Battery storage projects

Sizing it around real usage

The commonest mistake with storage is buying by the biggest number available. A battery only earns its keep on the cycles it actually completes, so one sized well beyond a household's overnight demand spends much of the year part full and never pays back the extra capacity. The useful figure is what the property draws between sunset and sunrise, which a year of half hourly data or a smart meter will tell you.

For most homes the honest answer is a good deal smaller than expected. Properties with electric heating, a heat pump or an electric car are the exception, because they shift far more consumption into the hours when a battery is the only thing generating anything.

Retrofitting to an array you already have

Adding storage to an existing solar installation is routine, and the question is normally which inverter arrangement to use. A hybrid inverter replaces the existing one and handles both jobs, which is neater and usually more efficient. An AC coupled battery sits alongside what is already there and leaves a working inverter alone, which is often the better call if the existing unit is relatively new.

Worth knowing on cost. The zero rate of VAT on energy saving materials was extended to standalone battery storage on 1 February 2024, so a battery retrofitted on its own to a home with no solar at all still qualifies. That relief runs until 31 March 2027, after which the rate becomes 5 per cent rather than returning to 20.

At commercial scale

Commercial storage is a different calculation. A business with heavy daytime demand may consume nearly everything it generates and need very little storage, while one that runs plant in shifts can shift a great deal of load and justify a large system. The 200kWh installation we completed alongside a 200kW array was sized against the site's real demand profile rather than to match the array.

Larger systems also bring the network operator into the conversation, since anything beyond the small scale thresholds needs a G99 application and may carry an export limit. A capped system still saves exactly the same money on the units it stops you buying, which is usually where the value was anyway.