A battery with your panels: does it add up in St Helens?

How much there is to store

PVGIS 5.3 monthly output for central St Helens, south at 35°, 14% losses. Surplus assumes Ofgem's typical 2,500 kWh a year, with a third of each day's use falling in daylight; real households vary widely. Read 3 November 2026.

From spring to early autumn, a household out during the day has several kilowatt-hours a day the panels make but the house does not use. That is what a battery can hold for the evening. From November to January the panels rarely make more than the house uses, so the battery mostly sits idle unless it is charged from a cheap night tariff.

The value of a stored unit

Storing a unit instead of exporting it is worth the difference between your unit rate (26.32p per kWh on average under Ofgem's cap for October to December 2026) and your export rate, minus a little lost in charging. On a small system that difference applies to fewer units, which is why batteries tend to make most sense on larger systems or in households that use most of their power after dark.

A worked year for a 5 kWh battery

Suppose a 5 kWh battery took each day's average surplus from the table above, up to its capacity, and the house used all of it in the evening. Over a year it would hold about 1,433 kWh. Bought at 26.32p instead of exported at 5p, that is worth about £305, before the few per cent lost in charging and discharging. Real days swing above and below the average, and a household that is home all day has less surplus to store, so treat this as an upper guide for this system rather than a forecast.

The dark months

From November to January the average day's output from this system is between 3.1 and 4.4 kWh, and on the page's assumptions it leaves 0.8 kWh to spare on an average December day. A battery charged only by the panels therefore does little in winter. Some households also charge one overnight on a cheaper tariff and use that at the evening peak; that is a tariff decision, separate from the solar sums.

Sizing

• Look at what you use between late afternoon and morning; that sets the useful size, often a few kWh for a small household.
• Do not buy capacity the panels cannot fill: on a 3.5 kW system, a very large battery will rarely be full.
• Ask whether the system can keep some circuits running in a power cut; many cannot without extra equipment.

Paying for one

Batteries installed in homes are zero-rated for VAT until 31 March 2027, with or without new panels. The Warm Homes Loan Scheme has its own £15,000 cap for an electrical storage battery. For lower-income households in homes rated D to G, national Warm Homes: Local Grant guidance lists domestic batteries as an eligible measure alongside solar; check with the scheme.

A battery and the connection

Storage can change how the system is connected. A battery that shares a hybrid inverter adds nothing to what could be exported. A battery with its own inverter adds that rating to the solar inverter's, so a 3.6 kW solar inverter alongside a 3 kW battery inverter needs approval from the network operator before switch-on rather than a notification afterwards. Adding a battery to existing panels raises the same question; see network connection.

Questions to put to the installer

• How much of the battery's capacity can actually be used, and how fast can it charge and discharge?
• Hybrid or separate inverter, and what does that mean for the connection?
• Will it charge from the grid overnight, and does the export tariff pay for anything it sends out?
• What warranty covers it, in years and in cycles?

Batteries are not in the government's per-kW averages, so price one as its own line rather than against prices, and test its value against the first-year sums on worth it.

Where it goes

A battery and its inverter need a dry, ventilated spot, often a garage, utility room or an outside wall. Small terraced houses may have little spare space indoors, so ask early where the installer would put it and how the cables would run. The installer must include the battery in what it tells SP Energy Networks; see network connection.

Related pages

• First-year sums
• Network connection
• Grants and loans
• Prices

References

1. PVGIS 5.3 photovoltaic estimates (EU Joint Research Centre)
2. Ofgem (May 2026): typical domestic consumption values
3. Ofgem: the energy price cap, unit rates by region
4. Ofgem: how export payments work for small generators
5. SP Energy Networks: generation connections
6. Department for Energy Security and Net Zero: solar PV cost data (2025/26)
7. Warm Homes Loan Scheme rules, version 3 (September 2026)
8. Warm Homes: Local Grant policy guidance, DESNZ (updated June 2026)
9. St Helens Borough Council: sustainable warmth and the Warm Homes: Local Grant
10. HMRC Notice 708/6: zero rate for installing solar and batteries in homes