About 487 kWh in June. About 135 kWh in December. Those are PVGIS 5.3’s estimates for a 4 kWp array facing due south at 35° in Cobham, and the gap between them is the most useful thing to understand before anyone sizes a battery for your house. A battery that looks right against a June afternoon can look very different against a December one, and the honest size sits between the two.
This guide works through both months with the town’s own figures and sets out what they mean for capacity. For where a battery goes in a Cobham home and how it connects, see our page on battery storage in Cobham.
The two months side by side
PVGIS, the European Commission’s solar tool, gives about 3,990 kWh a year for that 4 kWp array in Cobham, using the satellite record for 2005 to 2023. June brings about 487 kWh and July about 491 kWh; December about 135 kWh and January about 154 kWh. Divided across each month, that is roughly 16.2 kWh a day in June and 4.4 kWh a day in December, so a December day yields about 28% of a June day (our arithmetic, for an unshaded roof).
The sunshine record agrees on the shape. The Met Office station at Wisley, about three miles from Cobham, averaged 1,584 hours of sunshine a year over 1991–2020, with around 208 hours in July and around 47 in December. Panels generate from daylight rather than direct sun alone, which is why the December output is not as low as the sunshine hours suggest, but the winter dip is real. Our guide to whether solar panels work on cloudy days explains the difference.
Set against what a Cobham home uses
Ofgem’s typical domestic consumption value from 1 July 2026 is 2,500 kWh a year for a medium, single-rate home, about 6.8 kWh a day (our arithmetic). Your own figure may be well above that: a larger detached house on Fairmile or in Stoke D’Abernon, an electric car or electric heating all push it up. But the comparison holds at any size. In June, the 4 kWp roof makes more than twice the typical day’s use. In December, it makes less than the typical day’s use, even before the timing problem that most electricity is used outside daylight.
June: more to store than you can use
On an average June day in Cobham, the array produces about 16.2 kWh. A household out at work might use only a few kWh while the sun is up, leaving the rest to export or store. On paper, that fills a 10 kWh battery with room to spare. Real June days vary with cloud, and any Cobham roof under mature trees can lose real output to shade, so the paper figure is a ceiling rather than a promise.
December: little left over
On an average December day, the same roof makes about 4.4 kWh, and the house uses most or all of it as it is generated. A battery sized to catch June’s surplus will often go into a December evening nearly empty. That is not a fault; it is the season, and it is the same on every unshaded south-facing roof in KT11.
Size for the evening, not for winter
The practical rule follows from the two months. Size a battery to what your house uses between sunset and bedtime, and to what the array can spare on a typical spring or summer day, not to winter self-sufficiency, which no battery delivers on a Cobham roof. The Energy Saving Trust says there is no exact formula, puts a typical home system at 10 kWh and a 5 kWh system at around £4,600, with a typical lifespan of about 10 to 12 years. Our guide on what size home battery you need shows how to read your own bills for the evening figure.
In winter, a battery can still earn its place a different way: charging on a cheaper overnight rate and covering the dearer evening hours, the same way a battery works without panels. Whether that adds up depends on the gap between your tariff’s rates, not on the roof.
What Cobham’s housing changes
In Cobham and Downside ward, 30.9% of households live in detached houses and 27.6% in semis (Census 2021), so plenty of local roofs can take more than 4 kWp. A larger array scales both months, but not equally in absolute terms: doubling to 8 kWp takes June from about 487 kWh to about 974 kWh, while December only goes from about 135 kWh to about 270 kWh (our arithmetic on the PVGIS figures). More panels add a lot of summer surplus and a little winter help. That is a case for a sensibly sized battery, not an oversized one.
The network side
Cobham’s town centre sits in UK Power Networks’ South Eastern Power Networks licence area. A larger array or a bigger battery inverter often takes a system past 16 A per phase (3.68 kW), which means a G99 application approved before work starts rather than a G98 notification; the installer handles it. We are a NAPIT member (73495), MCS-certified for solar PV and battery storage through NAPIT. The roof side is on our page for solar panels in Cobham, and the county picture on our Surrey solar page.
Sources: European Commission JRC, PVGIS 5.3, PVGIS-SARAH3 2005–2023, 4 kWp, 35°, due south, 14% losses (run 15 October 2026); Met Office, Wisley 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 (Cobham and Downside ward); UK Power Networks and NESO licence boundary data; Energy Networks Association, EREC G98 Issue 2 (10 March 2025). Read 12–15 October 2026.