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

https://shkspr.mobi/blog/2025/09/how-big-a-solar-battery-do-i-need-to-store-all-my-homes-electricity/

I have a modest set of solar panels on an entirely ordinary house in suburban London.

On average they generate about 3,800kWh per year. We also use about 3,800kWh of electricity each year. Obviously, we can't use all the power produced over summer and we need to buy power in winter. So here's my question:

How big a battery would we need in order to be completely self-sufficient?

Background

Let's take a look at a typical summer's day. The graph is a little complex, so I'll explain it.

The yellow line shows solar production. It starts shortly after sunrise, peaks at midday, and gradually drops until sunset.

The red line shows how much electricity our home is using. As you can see, there's a large peak about 19:00 when we cook dinner.

The blue line shows how much electricity we draw or export from the grid. From midnight until sunrise we import because the sun isn't shining. Once the sun has risen we're able to power our house and export to our neighbours. When we cook, we draw from the grid and our battery - which is why the evening grid peak is lower than the household use dip.

The CSV of the data looks something like this:

Local_time

Household_(W)

Solar_(W)

2025-08-25T08:25:00.000+01:00

-187.76

1166.77

2025-08-25T08:30:00.000+01:00

-227.04

1193.25

2025-08-25T08:35:00.000+01:00

-253.06

1222.84

2025-08-25T08:40:00.000+01:00

-266.87

1245.18

2025-08-25T08:45:00.000+01:00

-450.8

1268.66

2025-08-25T08:50:00.000+01:00

-251.84

1281.79

2025-08-25T08:55:00.000+01:00

-1426.26

1306.93

2025-08-25T09:00:00.000+01:00

-206.78

1341.37

2025-08-25T09:05:00.000+01:00

-215.52

1390.9

2025-08-25T09:10:00.000+01:00

-242.6

1426.19

2025-08-25T09:15:00.000+01:00

-246.84

1473

It's fairly trivial to sum both columns and subtract one from the other. That shows either the excess or deficit in solar power for the household.

On that day, the house used 9.7kWh and generated 19.6kWh. I'd need a 9.9kWh battery to store the excess right? Wrong!

Because my usage doesn't track the sun, I'd actually need a 13kWh battery. That's the peak amount of excess electricity I've generated in that one day.

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.

Luckily, I have several years of real data to go off! Let's get started!

Disclaimer

This is based on data generated by my home battery. It has probes to measure solar output and grid flow. It is not 100% clock-accurate compared to my solar-panels' internal reporting nor what my smart-meter reports. I estimate a 1-2% deviation, which is good enough for these purposes.

My energy usage isn't representative of anything other than my usage. Your household is probably different. I already have a 4.8kWh battery which changes how and when I use energy.

This doesn't account for gas heating or hot water. We have some electric heaters and taps which increases our electricity usage.

My maths is probably right - but the code is open source, so feel free to check for yourself.

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.

Code

We tend to start generating more electricity than we use starting in Spring. So I've picked the end of March 2024 to the end of March 2025.

Let's see how big a battery we'd need to store our summer excess for winter. This finds the cumulative difference between each day's energy production and usage:

import osimport pandas as pd# Load all the CSVsfilepaths = [f for f in os.listdir(".") if f.endswith('.csv')]df = pd.concat(map(pd.read_csv, filepaths))# Make sure they're in orderdf = df.sort_values("Timestamp")df = df.reset_index(drop=True)# Resolution is every 5 minutes, so divide by 12 to get hourlydf["Cumulative_Difference"] = ( (df["Household_(W)"] + df["Solar_(W)"] ).cumsum() ) / 12# kWh of battery neededint(df["Cumulative_Difference"].max() / 1000)## Draw a pretty graphdf.plot(kind="line", x="Local_time", y="Cumulative_Difference", xlabel="Date", ylabel="MWh", xticks=["2024-04-01", "2024-05-01", "2024-05-01", "2024-06-01", "2024-07-01", "2024-08-01", "2024-09-01", "2024-10-01", "2024-11-01", "2024-12-01", "2025-01-01", "2025-02-01", "2025-03-01", "2025-04-01"], legend=False, grid=True, fontsize=15)plt.show()

The total is 1,068KWh - basically, a MegaWatt-hour of storage.

Here's a quick graph to show how the storage would be used over the year.

As you can see, even in this scenario there are a few days where we'd need to import energy from the grid.

Is this sensible?

Probably not, no. It doesn't account for increased energy use from having an electric car or moving away from gas heating / cooking. As solar panels increase in efficiency, it might be more sensible to replace the panels on my roof, or add some onto a shed.

The environmental impact of creating and storing such huge batteries could also be factored in.

A battery which is only 100% full for a few days probably isn't an efficient design. Using wind, hydro, and other green sources from the grid might be preferable.

But, remember, this is an exercise in wishful thinking.

Is this possible?

Grid-scale batteries exist and they work brilliantly.

But if I wanted my own MegaWatt-hour of battery storage, it would probably cost me between £100k and half-a-million quid.

That doesn't include maintenance, the land, planning permission, and a hundred other things.

But battery prices are falling fast. In the last decade lithium ion battery prices have fallen 90%. With new sodium ion batteries promising an even bigger drop - down to US$10/kWh.

If - and it is a big if - those numbers came to pass, it would probably cost around £8,000 for a domestic battery. Basically the same cost as adding solar panels in the first place.

Domestic solar works - yes, even in the rainy UK! It is relatively cheap, moves energy production as close as possible to energy consumption, reduces bill-shock, and means we don't have endless planning arguments about whether fields should be turned into solar farms.

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.

There's a bright and sunny future where every home can be solar-self-sufficient.

If you've enjoyed this blog post, please consider switching to Octopus Energy - we both get £50 when you join.

#solar

🆕 blog! “How big a solar battery do I need to store *all* my home's electricity?”

I have a modest set of solar panels on an entirely ordinary house in suburban London.

On average they generate about 3,800kWh per year. We also use about 3,800kWh of electricity each year. Obviously, we can't use all the power produced over summer and we need to buy power in…

👀 Read more: https://shkspr.mobi/blog/2025/09/how-big-a-solar-battery-do-i-need-to-store-all-my-homes-electricity/
⸻
#solar

🌞
Between the #solar panels and the battery, I've enough electricity to run the #airfryer for my lunch.

Is this #SolarPunk?

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Solar providing 1.27kW and battery providing 0.41kW. No electricity being drawn from the grid.

Your regular reminder not to use cheap #solar cables and connectors from random online stores.

Just helped someone diagnose a solar problem as "the cheap cable I bought melted in the MC4 connector and it's a good job it wasn't near anything flammable"

Most of those cables are not double insulated, badly crimped and rated at < 36v and often CCA not copper so not even high current carrying. They might look fine to the unfamiliar and you might think "it's only 800W" but that's enough for a fire..

What would it take for our home to be Solar Self-Sufficient?

Work in progress, but I think I have the answer.

🏠 I live in an ordinary house in suburban London.
☀️ Our solar panels generate 3,800kWh per year.
🔌 We use the same amount of electricity per year.

After crunching the numbers:

🔋 Capturing all our solar excess needs a 1 MegaWatt-hour battery.

#Solar #SolarPunk

Alt...

Graph of cumulative difference between solar production and electricity use. Starting at zero in March and gradually growing over 6 months, then descending to zero again.

🌞 🔋 Pakistan’s Solar Revolution Is Bringing Power to the People

Fed up with pricey electricity from an unreliable grid, Pakistanis have snapped up cheap solar panels. In an interview, Muhammad Mustafa Amjad, of Islamabad-based Renewables First, says his country can stand as a model for other nations as they transition away from fossil fuels.

#Solar #Energy #Pakistan #Climate
#Economy

https://e360.yale.edu/features/pakistan-solar-boom

#solar #solarpower #solarenergy

Ikea has started selling plug-in solar kits. No permits, no installers, full placement flexibility.

Currently they are only available in Germany but if it goes well they will start rolling them out in many more countries.

The system is small (800W) but that's enough to cover roughly 35% of a typical European apartment's daily electricity use.

> For one half-hour period on July 8, solar output was a record 14 gigawatts, meeting almost 40 per cent of Britain’s electricity demand during that period, according to the National Energy System Operator (Neso).

https://on.ft.com/4lyFl2K

#Solar

50% #recycled glass #solarpanel performs like brand new
#Solar panel recycler #SOLARCYCLE and Arizona State University proved solar panels made with recycled glass work just as well as new.
With Arizona State’s Ira A. Fulton Schools of Engineering, solar recycling company created prototype solar panel – called a “mini module”– using 50% recycled glass pulled from end-of-life solar panels. The mini module matched the performance of panels made entirely with new materials.
https://electrek.co/2025/08/01/50-percent-recycled-glass-solar-panel-performs-like-brand-new/

Canada is burning.

30 million hectares have burned in the last thirty months.

The Amazon, the world's 'other' lungs burned at a rate of 2 million hectares a year.

30 million hectares have burned in 🇨🇦 in the last thirty months.

Canada has NO Major Solar Project.
Canada has NO Major Wind Project.

Canada is the LARGEST PRODUCER OF CO2 On Earth.

#cdnpoli #Canada #shame #canpoli #carney #lpc #ndp #suzuki #build #solar #wind #tide

Alt...

A Canadian Capital city choking on cancerous smoke. Canada is the largest producer of CO2 on earth. Canada is Burning a Million HECTARES every month. Canada is burning 2,700,000 acres of first growth old trees EVERY MONTH

Alt...

Prime Minister Carney needs your loud demand to fight climate and fight fires and build solar and offshore wind, or our children die.

The forests of Canada are being turned to ash at a rate of a million hectares a month.

_________________________

Ontario Premier Ford didn't buy Water-bomber aircraft as he said, he lied.

Canada has no major solar or wind project.

A third (209) of the Climate Wild Fires Burning Are NOT being fought - 100's of thousands hectares.

_____________________

#CDNpoli #LPC #Carney #Wind #NewEnergy #Transition #Jobs #NDP #BCpoli #Build #Solar #Oil #Pipeline #Resistance #FN #FirstNations #EU #Klima

Alt...

The forests of Canada are being turned to ash at a rate of a million hectares a month ie-creek-fire-british-columbias-largest-ever-wildfire-remains-volatile-

Good news in hard times.

"Peak Energy just shipped the US’s first grid-scale sodium-ion battery"

Good news because we must transition off carbon fuels now, and good news because its not scarce or hard to mine, or behind some prick's tariff wall, its not dirty, won't burst into flames.

Because its salt. Like sunlight, its EVERYWHERE.

https://electrek.co/2025/07/30/peak-energy-us-first-grid-scale-sodium-ion-battery/

#climate #salt #grud #build #BuildFast #solar #wind

#Solar is now 41% cheaper than fossil fuels, new UN report finds: 'The sun is rising on a clean energy age' https://www.goodgoodgood.co/articles/solar-power-versus-fossil-fuels-cheaper-study #Solarpunk

Just noted... our #solar went live on 11th June, and as of today (just over a month later) we've just gone over our first 1MWh generated 😀

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Screenshot of part of the web UI of our solar inverter controller. Screenshot shows the text: Production 2.86 KW 16 Jul, 2025 10:26 AM 1.04 MWh Lifetime

SOLAR: yes, the tax credits are expiring at the end of the year (get started now!)

BUT... I was thinking how much #solar prices have dropped since I had mine installed in 2022 (catching the first wave of Biden's Inflation Reduction Act tax credits)...

1/n

https://drive.google.com/file/d/1I8HVaJ0GNHtVKeAHN--w4xAM6x5wElTV/view

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© Residential solar and storage prices both reach new all-time lows Solar prices dropped for the third six-month period in arrow, hitting $2.50 per watt, the lowest median quoted price since we began tracking data in 2014. Quoted storage prices also fell, setting anew record low of $999 per kilowatt-hour stored. In 2025, we are monitoring potential tariff impacts on solar and storage prices.

Those "free market" Republicans are trying everything they can to kill the green energy market — not just killing tax credits, but tariffs and they even proposed *taxing* solar (it failed).

Why? Why do they effin care so much?

The easy answer...

3/n
#climate #green #solar

New #blog post: Looking at changes in the UKs #solar capacity

After reading a post yesterday claiming that the UK's solar production jumped by 42% this spring, I had a look to see what our system achieved

Then, I fell down a couple of rabbit holes looking at changes in the UKs deployed capacity

https://www.bentasker.co.uk/posts/blog/house-stuff/looking-at-uk-solar-generation-changes.html

I was curious to see if this was true for us - https://www.ecowatch.com/solar-power-generation-uk-2025.html

> Solar farms and rooftops in the United Kingdom generated a record 42 percent more electricity from January through May 2025 than during the same period in 2024

Sadly (but not too surprisingly) it isn't, but between Jan - May this year our #solar generated about 18% more than it did the year before

So increased sunshine is definitely a factor, but most of the gain in the article was prob expanding capacity

Alt...

During Jan - May 2024 we generated 996 kWh of electricity. In the same period this year, it was 1200.

A year into having home #solar, the numbers are in!

45% of our annual household consumption was generated by the solar system (in rainy Northern Ireland), though we were only able to use 33% due to having no batteries. 33% represents a saving of over £1000 on energy costs.

gemini://s73.girv.in/glog/2025/2025-07-01-solar-stats-062025.gmi

https://s73.girv.in/glog/2025/2025-07-01-solar-stats-062025.html

☀️

One of Europe’s Hottest Cities Rediscovers an Old Cooling Technique

By Laura Millan
August 8, 2023

"The streets of #Seville in southern #Spain were so hot that July afternoon that it felt almost impossible to walk outdoors. As temperatures approached 42C (108F), people scrambled to find shelter in air-conditioned homes, offices and public buildings. Yet, less than two miles from the city center, a cool breeze blew under a giant white roof.

"The structure is a part of CartujaQanat, an architectural experiment in cooling solutions that doesn’t rely on burning more planet-warming #FossilFuels. The site, about the size of two soccer fields, includes two auditoriums, green spaces, a promenade and a shaded area with benches. But its star performer remains hidden — the qanat, a network of underground pipes and tubes inspired by Persian-era canals.

"The grid of #aqueducts can lower surrounding temperatures by as much as 10C using just air, water and #solar power, according to Emasesa, the Seville public water company that helped to build it. The system is modeled on ancient tunnels dug to bring water to agricultural fields that were first documented in what is today #Iran. The Persians realized 1,000 years ago that the running water also cooled the air in the canals, so they fashioned vertical shafts to bring that air to the surface.

" 'This is not an air-conditioning system like the one you may have in your home,' says Juan Luis López, the project’s supervisor and an engineer at Emasesa. 'We use natural techniques and materials to reduce temperatures.' "

Read more:
https://www.bloomberg.com/features/2023-seville-spain-extreme-heat/

Archived version:
https://archive.ph/36fz1

#SolarPunkSunday #History #PersianTechnology #ClimateChange #KeepingCool #ExtremeHeat #AncientTechnology

Batteries are so cheap now, #solar power doesn’t sleep https://electrek.co/2025/06/20/batteries-are-so-cheap-now-solar-power-doesnt-sleep-ember/

As of yesterday, our house in London has exported *one MegaWattHour* of solar electricity.

All of our neighbours benefit from clean, green, locally generated power.

We have a small roof, with an east/west split, and yet #solar works brilliantly.

More details:
https://shkspr.mobi/blog/2025/03/what-does-a-personal-net-zero-look-like/

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Graph showing a peak in summer.

#solar and #battery installation at a relatives house did well for #resilience - a cable break cut off the #UKPN grid feed for around an hour - whole house remained with #power from the #renewable #energy sources, the battery reserve was barely touched due to good sunlight (the people in the house didn't even need to switch off high consumption equipment, although I had suggested this should the power cut have lasted any longer (the grid supply returned around an hour later) #electricity

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Victron VRM real time display showing a large country house being entirely supplied for its energy requirements by solar and battery (due to the incoming grid power being lost)

And #HeatPump install all booked in!

If it all goes to plan, we'll have both #Solar and #HeatPump in before the end of the month 😳

Now for my sanity I may regret doing two installs back to back, but at least it’ll be done quickly!
#HeatPump #Solar