How big a solar battery do I need to store all my home's electricity?

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.

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.

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

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.

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.

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...

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.

Keep in mind that the UK is really far north, much farther north than most people expect, really, and the nights are really long in winter (there's up to 16 hours of night in London in December). And even your daylight hours aren't going to be sunny in average

So you'd have to over-provision a lot (like 10 or twenty times).

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.

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.

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

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.

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.

What about installation? DIY?

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.

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

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.

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.

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.

My detached house has less space for solar panels than some smaller homes because all faces of the hip roof are triangular; lots of houses nearby that are semi's or terraced actually end up having more roof space because their roof faces are rectangular.

I managed to have 14x 465W panels total added on the east and south faces of my home, but the installer wanted an extra 40% of the total system price to add 5 more panels (and the 15th they couldn't fit on the south face, for 6 total on the west) because they'd have had to erect additional scaffolding and who knows what else. That was an absurd additional cost so we didn't do it, but that additional generation late into the afternoon would have been great for our peak usage at dinner time. My suspicion is they simply didn't want to do it, because the cost just doesn't add up.

On an overcast day at this time of year I can generate nearly enough to power the "baseline" of the house, but currently I receive 24p/kWh to sell the energy back, and I can charge the batteries at 15p/kWh over night, so I can break even if I can generate just enough to export to cover the night-time charge of the batteries.

I haven't had them long enough to run through winter yet so we'll have to wait and see, but based on the end of this summer, I could probably cover the winter usage with export payback through summer at the current tariff rates when we were generating about 100% more than we were using per day.

I suspect the introductory tariff is far more generous than I'll have access to in a year's time when it expires though.

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

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.

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.

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.

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.

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.

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

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.

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

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

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

It was actually 1000 times that much.

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

Model 3 or Y with 70-80KWH capacity battery ~~ $40-50,000

Powerwall price: ~$15,000 for 13.5 kwh storage.

You're paying around double for a fancy case and the UI.

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

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

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.

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

I grew up in Australia used to a grid averaging perhaps an hour’s downtime in the typical year. But now I live in India, and not only is the power frequently off for hours at a time (it’s a rare week that lacks an hour of downtime, and five or ten hours isn’t uncommon), the quality of the power is also far lower, and it damages hardware. It’s normal for AC units to need mildly expensive component replacements every year or two due to electrical damage, even with the obligatory voltage regulator in place, whereas in Australia I think most people never need to professionally service their AC until it completely packs up after maybe 15 years. If you’re going to want a decent-sized inverter and batteries anyway to get reliable power, then so long as you can get enough solar panellage, getting those solar panels and more batteries and going off-grid becomes mighty attractive—I suspect a payoff period of under a decade, even with comparatively cheap grid power, partly on the strength of electronics living longer.

—⁂—

Somewhere along the way, it actually becomes mandatory to be connected to such services. In Australia I lived in a rural town of under 100 people, and I asked if I could disconnect from the town water supply, and was told no. So that was some sum of mandatory daily connection fee for something that I would have preferred to unsubscribe from. (Town water was only hooked up to some outdoor taps, and the toilet; the supply had only become treated/potable five years prior, so every house was still hooked up to their rainwater tanks. In fact, the guy I bought the place from said that twenty years earlier you didn’t use the town water on your garden because it would kill the plants.)

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. )

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.

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.

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.

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

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.

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.

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.

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.

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).

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

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

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.

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

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

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.

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

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

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.

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".

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.