What size solar battery do you need? A 2026 guide

• We’ve independently researched and ranked the top solar storage batteries, and we’re here to help you choose the right size for your home, budget and solar panel system
• Storage battery capacity ranges from 1kWh to 13kWh, and the average cost is £4,500
• A typical three-bedroom UK home needs at least an 8kWh battery – but we recommend buying a slightly bigger unit

The size of the solar battery you need depends mainly on how much energy your household consumes. For an average three-bedroom UK home with solar panels, we recommend at least an 8 kilowatt per hour (kWh) battery to ensure that you’re covering your daily energy usage. We suggest going bigger if you can afford it – 10kWh would give you additional capacity for off-peaking grid charging and particularly sunny summers.

Once you know the size you need, check out our guide to the best solar batteries currently available. We analysed dozens of available batteries to whittle it down to our top eight based on value for money, usable capacity, depth of discharge, temperature resistance, compact size, warranty, lifespan and scalability.

For now, read on to expand your understanding of usable capacity versus total capacity, the impact electric vehicles (EV) and heat pumps have on solar batteries, as well as the answer to the all- important question: What size solar battery do you need?

What size solar battery do I need? At a glance

Strapped for time? Here’s our recommendation for minimum solar storage battery sizes, based on the size of your household:

What size solar battery do I need?

To work out what size battery you’ll need, start by calculating your electricity usage. Look at either your smart meter or your monthly energy bills – to account for fluctuations, we’d recommend taking an average of the past three months.

Next, divide by thirty to get a rough estimation of your daily energy usage.

So let’s say you use 225 kWh of energy on average every month (the norm for a 3-bed household in the UK). Divide that by 30 and you get around 7.5 kWh, which means you’ll need an 8 kWh battery at the bare minimum to cover your daily energy usage needs.

This is what we call the 1:1 approach – it removes the variables (sunlight/peak usage hours, solar panel output/efficiency, smart tariff usage, budget) and gives you the simplest possible equation for choosing the right solar storage battery for you.

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Interview with a solar panel owner

How big is your solar panel system, and how roughly much did it cost?

“We had a combined package of solar panels and solar batteries, with a capacity of 13.8 kilowatts (kW). The total cost was £14,500. The panels were about £5,000.”

Do your solar panels generate enough power to cover all your electricity needs?

“In June, which was sunny, we used solar for almost all our electricity needs, including the car and hot water. In July and August, we had to use some grid power overnight to charge the batteries because the weather wasn’t so good.”

Have you managed to break even on your solar panels?

“We won’t break even for a few years yet, but feel we have pre-bought our energy and are protected from the vagaries of the energy market.”

Read Kassy's full interview

Kassy Homeowner

Kassy lives in North Yorkshire, and has owned solar panels and solar batteries since February 2023.

What size solar battery do I need for solar panels?

If you want to match your solar storage battery to the output of your existing solar panel system, you don’t need to perform any complex calculations – our simple rule-of-thumb guide will do:

We give a range here because we’re taking into account usable capacity, which means you’ll want to allow about 1kWh extra for your solar storage battery.

What is usable capacity (Depth of Discharge)?

Battery sizes are measured by their capacity to store electricity (in kWh), but it’s important to consider usable capacity rather than just what the total capacity is.

That’s because you don’t want to actually use a battery’s entire capacity, as this can damage it. The usable capacity is called depth of discharge (DoD), and most modern batteries have a DoD of between 90 and 95%.

Here’s how some of our top-rated solar storage batteries compare, from a usable capacity perspective:

As you can see, some modern batteries can discharge their entire capacity without any negative effects.

What are battery cycles?

A storage battery’s cycles means how many times it can be charged and discharged — a greater number of cycles is better because you can use your battery more before it starts to degrade.

Your battery’s warranty is typically connected to how many cycles it has, though many newer batteries offer time-specific warranties with unlimited cycles, such as the Tesla Powerwall 2.

There are also throughput warranties available, which are measured by the total energy guaranteed to pass through the battery. This has advantages over number of cycles, as it more accurately reflects energy usage.

What size solar battery do I need for EV chargers and heat pumps?

Having a heat pump or EV charger will significantly change your battery’s requirements because both a heat pump and an EV significantly increase your home’s energy usage, therefore increasing the size of the battery you need (remember the 1:1 approach?).

An EV draws substantial power (about 7.2kWh) and a heat pump will draw about 10kWh daily, and more in the winter. If you have both an EV charger and a heat pump, you should definitely think about buying a bigger battery.

Should I buy a large solar battery or a small solar battery?

Large and small are relative terms, but we always recommend buying a slightly oversized solar battery, if you can afford it. If you’re using a Smart Energy Tariff that allows your battery to draw from the grid at off-peak times, you’ll be glad for the extra capacity, and you stand to benefit during the long summer months – when your solar panels are working overtime – as well.

In addition, we think it makes good sense to plan ahead – buy an oversized battery if you don’t currently have a heat pump or EV but intend to purchase either one later.

In other words, it’s better to have a battery that’s slightly too big than slightly too small. We only suggest buying an undersized battery if you lack the space or funds – even if your daily energy usage is low, it still pays to buy slightly bigger.

One thing to note, though, is that many modern solar batteries can be expanded with additional units. Brands such as Bluetti use a modular design where you purchase a base unit and then you can add additional battery modules on top later.

Similarly, the Tesla Powerwall 3 can be expanded, although it will require you to add a new, full-sized battery unit alongside your first one.

Can I have multiple storage batteries?

Yes, but there are caveats. You’ll struggle to fill multiple batteries without a large solar panel system.

There’s also the risk of one or several batteries failing in a multi-battery system, which can reduce the overall effectiveness and how much power you can access.
You’re typically better off sticking to one or two larger batteries, as a single larger unit often offers better system integration and a more streamlined warranty, potentially making it more reliable.

What size battery do I need to go off-grid?

You’ll need either multiple batteries or one large battery to go off-grid, but even then you might not be able to go completely off-grid. Actually going fully off-grid requires multiple renewable energy sources to guarantee you can charge your batteries, and these batteries need enough capacity to provide power 100% of the time.

Consider pairing a solar panel system with a small wind turbine or if the environment permits, a small-scale hydroelectric system to charge your battery. This is because the sun will not always shine bright enough to charge your battery optimally, and having a backup energy source helps ensure your battery has enough charge at night.

Can you use a solar battery to charge an electric car?

You can charge an electric car with a storage battery, but it’s typically not worth it because you’ll almost certainly need to tap into the grid to finish charging.

You’ll need either a battery with a very large capacity, or multiple batteries. This is due to the high energy demand, as the typical capacity of an electric car battery is around 40 kWh.

It’s much better instead to use your solar panel system or the grid to charge your electric car directly, and save your storage battery for other uses.

Summary

• We recommend calculating the size of solar storage battery you need based on either your daily energy usage or the number of solar panels you have (or both)
• Remember: it’s better to buy an oversized battery than an undersized one
• You can have multiple storage batteries, as long as you have a solar panel system big enough to charge them
• If you have an electric car, you can use your solar battery to charge it, but it’s typically not worth it. You’ll almost always end up using the grid to fully charge your electric vehicle
• Consider your power usage, how powerful your solar system is, battery cycles, and whether you plan to go off-grid when thinking about purchasing a solar battery

Written By

Tom Gill Writer

Tom has been writing for The Eco Experts for nearly five years an in that time, he has calculated the carbon footprint of the Roman Empire, profiled the world’s largest solar farms, and investigated what a 100% renewable UK would look like.

He has a particular interest in the global energy market and how it works, including the future of hydrogen, and Cornwall’s growing lithium industry.

Tom also regularly attends Grand Designs Live as a Green Living Expert, where he provides expert solar panel advice to members of the public.

He frequently focuses on niche environmental topics such as the nurdle problem, clever ways to undo the effects of climate change, and whether sand batteries could store enough energy for clean heating in the winter.

If there’s an environmental niche to be covered, it’s a safe bet Tom’s already thinking of how to write about it.

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Reviewed By

Tamara Birch Newsletters and sponsored content editor

Tamara is a journalist with more than six years experience writing about environmental topics. This includes advising small businesses on cost-effective ways tom become more sustainable, from installing to solar panels and heat pumps and reducing waste. She has used her journalist and research skills to become highly knowledgeable on sustainable initiatives, issues, and solutions to help consumers do their bit for the environment – all while reducing monthly costs. Now, she’s using this experience to advise homeowners on the benefits of installing low-carbon technologies. She is also qualified in offering innovative initiatives to improve sustainability practices in businesses, from advertising to marketing and publishing.

Her passion for sustainability and eco-friendly solutions stems from a long obsession with nature and animals and ensuring they feel looked after. In her free time, Tamara enjoys reading fantasy novels, visiting the gym, and going on long walks in new areas.

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