Battery storage
How Much Battery Storage Do I Need?
Battery capacity is measured in kilowatt-hours (kWh), the same unit on your electricity bill. Sizing one is more straightforward than most sales pitches make it sound, once you know what number you're actually matching it against.
Helpful video reference. Upvolt Energy's guide "How much Battery Storage do I need?" walks through the sizing logic in plain terms. Worth watching alongside this page.
1. Check your annual usage first
Before you look at any battery spec sheet, find your actual annual electricity usage in kWh. It's on your bill, or in your smart meter app. The UK average sits around 2,700 to 3,400 kWh a year for a typical household, but yours could easily be higher or lower depending on how many people live there and whether you're heating with electricity.
2. Size against your evening usage, not your whole day
A solar array does most of its generating in the middle of the day, when a lot of households are out at work or school. The battery's actual job is to catch the surplus you're not using then, and give it back to you in the evening when demand is highest and the panels have stopped producing. That means the number that matters is your typical evening and overnight usage, not your total daily figure.
Rough sizing by household
- 1-2 people, smaller solar array: 5-7 kWh usually covers it.
- 3-bedroom family home: 8-10 kWh is the common recommendation.
- Larger home, or planning an EV charger: 10-15 kWh, sometimes split across two units.
3. Bigger isn't automatically better
It's tempting to buy the largest battery on the price list, but a battery sized well beyond your daily solar surplus never actually fills up from your panels alone. You end up topping the rest up from the grid at full price overnight, which quietly defeats the point of having it. Match the battery to what your roof genuinely generates and what you genuinely use in the evening, not to a headline capacity number.
4. Battery chemistry matters for longevity
Most modern domestic batteries use LiFePO4 (lithium iron phosphate) cells rather than the older lithium-ion chemistry found in some early systems. LiFePO4 handles daily full cycles better over a 10+ year lifespan and has a lower fire risk profile, which is why it's now the standard recommendation for anything mounted inside or against a house.
When it's worth a proper survey instead of a guess
If you're adding an EV charger, running an electric heat pump, or you simply don't trust your own usage estimate, a proper survey using your actual half-hourly smart meter data will size a battery far more accurately than any rule of thumb on this page. We do that as part of an MCS-certified installation quote.
Frequently Asked Questions
What size solar battery do I need?
For a 1-2 person household with a smaller solar array, 5-7 kWh usually covers it. A 3-bedroom family home typically wants 8-10 kWh. Larger homes, or those planning an EV charger, often need 10-15 kWh, sometimes split across two units.
Is a bigger battery always better?
No. A battery sized well beyond your daily solar surplus never fully charges from your panels alone, so you end up topping the rest up from the grid at full price overnight, which defeats the point. Match capacity to what your roof genuinely generates and what you use in the evening.
What battery chemistry should I choose?
Most modern domestic batteries use LiFePO4 (lithium iron phosphate) cells rather than older lithium-ion chemistry. LiFePO4 handles daily full cycles better over a 10+ year lifespan and has a lower fire risk profile, which is why it is now the standard recommendation.