What size battery do I need for my solar panels?
(And should you even get one?)
Let’s face it — the idea of storing your own energy is pretty exciting. Energy independence, backup power in a blackout, and reducing those rising electricity bills? Yes, please.
But here’s the question we get asked a lot at Solar Advice Bureau: "What size battery do I actually need?"
So let’s break it down clearly — no fluff, no jargon, just what you really need to know.
Step 1: Understand your energy usage
Before even looking at battery sizes, the real question is, how much energy do you use, and when do you use it?
For example, a typical 3-bedroom home in the UK with 4 people uses around 8–10 kWh per day.
Some families use more in winter (due to heating and lighting), and less in summer — unless you have an EV, in which case, your usage jumps.
Tip: Look at your last 12 months of energy bills. Add up the kWh per month and divide by 30. That’s your average daily use.
Step 2: What does a battery actually do?
A home battery stores the excess energy your panels produce during the day so you can use it when the sun goes down — like in the evening or early morning.
This means:
- More self-use of your solar (less sold back to the grid)
- Cheaper bills (especially if you're on a time-of-use tariff like Octopus Flux or Agile)
- Backup power (some batteries offer this in power cuts — but not all!)
Step 3: So, what size battery do I need?
Here’s a general guide based on your daily energy usage:
If you generate more than you can store or use — the rest goes back to the grid (hopefully at a decent export rate). But if you undersize your battery, you’ll miss out on using more of your own free solar.
Step 4: Match battery to your solar system size
As a rule of thumb:
- A 3kW system often pairs well with a 5 kWh battery
- A 5kW system can benefit from a 10 kWh battery
- A 6.5kW+ system may need two 5–10 kWh batteries depending on your lifestyle
Bonus: don't forget about charging at night. With smart tariffs (like Octopus Go or Intelligent Octopus), some people charge their battery at night using cheap grid electricity, then use it during the day. This makes battery storage even more valuable — even when the sun isn’t shining.
So, is a battery worth it?
If you're home in the evenings or have high usage:
Yes. It helps you store the free power you generate and lowers your bill.
If you’re already efficient and use most of your power during the day:
Maybe. It depends on your lifestyle and if you’re chasing savings or backup power.
If you're not sure book a consultation with us. We’ll look at your bills, usage patterns, and help you decide what fits you best.
Final thought
A solar battery is not a one-size-fits-all deal. But if you get it right, it’s a brilliant upgrade to your solar setup. Not just for savings — but for peace of mind.
