Three seasons of surplus
Using PVGIS monthly output for central Liverpool (PVGIS 5.3) and Ofgem's typical household use of 2,500 kWh a year, about 6.8 kWh a day (Ofgem), here is an average day for a 3.5 kW system on a 35° roof:
| Season | South roof | West roof | East roof | Typical use |
|---|---|---|---|---|
| Winter (Nov–Feb) | 4.4 | 2.2 | 2.2 | 6.8 |
| Spring and autumn (Mar, Apr, Sep, Oct) | 9.9 | 7.4 | 7.4 | 6.8 |
| Summer (May–Aug) | 13.4 | 12.4 | 11.9 | 6.8 |
In summer the panels make well over the day's use, much of it around midday; that is what a battery holds for the evening. In winter they make a fraction of it, so almost everything is used as it is produced. Some households give a battery a winter role by charging it overnight on a cheaper tariff, which only makes sense on your own supplier's rates.
A west roof does some of the shifting
In Liverpool a west roof at 35° makes about 766 kWh a year per kW against 749 for east (PVGIS), and its output peaks in the afternoon, closer to when a working household starts using power. If your best slope faces west, you may need a smaller battery, or none, to use most of what you make. The estimator compares directions.
Choosing a size
Size a battery to two numbers: the surplus on a good day and your use between sunset and bedtime. A smart meter's half-hourly data shows the second. On a terrace with room for 2 to 3 kW of panels the summer surplus is modest, and a large battery would often sit half empty; beyond what you can fill and empty most days, extra capacity adds cost and little else.
Batteries and the council's grant
Liverpool City Council's Warm Homes: Local Grant lists batteries among its measures alongside solar panels, for homes at EPC D to G where the household qualifies through an income below £36,000, a means-tested benefit or a qualifying postcode (Liverpool City Council). The council says the scheme is oversubscribed for its second year, 1 April 2026 to 31 March 2027, and that registering now counts towards year three from 1 April 2027. If a battery comes through the grant, its size will follow the scheme's assessment of the home rather than a sales conversation. For everyone else, a battery is paid for privately; see paying for solar.
Two months mark out the range for a 3.5 kW south-facing system in the city centre. In July an average day leaves about 6.5 kWh beyond a typical household's use; in December the same roof falls about 3.7 kWh short (our arithmetic from PVGIS 5.3 and Ofgem). A battery sized near the July figure fills on most summer days and is close to idle in midwinter unless it is charged from the grid overnight, which turns on your tariff rather than your roof. The costs page has the panels' side of a combined quote.
Tenure matters here too. With 26.1% of households renting privately and most social tenants renting from housing associations (Census 2021), a battery in a rented home is the landlord's decision, as are the panels it would store power from. For an owner weighing one up, the questions on the installer page apply to the battery line of the quote as much as the panels.
What batteries cost
DESNZ publishes median installed prices for batteries added to existing homes (DESNZ):
| Capacity | Per kWh | Example |
|---|---|---|
| Under 6 kWh | £1,300 | 5 kWh: about £6,500 |
| 6 to 11 kWh | £890 | 9 kWh: about £8,000 |
| 11 to 30 kWh | £630 | 13 kWh: about £8,200 |
Bigger batteries cost less per kWh, so the bands are a guide. Installed batteries are zero-rated for VAT until 31 March 2027, then 5% (HMRC). Fitting one with the panels saves a second scaffold; see what solar costs.
For qualifying households, Liverpool City Council's Warm Homes: Local Grant lists PV batteries among its measures: homes at EPC D to G with a qualifying postcode, a means-tested benefit or income under £36,000. It is oversubscribed for year two (Liverpool City Council); see help with the cost.
SP Energy Networks and storage
SP Energy Networks runs Liverpool's network. For a single generator under 16 amps per phase (3.68 kW), it must be told before or at commissioning, and the commissioning confirmation sent within 30 days (SP Energy Networks). A battery inverter counts alongside the solar inverter, so solar plus a battery can exceed the limit; above it, the installer applies and waits for agreement, or designs the system with export limiting that the network accepts. The grid connection guide has the detail.
Where it can go
The British Standards Institution's PAS 63100 sets out where home batteries may be installed, keeping them away from escape routes and sleeping areas, and an MCS installer should follow it (BSI). In a Liverpool terrace the narrow hall is often the only way out, so the usual answers are a weatherproof enclosure in the rear yard, an outbuilding, or a utility space off the escape route. Ask the installer to show the spot and explain why it meets the guidance.