A battery stores electricity so you can use it later, typically in the evening after the panels have stopped producing. The numbers on a battery specification can be confusing, so here is what the main ones mean.
Capacity is how much it stores
Capacity is measured in kilowatt-hours (kWh) and describes how much energy the battery can hold. It is the number most people look at first. Check whether the figure quoted is the total capacity or the usable capacity, because they are not always the same. A bigger battery is not automatically a better choice: it only helps if the solar array can fill it and the household can use what is stored.
Power is how fast it delivers
Power, measured in kilowatts (kW), describes how quickly the battery can charge or discharge. A battery with plenty of capacity but low power may not be able to run several appliances at once. When you list what you use in the evening, such as the oven, the kettle and the washing machine, you are also describing the power you need.
The inverter and how it is coupled
A battery stores DC, and a household uses AC, so an inverter has to sit somewhere in the chain. With a hybrid inverter, the panels and the battery both connect to the same unit, which manages the flow between them. With an AC-coupled battery, the battery has its own inverter and connects on the AC side. Which arrangement suits a property depends on whether the solar system already exists, on the equipment, and on where each unit can be placed.
Where the battery can go
Manufacturers set out where their batteries can be installed, including temperature limits, ventilation, clearances and access. The wiring regulations add their own requirements. A garage, a utility room or an outbuilding are common places, but each has to be checked against the product’s instructions before the position is agreed.
Settings that match the household
A battery is programmed as well as installed. It can be set to charge from the panels, to hold some energy in reserve, or on some tariffs to charge from the grid at certain times. The right settings depend on when the household is at home and on the electricity tariff, so they are worth discussing when the system is commissioned.
Planning something like this?
Tell us what you use in the evening and whether you already have solar panels, and email us a photo of the place you have in mind for the battery. You can read more on the battery storage page.