The short answer
Most UK homes with solar panels need a battery of 5 to 10kWh. That’s usually enough to store the spare solar power you make during the day and use it in the evening, when electricity use peaks.
The right size for you depends on three things: how much electricity you use, when you use it, and how big your solar system is. An electric car, a heat pump or a cheap overnight tariff can push the ideal size up to 15kWh or more.
As MCS-certified installers, we’ve fitted batteries from 5kWh to 24kWh across London, Essex, Kent and the South East. Here’s how we work out the right size, and how you can get a good idea yourself before we survey.
How to work out the right battery size
1. Check how much electricity you use
Look at your last 12 months of energy bills, or your energy supplier’s app, and find your yearly electricity use in kWh. Ofgem says the typical British household uses around 2,900kWh of electricity a year (Ofgem). That works out at roughly 8kWh a day.
2. Work out how much you use after dark
A battery earns its keep by covering the hours your panels aren’t producing: evenings, overnight and early mornings. In most homes, around half of daily electricity use falls in those hours. If you use around 8kWh a day, about 4 to 5kWh of that is after dark, so a 5kWh battery would cover it on most days.
If you’re out at work all day and home in the evenings, more of your use falls after dark, and a slightly bigger battery makes sense.
3. Match the battery to your solar panels
There’s no point in a battery your panels can’t fill. A typical 4kWp system can comfortably fill a 5 to 10kWh battery on a bright day, but production drops a lot in winter. Our guide on whether solar panels work in winter explains why.
As a rule of thumb, we size the battery so it fills on most days from spring to autumn. That gives you the best return without paying for capacity that sits empty.
Solar battery size guide
Use this as a starting point. Your survey will confirm the right size from your actual usage.
| Your home | Typical battery size |
|---|---|
| Flat or 1-bed house, 1–2 people | 5kWh |
| 2–3 bed house, 2–4 people | 5–10kWh |
| 4+ bed house, 4–5 people | 10–15kWh |
| Any home with an electric car or heat pump | 15–24kWh |
What can change the answer
An electric car. Charging an EV can easily double a home’s electricity use. A bigger battery lets you store more solar power for charging, or charge the battery overnight on a cheap rate and use it the next day.
A heat pump. Heat pumps use most of their electricity in the colder months, when solar output is lowest. A battery won’t run a heat pump on solar alone in winter, but a larger battery charged on a cheap overnight tariff can cut running costs a lot.
A time-of-use tariff. Some energy tariffs offer much cheaper electricity overnight. With one of these, your battery can charge from the grid at the cheap rate in winter and from your panels in summer. That’s why a bigger battery can pay off even if your panels are modest.
Your plans. If you’re thinking about an EV or a heat pump in the next few years, tell us at survey. The Fox ESS and Sigenergy systems we fit are modular, so you can start with what you need now and add capacity later.
The batteries we fit
We fit three main battery brands, chosen for reliability, warranty support and how well they suit UK homes:
- Fox ESS: modular batteries you can add to as your needs grow. We’ve completed the Fox ESS installer programme, and Fox is our most popular choice for new solar and battery systems.
- Sigenergy: a modular, stackable system that suits larger homes, and homes planning for an EV or heat pump.
- Tesla Powerwall: a single 13.5kWh unit with a well-known app, popular with homeowners who want a premium all-in-one battery.
Already have solar panels? You can usually add a battery without replacing your system. Read our guide: Can I add a battery to my existing solar panels?
Frequently asked questions
Is a bigger battery always better?
No. A battery that rarely fills up costs more without saving you more. The right size is one your panels (or a cheap overnight tariff) can fill on most days, and that covers most of your evening use.
Is a 5kWh battery enough?
For a smaller home, or a couple who use around 2,000 to 3,000kWh a year, a 5kWh battery often covers most evening use. Larger families usually benefit from 10kWh or more.
Can I add more battery storage later?
With a modular system like Fox ESS or Sigenergy, yes. You can add battery modules as your needs change, for example when you get an electric car.
What does “usable capacity” mean?
It’s the amount of stored energy you can actually use. Batteries keep a small reserve to protect their lifespan, so always compare usable capacity, not the headline figure. We quote usable capacity on every proposal.
Do I need a survey to size a battery?
Yes. We look at your electricity use, your roof and existing panels, your fuse board and where the battery will go. We aim to survey within 48 hours of your enquiry.
Get the right battery for your home
Eco Systems Group has been installing energy improvements since 2012. We’re MCS-certified for solar panels and battery storage, and our own installation teams fit systems across London, Essex, Kent, Surrey, Hertfordshire, Norfolk and the South East.
Tell us about your home and we’ll recommend the right battery size, with no obligation. Call 0203 411 4885 or request a free quote.
