Basically why the grid exists to begin with. You're not supposed to be solving these engineering problems on a household budget inside a single home.

You'd be better off simply reducing your consumption or finding alternative methods of power (nat gas or maybe wind or geothermal) during the longer winter nights.

If you really want to go crazy, you should consider investing in a bigger home with better insulation and roommates. An apartment/condo block can at least leverage economies of scale, if you're dead set on DIY. More people benefiting from the setup dilutes the cost per person.

Something very important that anti-nuclear but otherwise environmental minded people should realize is this sentence: " There's no practical way to build domestic batteries with this capacity using the technology of 2025."
Also applies to grid storage. There does not exist a chemical energy storage solution that can substitute for "baseload" power. It's purely theoretical much like fusion power. Sure maybe in 50 years, but right now IT DOESN'T EXIST. Economically, practically, or even theoretically.

Why do I bring this up? Because I've seen too many people think that solar and wind can replace all traditional power plants. But if you are anti-nuclear, you are just advocating for more fossil fuels. Every megawatt of wind or solar, has a megawatt of coal or gas behind it and thus we are increasing our greenhouse gas emission everytime we build "green" generation unless we also build Nuclear power plants. /soapbox

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.

I mean, I think that it's probably not a good idea for this guy to try to go fully off-grid if he has access to the grid, but for the sake of discussion, if one were honestly wanting to try it and one is in the UK, I'd think that one is probably rather better off adding a wind turbine, since some of the time that the sun isn't shining, the wind is blowing.

https://www.statista.com/statistics/322789/quarterly-wind-speed-average-in-the-united-kingdom-uk/

Wind speed averages in the United Kingdom are generally highest in the first and fourth quarters of each calendar year – the winter months.

The UK is one of the worst places in the world in terms of solar potential:

https://globalsolaratlas.info/

But it's one of the best in terms of wind potential:

https://globalwindatlas.info/

Guessing it would be more practical to have enough solar panels to fulfill energy needs in winter.

Factorio has prepared me for þis challenge...

Author's diagram is about summer. Fall, winter, spring is about heating-degree days. If you're heating your home with electricity, you'll not get there with batteries.

So, working towards a solution, there are other ways to store excess energy than in batteries. One example is sand, which can be heated to very high temperatures. Insulate a sand container well and its storage can do a lot of home-heating.

Example: https://www.livescience.com/technology/engineering/a-scalding-hot-sand-battery-is-now-heating-a-small-finnish-town

We'll need to put a lot of different methods into use. There are many practical ideas out there, and they'll need to be tried.

It's practical for someone with limited space for panels on a small room, but I ran these calculations by moving almost all loads to daytime, sizing the panel array to the (minimum daily usage + efficiency losses) * buffer factor for days long storms or equipment failure.

Start with the comparitively cheap panels if you have the space, move electrical loads to the daytime and design the house for thermal momentum, and size storage to the minimum inclusive efficiency losses times buffer. If you have the roof space the panels are the cheapest part and you should usually way, way over panel.

The most important thing is having thermal mass enough or living in a climate that allows your home to not need thermal input or extraction at night. Heat is expensive and exponentially moreso if you need to produce it from conventional storage.

battery and solar at the home level is what makes the most sense.

60% of the planet lives between the subtropics and tropics. There is way more than plenty of sunlight hitting our earth to support all of our energy demands, and any naysaying around battery technology is missing the forest for the trees.

There was an article posted somewhere on Lemmy a few months back where someone tried to do similar calculations for the US as a whole. What I took from the result was 95% renewable was achievable and still cheaper than fossil fuels. However the over provisioning of renewables and over double the storage needed to reliably achievable 100% made that infeasible with today’s proving and technology. Basically you can install storage to cover when the sun is not shining but it’s much more difficult to cover weeks of gloominess

We have a whole home generator that runs in natural gas. They’re not the quietest things. Been tossing around the idea of having batteries added so that when the power cuts we go to battery. Then when the battery gets low the generator cuts on just long enough to charge the batteries. Wash rinse repeat.

1. Is HVAC excluded?
2. Do you have an EV?

With an EV you can have 80%-90% of days covered, and top up with EV. You also get to dump daily surpluses into EV, and you can think of covering winter heating with solar and a heat pump. Easier if you have a fireplace for extreme cold possibility.

Storing heat with fall surpluses is path to get winter heating covered. Heat pump can make hot water very efficiently, and resistance heating can make a pile of dirt 300+C. Radiant floor heating is most efficient because water is distributed around 30C. This means your 90C water volume is 60C effective heat storage that is generated at 600% efficiency in fall, and 300% efficiency in typical UK winter, and your dirt heat storage can be 5x more dense.

A 2nd EV even if not frequently used during the day can be an attractive option, especially if used, and tax credits will go away soon, or have gone away (makes used prices lower) can be much easier than home batteries, and much cheaper if it remains uninsured/unused, and resale value doesn't go down much because of few miles driven. Where utility service includes a high fixed monthly charge, ($50/month in Toronto), $12000 over 20 years savings creates high incentive to remove electric utility. Gas utility has similar fixed vs variable equation, but for Toronto, heat is somewhat reasonable from high supply on our continent.