid homes deal with the high instantaneous current consumption of on-demand water heaters?

They don't. You either have a solarthermal system to heat the water, or you use a tank to store hot water. I've previously installed an "iBoost" which diverted excess solar into an immersion heater.

Heating slow(er) and storing is going to be easier than suddenly ramping up for a shower.

I know batteries to generally be safe but am wondering if any folks are putting the battery systems outside of their home, let's say in a shed, detached garage, or a purpose built enclosure for batteries?

We have ours in a porch - mostly because the fan is slightly noisy.

I think the main consideration for any outbuilding would be whether it was water-tight, had some level of climate control, and was secure against theft.

Thanks, I think I saw some reference somewhere to consider the lithium in the batteries and safely keeping them in any space.

This would remain relative to climate and security needs though as you're pointing out.

In a cold climate you have to add heating and an insulated enclosure to keep them alive.

Bury them below the frost line in a concrete box with a sealed access port, add in some water cooling for when the battery heat goes above a cutoff. They'd never get too cold that way, stay around 60 Fahrenheit by default.

It's a nice back of the envelope calculation. I think the conclusions are correct for the stretch goal but it does not make economical sense. Yet (those sodium ion batteries could change that).

There are several things you might want to consider:

- wind, there are smallish turbines that you can put on your roof that generate a few kwh. Also when the sun doesn't shine. Extended periods without any wind at all are rare. 2-3 weeks would be a lot. That probably drops the amount of battery you actually need quite a lot.

- Second hand EVs are relatively cheap and come with some affordable batteries that are probably larger and cheaper per kwh than most commercial domestic storage solutions. Not for everyone but if you can wire things together, that might not be a bad option. Especially if you can get ,a good deal on some well used EV with a half decent battery. Relatively low loads might increase the life that battery has if you just use the car for storage.

- You don't have to generate the power next to the battery. Some cars can provide power to your house; when your house battery runs out, you can just use public chargers and drive back and forth to top up your house batteries. A bit of a chore but probably better than investing in batteries you don't need most of the year. Not a bad option if you live off grid. Batteries on wheels in general are a thing. Electrical semi trucks come with > 500-600kwh typically. That's a lot of power that you can move between your home and your charger. Container sized batteries are a thing. If you want to, you can get about 3-4mwh on your property. It's not going to be cheap. But it's doable. The point here is not that you can have a huge amount but that you could stretch a modest amount quite far by simply driving to and from the charger. Of course if you have a grid connection, using that is more convenient and cheaper.

- The capacity factor of your batteries is going to be a function of how often you cycle them. If you rarely cycle them fully, they are going to be relatively expensive. So, while hoarding batteries might make you feel nice and comfortable, it's not a great economical choice to make until batteries become a lot cheaper.

- The money you save on not paying for grid power needs to be balanced with the cost of a battery and how long it will last you (10-20 years?). If your monthly bill is 100, you might spend 1200$ per year and 12000$ for 10 years. So, that's your budget for a huge battery. If you factor in that it will have a low capacity factor, it might last quite long. Twenty or even more years. I have a lithium ion battery screwdriver that's nearly 20 years old; still fine. Because I rarely use it. So your budget could be 20-30K$ Adjust as needed based on grid prices and usage.

- As others mention, generators are relatively cheap and they do work if you can stand the noise and exhaust fumes. Not clean. But relatively cheap.

It's a valid thought experiment to repeat until the cost adds up. Your opportunity cost while you don't invest in this stuff is basically what you will continue to spend on the grid. Which is probably not horrible for most people. Until those cost curves cross, you are better off waiting. Or compromising and buying a battery that won't solve the whole problem but is cheap enough that it will earn itself back in a reasonable time.

It's trade off between need and cost. If you absolutely need to be off grid, it's doable if you have the space and resources. But it's not going to be cheap. Until then, some hybrid solution is probably more optimal.

I'm sure it would be much more cost-effective to have community storage, rather than individual storage, and it would balance the load a lot if some users used more power during th day than at night.

I think it's called a 'grid'.

In a manner of speaking, the grid is already the storage mechanism. In summer you sell the excess to the grid; in winter you buy it back. Obviously you pay more to buy than you get for selling but that's the premium for using someone else's infrastructure. You'd spend a load more buying a battery the size of a small house.

Snark aside, there are examples of community-scale energy infrastructure below grid-scale: see "district heating" and "co-gen plants". Sand battery people have been experimenting with neighborhood-scale infrastructure (though industrial heat uses is a better return on that tech right now)

I've also seen flywheels used locally.

It just makes much more sense to have a big battery where the local substation is, than for everyone to install megawatts of battery individually.

Of course then you have the collective action problem, and convincing your neighbors that grid storage is actually a real thing that exists. And that grid storage is not of the wrong political partisanship. The box of what's considered "politically incorrect" is getting fairly large these days:

https://www.theguardian.com/environment/2025/sep/10/south-da...

A car battery should be enough.

EV battery capacity is expected to grow to 100kWh.

People will park them at home every night, and probably somewhere with a charging point during the day.

Smart house energy management should be able to pick up on that usage pattern and use the car battery for the house while making sure the car is kept ready for use.

In the same way that wifi/mobile/satellite comms can keep us "always connected", the changes in power generation and storage are going to keep us "fully charged".

A house might use 20 to 30 kWh each day. Modern EVs have enough battery capacity to power some appliances for many days.

Vehicle-to-load ("V2L") is currently offered in vehicles made by Hyundai, Ford, GM, Volkswagen, Volvo, Mitsubishi and Nissan (the new LEAF).

Vehicle-to-grid (V2G) is more ambitious.

https://en.wikipedia.org/wiki/Vehicle-to-grid

The cost here is premature degradation of the battery due to additional charge/discharge cycles.

Not for the thought experiment of "I want my summer excess to power my winter usage" posed by the author.

In the UK you'd need a class D "loi-sonce" to be able to pull the shipping container sized battery trailer for that to work.

However, if you were wanting to use pure lead acid batteries for your house, because you'd be doing slow charge/discharge you'd probably be able to get away with just 1100 130ah lead acid car batteries.

I mean you'd be optimising for peak current, which isn't what you'd want. However it could be interesting to see what happens when you have ~500mega Amps at 48v. (24Mw would heat your radiators up pretty quick. )

for lithium, then you'd need 12-14 secondhand tesla/polstar batteries, which if they caught fire, might be a challenge to contain.

1100 car batteries might cost maybe $100-$200k and need replacing every 4 years.

Lead-acid car batteries are designed for high short-term current supply, for starting engines, not longevity. You can buy deep-cycle lead-acid batteries that last much longer, on the order of over ten years. Moreover, lead-acid batteries wear out when you discharge them too much more than by time elapsed, so taking good care of them can make them last even longer. Lead-acid batteries are great for standby storage, where you normally only discharge them a small amount between charging, but then need to use the whole capacity every now and again (for instance if you have a few dull days).

LiFePO3 batteries don't take as much wear from cycling, so they usually wear out from time elapsed instead of over-use. It's economically sensible to cycle LiFePO3 batteries as frequently as possible to get as much "benefit" out of the investment. They're great for time-shifting energy production by charging them at a cheap time of day and discharging them when you need the energy at an expensive time of day.

Did you take into account that lead acid batteries are recommended to only be discharged to 50% especially when used for solar ? If not thats now 2200 batteries and $200-$400K.

I eyeballed the maths on that. 1100 * 12v*130ah should give you a .7mwh of leeway to not do "deep" discharge.

"loi-sonce", would be better "loi-sunse". That 'o' is very jarring.

I was going for beeeergminghum, but for cockney, the o is indeed jarring

Not even close. A typical electric split will take 12a to maintain and that is just the heating/cooling system. Car batteries are meant for starts, not maintenance flow.

going forward, solar pv and batteries will continue to get cheaper, but each house will vary quite considerably in how to maximise and optimise things for what will always be an exercise in averages that is modified by whatever contingencies are included, and after living off grid for decades I could care less and recomend careing less about the math, start now with something modest, iterate,learn, end then install the largest system that you can. If you are going to build new, start with site selection, plan for car charging, and use all of the best practices for integrating passive solar into the homes structure.ie : homes built with double walls and a thermal break require NO home heat source as normal domestc activities will generate excess heat that must be vented. Anywhere north or south of 30° design should be for bad weather in the winter, and the rest of the year will almost certainly be gravy. For all refits and renovations to solar, the math will always be ,the most that will physicaly fit. Regulatory limitations will most certainly restrict batteries to a day or two backup in most situations.In most jurisdictions, a large battery would require a seperate building with significant set backs to any structure, untill we get to solid state non flamable batteries, which may be on the horison now.

You might want to factor latitude into your calculations.

https://www.recurrentauto.com/research/winter-ev-range-loss

> Remember, this is just a bit of fun. There's no practical way to build domestic batteries with this capacity using the technology of 2025.

Huh? A single Tesla Powerwall 3 stores just about the same 13.5 kWh the author describes as being the battery size they need [1]. And they are by far not the only ones offering ready-to-install battery packs.

Fully electric vehicles with vehicle-to-grid wallboxes enable even larger systems.

[1] https://www.tesla.com/de_DE/powerwall?redirect=no

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So this basically just shows that his solar panels are subsidized by the grid at whatever the depreciation rate is on 1000kWh of batteries.

which being very approximate is 15k gbp/year

If you don't live at some combination of high altitude, low latitude and low cloud cover then don't do this. You will never pay off the CO2 produced in making your installation. So it does more harm than good. This isn't true for all sites, but the large majority of where humans (especially English speaking humans) don't live somewhere where this type of setup doesn't do more harm than good.

Mexico City, Santa Fe, places like this are great for your proposed setup. Wherever you likely live, probably not.

That is a trick question designed to make people argue and feel like there is some science or math to it. There is not. Nobody here can accurately predict weather far out enough to be a factor in this decision. The truth will vary by demand by family which may have variability throughout the year or decade. Another variable is the number of cloudy days which will vary as climate changes.

The answer is somewhere in the neighborhood of as much as one can safely store and afford accepting that batteries have a short life. Much like wells in cold climates the batteries should be in an underground insulated vault made from higher quality concrete as to keep fire hazards away from the home. That is also where whole-home generators and fuel belong, in their own vault so they can be easily maintained without having to rent an excavator to dig out the tank.

Even on cloudy days you can generate power. Unless it is very thick clouds I generate enough for my base loads even in complete overcast skies because I have an "excess" of PV panels.

because I have an "excess" of PV panels.

Which aligns with as much as one can afford. If one calculated an exact amount they would not be able to get the results you are getting.

> "excess" of PV panels ... aligns with as much as one can afford.

does it? Panels are not the most expensive part of the system any more. Overcapacity of panels isn't the bottleneck any more. Battery capacity or roof space might be instead.