Battery capacity is measured in kilowatt-hours (kWh) — the same unit your electricity is billed in. A battery’s size determines how much electricity it can store.

Here’s what you need to consider:

1. Your Daily Electricity Usage

• Look at your electricity bills or smart meter app.
• The average UK home uses 8–10 kWh per day.
• If you only want to power essentials, you might only need 4–5 kWh of storage.

2. Your Solar Panel Output

• How much energy do your panels generate each day?
• A 4kW system in the UK produces around 10–14 kWh/day in summer, and 2–5 kWh/day in winter.
• You’ll want a battery that can capture your excess solar — not necessarily all of it.

3. What Do You Want the Battery To Do?

• Full home backup? You’ll need a larger battery (8–16 kWh+).
• Just cover the evening peak (4pm–11pm)? 4–8 kWh may be enough.
• Cover overnight electric car charging? Factor in your EV’s energy needs too.

🔋 Common Battery Sizes

Battery Size: What It Covers:

3–5 kWh

Evening lighting, some appliances for small homes or partial backup

6–8 kWh

Full evening use, small EV top-up for most average UK homes

10–16+ kWh

Full-day coverage, whole-home backup for large homes, heavy users, or full off-grid ambitions

🧠 Don’t Forget About Battery Type & Features

• Lithium-ion batteries are the most common — reliable, compact, and long-lasting.
• Some batteries (like Tesla Powerwall or GivEnergy) offer intelligent charge control to make the most of smart tariffs and weather forecasts.
• AC-coupled vs DC-coupled setups may affect how efficient or expandable your system is.

💸 Is a Bigger Battery Always Better?

Not necessarily! Oversizing your battery might mean:

• You’re paying for capacity you’ll rarely use.
• Your solar panels can’t fill it regularly (especially in winter).
• The payback period becomes longer.

That’s why matching your battery size to your lifestyle is key. It’s all about balance — not just going big for the sake of it.

🌞 Solar PV + Battery: A Smart Investment

Pairing your solar panels with the right-sized battery means:

• More solar self-consumption
• Less reliance on the grid
• More control over your energy costs
• Backup power during outages (depending on the system)

Even if you don’t have solar yet, a battery could still help you take advantage of off-peak rates and future-proof your home.