How Big a Battery?

A question we often hear at Tanjent is ‘How Big a Home Battery Do I Need?’ Or else ‘What home battery storage size is right for my family?’

Which IS a great question, just one that is not as straightforward as it would seem, to answer.

Most of us have never had battery storage in our homes or businesses before, so we have no prior experience to lean on. And whilst there are methods that will show what a solar array will produce over the course of a year (see, for example, How Much Solar Power Could My Roof Generate?) there isn’t the same ‘publicly available, free to use’ or ‘readily available’, software to measure battery usefulness.

How big a home battery do I need? (Image: Tanjent/DALL-E)

How big a home battery do I need? (Image: Tanjent/DALL-E)

The principal reason why it is a tricky question to answer, is that the energy consumption in our homes & businesses is very specific to that property, and it is that information which is key when calculating battery storage needs.

Using a Battery with Solar

For those with or planning to get solar panels it makes sense to consider the times when those panels are not generating electricity.

In the peak months of PV generation from April to August:

  • For a South facing solar array, PV generation has generally stopped by 7pm and starts to generate again by 7am.
  • For an East & West facing solar array, PV generation stops closer to 8pm, starting again from 6am.

If you can take meter readings corresponding to these times, this will give you a good indication of your evening energy consumption and therefore is a good starting point for a suitable battery storage size.

Using this method, if you calculated you were using 10kWh, and you may wish to take an average over a number of evenings, a 10kWh battery would likely suit you best.

For those also on time-of-use electricity tariffs (e.g. cheaper overnight rates), you may also wish to calculate your daily electricity needs in the depths of winter to guide you towards likely battery storage requirements.

If you are interested in exploring this further and finding out what size battery storage system would best suit you and your family, or your business, just ask Tanjent for a quote.

Our friendly team can be reached on 01923 537 535,  or even simpler, fill your details in here and we will contact you.

Update 2024: professionally installed batteries are now rated Zero for VAT, same as solar panels.