How do you determine the right battery capacity?

Last updated: August 2026

The capacity of a home battery determines how much energy you can store for later use. Too small and you will not make the most of your solar power; too large and the investment takes longer to pay for itself. The right size follows from a few concrete figures in your own energy profile.

1. Start with your annual consumption and feed-in

Your annual statement shows how much electricity you use and how much you feed back into the grid. The part you feed back is usually solar energy that you were unable to use yourself at the moment it was generated. That is exactly the energy a battery can capture.

2. Look at the difference between purchase and feed-in rates

Energy you store yourself and use later does not have to be bought at the higher supply rate. The bigger the gap between what you pay when buying and what you receive when feeding back, the sooner a battery pays for itself.

3. Take efficiency and degradation into account

No battery is 100% efficient: part of the energy is always lost while storing and releasing it. In addition, a battery's capacity gradually decreases as it ages. A realistic calculation accounts for both.

4. Think beyond solar energy alone

Some battery systems can also be used to benefit from dynamic energy rates: charging when electricity is cheap and using it when it is expensive. That can shorten the payback period further, depending on your energy contract and how the system is controlled.

Calculate your own indication

Would you like to know which battery capacity suits your own annual consumption and feed-in? Use our battery calculator for an indicative calculation based on your own figures.

Open the battery calculator →