Adding a battery to solar panels on the Wirral

How much spare power a Wirral roof makes

The table compares what a 4 kW south-facing system on the Birkenhead side makes each day, on average, with what a home using Ofgem's typical 2,500 kWh a year uses each day (about 6.8 kWh). In summer the panels make two or three times a day's use; in midwinter they make about half.

Output: PVGIS 5.3, south at 35°, 14% losses, Birkenhead side. Use: Ofgem's typical domestic consumption value (2,500 kWh a year) spread evenly; real homes use more in winter. Checked 3 November 2026.

Two conclusions follow. From April to September a Wirral roof makes far more than a home uses by day, and without a battery much of that goes to the grid at the export rate. From November to January the panels make less than the home uses, so there is little or nothing to store; a battery then earns its keep only if you charge it overnight on a cheaper tariff.

What a battery changes

Every unit you use yourself saves you the import price, 26.32p per kWh on average under Ofgem's cap for October to December 2026. Every unit you export earns the export rate, around 12 to 13p at best under the Smart Export Guarantee and much less on some tariffs. A battery moves units from the second column to the first. In our year-one sums it lifts the share of a 4 kW system's output used at home from about a third to about half or more, which is where most of its value lies.

A battery can also charge from the grid at night on a time-of-use tariff and run the house in the expensive evening hours. On the Wirral that use matters most in winter, exactly when the panels have little to give, so the two jobs fit together across the year.

Choosing a size

• Size to your evening and overnight use. Look at your smart meter data or app for what you use between about 4pm and 8am. That, not the size of the panels, is what a battery can cover.
• Usable, not nominal, capacity. Compare batteries on the energy you can actually use, which is a little less than the headline figure.
• Power, not just capacity. A battery's power rating limits how fast it can supply the house: a kettle and an oven together need more than a small battery can give.
• Room to grow. If an electric car or heat pump is likely, ask whether the battery can be extended later.

One inverter or two

If you are fitting panels now and might add a battery later, a hybrid inverter that can run both avoids buying a second inverter and keeps the system's total export within one rating, which can keep it under the simpler G98 connection process. A battery added later with its own inverter may need a G99 application to SP Energy Networks first. See connecting to the grid.

Where it goes, especially near the sea

Batteries last longest somewhere dry, ventilated and not too hot or cold: a garage, utility room or a suitable cupboard. On the open coast from New Brighton to West Kirby, keep the battery and its inverter indoors unless the product is specifically rated for outdoor coastal use. Ask the installer where they propose to put it and why, and check the manufacturer's installation rules. Batteries are covered by their own MCS standard, separate from the one for solar panels.

Tax, grants and paperwork

• VAT: batteries installed in homes, with panels or on their own, are zero-rated until 31 March 2027, then 5%.
• Grants: the Warm Homes: Local Grant, run in Wirral by the Combined Authority, lists batteries alongside solar panels as measures it can fund for eligible households. There is no grant for batteries for everyone.
• Paperwork: keep the battery's warranty, which usually states a number of years and a minimum remaining capacity, with your other system documents.

Power in a cut

Most battery systems stop supplying the house during a power cut unless they have a backup or emergency power function and the wiring to match. If keeping the lights on in a cut matters to you, ask specifically which circuits would stay live and for how long.

Our view

For many Wirral households the sensible order is: panels first, with a battery-ready inverter; a smart meter and the best export tariff you can get; then a battery once you have seen a year of your own generation and use. If you are home little in the day and the evening is when you use most, adding the battery at the same time can make sense. Either way, compare quotes on usable capacity, power, warranty and where it will be installed.