What is the best storage capacity of a home battery for your family?

When purchasing a home battery, you should choose one with a capacity – i.e. the amount of energy that can be stored in the battery – that is suitable for your situation. This depends on three factors, which are set out in more detail below. 

A home battery allows you to temporarily retain the solar energy you have generated during the day but do not use immediately, so that you can use it at night for your fridge or freezer, for example. When choosing the storage capacity of a battery, you should remember that bigger is not always better. It’s important to choose a home battery with a capacity that corresponds at least to the power output of your solar panel system, your family’s average consumption between sunset and sunrise, and your future energy consumption.

If you choose a battery with insufficient capacity, you cannot store all energy generated by your solar panels. Any self-generated energy that you cannot store is transmitted to the grid, which means that you may have to buy energy when the sun does not shine. If your battery has too much capacity, your solar panels will often be unable to fully charge the battery or the energy stored is not fully consumed in time. You will have paid too much for your battery and you will also miss out on the compensation for surplus electricity supplied to the grid. In both situations, your investment in a home battery does not provide the best possible return.

The conclusion is that the storage capacity and the power output of your solar panel system should be well-balanced, which you can achieve if you have 1 to 1.5 kWh of battery capacity per kWp of solar panels. This rule holds true if your annual energy production roughly corresponds to your annual energy consumption.  

You should also consider your consumption when choosing the most suitable storage capacity for your needs. Ideally, the energy you want to use during the day is immediately generated by your solar panels. To increase your self-sufficiency, you could use solar energy stored in a home battery for your consumption at night. This requires a battery that has sufficient capacity to cover that consumption. The amount you generally consume between sunset and sunrise can be estimated using the data from your digital meter or the app you use to monitor your consumption. Do note that you may need to draw on your battery during the day on days with less sunshine, in which case the energy stored in your battery will not be sufficient for your nightly consumption. 

As a home battery is an investment you make for the next ten to twenty years, be sure to consider a possible future increase in your electricity consumption. If you were to install a heat pump or a heated pool, for example, it would be better to opt for some extra capacity or a system that can be expanded over time.  

If the above information has helped you determine how much energy you should approximately be able to store in your home battery and how much energy you would want to get from your battery, feel free to request information about the available models. Bear in mind that there is a difference between the ‘usable’ and the ‘total’ capacity of a home battery. Depending on the type or the technology used, the total storage capacity of the battery cannot be fully used at all times. The usable capacity reflects the actual storage size and is expressed as a percentage of the total energy capacity. You can find the relevant value in the manufacturer’s technical data sheet. In some cases, you will see the terms ‘usable energy’ or ‘depth of discharge’ (DoD). If this information is not specified on the data sheet, you can reasonably assume that the stated capacity is the usable capacity.

As there are quite some aspects to consider when determining the suitable storage capacity and choosing the right type of home battery, we recommend that you engage the expertise of an experienced installer.