Batteries and storage

Storage is the most oversold component on a solar quote and one of the most useful, which is an uncomfortable combination. Both halves are true at once.

Useful, because a unit you use is worth roughly six times a unit you export, and a battery is the main way of moving units from one column to the other. MCS’s own guidance shows a typical household going from 23% self-consumption to around 50% with a few kilowatt-hours of storage.

Oversold, because the return flattens steeply and quotes rarely show where. Capacity that does not cycle earns nothing at all, and the size at which cycling stops is lower than most proposals assume — set in November, not July.

So this section is built around arithmetic you can check rather than a recommendation.

We publish no battery prices. Our installed solar costs come from an official statistics series built on MCS installation records. No equivalent series exists for domestic storage that we have found, so every calculation here takes the price from your quote. We would rather leave the number out than invent one.

The things most likely to surprise you

Adding a battery can stop your export payments. If you are on the Feed-in Tariff with metered export, or on the SEG, a battery that can charge from the grid raises the question of whether exported units are eligible at all. Ofgem’s guidance sets out declarations you and your installer must sign — the rules, in plain English.

There is a British standard for where a battery goes, and it rules out more places than you would guess. Bedrooms, escape routes, lofts and windowless cellars among them — PAS 63100 and siting.

The warranty probably ends before the tenth year. Years, cycles and total throughput run at once, and it ends at the first limit reached. The way of using a battery that earns most is the way that gets there soonest — the arithmetic.

LFP is safer, and less decisively than the marketing says. The government’s own review found the lower heat release rate did not have a significant impact at pack level — chemistry, in proportion.

A standalone battery qualifies for zero-rated VAT. No solar required, and it can cycle every night of the year rather than only when there is surplus — the arbitrage arithmetic.