Ask what a home battery does across a Finchley year and the honest answer comes in two halves. In June a south-facing roof in N3 or N12 makes far more electricity than most homes use in daylight, and the battery’s job is to carry that surplus into the evening. In December the same roof makes so little that there is often nothing spare to store at all. This guide puts numbers on both halves using PVGIS runs for Finchley, and explains why the sensible size for a battery here is set by your evenings rather than by either month. For how we approach storage on Finchley homes, see our page on home battery storage in Finchley.
The figures come from PVGIS 5.3, the European Commission’s solar model, run for a point in Finchley with the settings we use across the site: 4 kWp of panels facing due south at 35°, 14% system losses, on the 2005–2023 PVGIS-SARAH3 satellite record. On those settings Finchley comes out at about 3,952 kWh a year, the same annual figure shown on our solar panels in Finchley page. That is the best case for an unshaded roof; an east or west slope, or the shadow of a neighbouring gable on a Woodside Park side street, pulls it down.
June: a surplus to carry into the evening
PVGIS puts the Finchley array at about 476 kWh in June and 479 kWh in July. Across June’s 30 days that is roughly 15.9 kWh a day. For scale, Ofgem’s typical domestic consumption value from 1 July 2026 is 2,500 kWh a year, which averages about 6.8 kWh a day. On those two averages, a Finchley house with the whole 4 kWp roof to itself generates roughly 9 kWh a day more than it uses in June (all our arithmetic). The Met Office station at Hampstead, the nearest to Finchley with a sunshine record, averaged about 194 hours of sunshine in June and about 200 in July over 1991–2020.
Not all of that 9 kWh reaches a battery. Some of what the house uses falls in daylight anyway, and if someone is home during the day the kettle and the washing machine take their share as the power is made. What is left after that is the surplus a battery can hold for after sunset. Without one, it is exported.
December: little or nothing to store
The same Finchley array makes about 142 kWh in December and 158 kWh in January, according to PVGIS. December’s figure is about 30% of June’s, and January’s about 33% of July’s. Per day, December works out at roughly 4.6 kWh, below the 6.8 kWh a day of average use (our arithmetic again). Hampstead’s December sunshine average is about 54 hours, against about 194 in June.
In practice, a Finchley household in December will usually use what the roof makes as it is made, and a solar-charged battery will often start the evening close to empty. No battery, however large, changes how little a north London roof produces in the shortest month.
Why the battery is sized to the evening
Put the two months side by side and the sizing logic follows. A battery big enough to soak up every June surplus from a Finchley roof would sit part-empty for much of the winter, and no size fixes December. The useful question is how much electricity your household uses between the panels going quiet and bedtime, and how much of that a typical spring, summer or early-autumn day’s surplus can cover.
The Energy Saving Trust says there is no exact formula for working this out. It describes a typical home system as perhaps 10 kWh, puts a 5 kWh system at around £4,600 and says a battery’s typical lifespan is about 10 to 12 years. Our guide to what size home battery you need walks through reading your own bills for the evening figure. PVGIS cannot see your shading or your habits, so treat the Finchley numbers as a guide, not a forecast for your roof.
What Finchley’s housing does to the numbers
Many Finchley homes do not have a whole 4 kWp roof to themselves. In Finchley Church End ward, 40.4% of households live in purpose-built flats and 16.4% in converted-house flats, and West Finchley has the highest converted share of the four wards at 17.7% (Census 2021). Where a roof is shared between flats, each household’s share of the array is smaller, and the June surplus and December trickle shrink with it. A battery sized for a full roof on a share of one would repeat the June mistake in a smaller form. Hendon’s even more flat-heavy streets raise the same question from another direction, covered in our guide to where a home battery goes in Hendon.
Planning can trim the array too. Barnet’s records list the solar class among the permitted-development rights removed by the Finchley Garden Village and Moss Hall Crescent Article 4 directions, so on those streets the number and position of panels is checked before anyone suggests a battery size.
Winter, tariffs and charging from the grid
Because a Finchley roof makes so little in December, some households look at charging a battery overnight on a time-of-use tariff and using it in the evening peak. That only pays where the gap between the cheap and standard rates is wide enough, and our guide to battery storage without solar panels sets out that arithmetic honestly. One more winter point: a standard grid-tied battery shuts down in a power cut unless the system is designed with backup, so dark December evenings are not, on their own, a reason to buy one.
Getting a figure for your own Finchley roof
Everything above is modelled for an unshaded due-south roof in Finchley. Your own figures depend on direction, pitch, shade and when your household uses power, which is what a survey measures. Residential battery installations carry 0% VAT until 31 March 2027 and 5% from 1 April 2027. Our solar panels in North London hub covers the wider area; across Finchley, Hendon, Edgware and Harrow our PVGIS runs sit within about 30 kWh a year of one another, so your roof matters far more than your postcode. If a battery would not earn its place on your Finchley home, we will say so. You can ask for a survey through our contact page.
Sources: PVGIS 5.3, European Commission Joint Research Centre (PVGIS-SARAH3 2005–2023; 4 kWp, 35°, due south, 14% losses; Finchley monthly and annual runs, 15 October 2026); Met Office, Hampstead location-specific long-term averages 1991–2020; Ofgem, typical domestic consumption values from 1 July 2026; Energy Saving Trust, Battery storage (updated 19 August 2026); ONS Census 2021, TS044 accommodation type, Finchley Church End and West Finchley wards, via Nomis; planning.data.gov.uk, article-4-direction-area dataset, London Borough of Barnet; HMRC, VAT Notice 708/6. Daily and percentage figures are our arithmetic on the PVGIS and Ofgem figures.