Do I need a battery?

A battery is the question we are asked most often, and the one with the least straight answers online. The right answer depends on when your house uses electricity, and you already know that better than any installer. This guide helps you work it out.

What a battery actually does

Panels make power when the sun is up. Most homes use the most power when it is not: breakfast, and the stretch between five and ten at night. A battery takes the surplus from the middle of the day and holds it for those hours. It can also charge from the grid on a cheap overnight rate and run the house in the morning. That is the whole job. It does not make more power, and it does not take you off the grid.

Three questions about your own house

Answer these from memory. They are more reliable than any online calculator.

• Is someone usually home between ten and four?
• What runs in the evening: the oven, the dishwasher, a tumble dryer, electric heating, a car on charge?
• Does your supplier offer a cheap overnight rate, or could it?

If someone is home in the day

A good share of what the roof makes gets used as it is made: the kettle, the washing machine, a home office, the fridge and freezer ticking over. Solar alone can work well, and the case for a battery rests on the evening load and on whether an overnight tariff is available to you. For many retired households, panels first and a battery later is a sensible order, and every Essential system we fit has an inverter ready to take one.

If the house is empty until six

Without a battery, most of what the roof makes on a working day leaves the house for a few pence a unit, and the evening runs on full-price grid power. This is the household where a battery changes the result most. The battery fills by early afternoon and carries the house through dinner, the dishwasher and the evening television. For a working couple with a high bill, the battery is usually the part that makes the numbers work.

If you have an electric car or electric heating

These are large loads, and when they run matters. A car charged overnight on a cheap rate may not need the home battery at all. A car charged in the evening at full price will empty a home battery quickly, and the arithmetic changes. Electric heating runs most in winter, when the roof makes least, so in those months the battery works mainly with the overnight tariff. We model all of this at the survey using your real usage, and we tell you if a battery does not pay for itself.

How big a battery

Big enough to carry the house from sunset to bedtime, and no bigger. Capacity you never fill is money you do not get back. We size from your 12 months of usage, and we show you the forecast for two or three sizes so you can see where the extra capacity stops earning its cost.

What a battery will not do

• Power the house in a cut, unless you choose a system with backup for key circuits
• Take you off the grid: winter evenings still draw from your supplier
• Pay for itself on export alone; the saving comes from what you keep

The short answer

If someone is home most days and your evenings are light, probably not yet. If the house is empty on weekdays and busy at night, almost certainly. If you are in between, the survey settles it: we show you solar only and solar with a battery side by side, with your own usage behind both, and you choose.