Home Battery Capacity: The right capacity for your home
5, 10, 15 or 60 kWh? The right size depends on your consumption, your solar surplus and what you want the battery to do. This guide walks you through it step by step.
- Independent advice
- 3-60+ kWh covered
- Free sizing tool
In short
Size the battery to the electricity you use in the evening and at night. That is the hard ceiling on what storage can ever save. For most households without an EV or heat pump that lands between 5 and 10 kWh. With an EV or heat pump, 10 to 15 kWh. Above 6,000 kWh per year, 15 to 25 kWh.
Tip from Mike, editor
Capacity matters, but the platform matters more. Pick a brand that lets you add modules later. Your energy use will change when an EV or heat pump arrives, and swapping a whole system is expensive.
What does capacity mean?
Capacity is how much energy a battery can store, in kilowatt-hours (kWh). It says nothing about how fast that energy can go in or out. That is power, in kilowatts (kW), and it is set by the inverter.
Think of a swimming pool. The volume of the pool is capacity in kWh. The pump that fills and empties it is inverter power in kW. A big pool with a small pump still empties slowly.
Capacity only pays for itself if it actually gets used. A battery that is full by 2pm and empty by 9pm still leaves you buying expensive evening electricity for half the night. Getting the size right is less about buying as much storage as you can afford, and more about matching it to how your household uses electricity after the sun goes down.
Recommended capacity per household
Four things set the real answer: your total annual consumption, how much of that falls in the evening and at night, whether an EV or heat pump is already in the house or on the way, and how much solar you have to recharge from during the day. As a starting point:
| Annual consumption | Situation | Recommended capacity |
|---|---|---|
| Under 2,000 kWh | One or two people, small apartment | 3-5 kWh |
| 2,000-4,000 kWh | Family, no EV or heat pump | 5-10 kWh |
| 4,000-6,000 kWh | Family with an EV or heat pump | 10-15 kWh |
| Over 6,000 kWh | Large family with EV and heat pump | 15-25 kWh |
These are indicative ranges. Your evening and night consumption sets the real number, so run the configurator below for a figure based on your own data.
Too small or too large
Getting the size wrong rarely means the system stops working. It just quietly costs you money, in one of two directions.
Too small
- Fills within a few sunny hours and exports the rest anyway
- Empty before midnight, so you still buy peak electricity
- Fixable later if the system is modular
Too large
- Rarely fully charged, especially in winter
- You paid for capacity that never cycles
- Extra modules add standby consumption
Should you choose a modular system?
A modular battery lets you start small and add modules later. That is useful when your budget is limited, your future consumption is uncertain, or an EV charger or heat pump is planned.
Check before you buy
- Is expansion officially supported, and up to how many kWh?
- Must added modules match the age, capacity or firmware of the first?
- Does the inverter have headroom for the extra power?
Done well, it also means you are not paying today for capacity you will not need until that EV or heat pump actually arrives.
Frequently asked questions
What is the difference between nominal and usable capacity?
Nominal is what the label says; usable is what the battery management system releases. Divide the storage you need by the usable percentage: 9 kWh needed at 90% usable means roughly 10 kWh nominal.
How much battery per kWp of solar?
A rough starting point is 1 to 1.5 kWh of storage per kWp installed. It is only a starting point. Your consumption pattern matters more than the ratio.
Does winter change the answer?
Yes. Sizing on peak summer production gives an oversized system. Use a full twelve months of data, which is exactly what our hourly model does.
Why not just buy the biggest battery I can afford?
Beyond the point where it covers your evening and night use, extra capacity rarely cycles. You end up paying for kWh that sit idle most of the year, when that budget is often better spent on more solar, a heat pump, or simply saved.
Get the size for your own home
The calculator uses your consumption, your solar export and your local tariffs to recommend a capacity, and shows the payback that comes with it.