What Size Battery Does My Business Need?

A battery earns its keep by moving energy from a cheap moment to an expensive one. That means the useful size is set by how much energy you need to shift and how often. If your solar generates a large midday surplus that you cannot use until the evening, the battery needs to hold roughly that daily surplus. If your goal is to store cheap off-peak grid power for daytime use, size it to the daytime demand you want to cover.

Two businesses with the same annual consumption can need very different batteries, because one has a steady flat load and the other has sharp peaks. Half-hourly consumption data, ideally alongside your solar generation profile, shows the real shape to design around.

Your electricity tariff decides where the value is. On a time-of-use tariff with a big gap between peak and off-peak rates, a larger battery that shifts more energy into the expensive window can pay off. On a flatter tariff, the main value is storing solar surplus for later self-consumption, which points to sizing around your typical daily solar excess instead.

Export payments matter too. If you are paid little for export, storing surplus to use yourself is worth more, which favours a battery large enough to soak up the midday peak. If export is well paid, the case for a big battery weakens.

Batteries are rated by usable energy in kilowatt-hours (how much they store) and power in kilowatts (how fast they charge or discharge). Both need to suit your load. A battery that stores plenty but cannot discharge fast enough will not cover a sharp peak, so check the power rating against your peak demand, not just the energy figure.

Allow for the future. Rising demand from electrified heating or vehicle charging can change the picture, so it is sensible to design with some headroom or an upgrade path. Because the right size hinges on data and tariff, base the decision on a proper analysis of your metered usage rather than a rule of thumb.