One of the best-documented roofs in Dorking belongs to a co-founder of Dorking Solar Group: a 1930s semi with a 3 kW, twelve-panel array fitted in 2016, which generates about 2,800 kWh of electricity a year. That is a useful number for anyone in RH4 or RH5, but for a battery the annual total is the wrong place to start. What matters is how that output is spread across the year, and in Dorking the spread is wide. Our page on battery storage in Dorking covers where a unit goes and the grid side; this guide is about size.
The model behind the figures below is PVGIS 5.3, the European Commission’s solar tool, run at the Dorking town-centre point for a 4 kWp array facing due south at 35° with 14% losses. It is an estimate for an unshaded roof, not a survey result.
A real roof and the model, side by side
PVGIS puts that 4 kWp array at about 4,049 kWh a year, about 1,012 kWh for every kWp. The Dorking Solar Group semi works out at about 933 kWh per kW of its 3 kW array (our arithmetic). The gap is the kind you would expect between a model of a new, unshaded, due-south array and a real roof fitted in 2016, and it is a reminder that your own figure comes from your own roof. Both numbers agree on the main point: Dorking roofs make plenty of electricity over a year.
Four months that tell the story
Here are the PVGIS monthly figures for Dorking, with daily averages on our arithmetic:
| Month | PVGIS, 4 kWp | About per day |
|---|---|---|
| December | 140 kWh | 4.5 kWh |
| January | 155 kWh | 5.0 kWh |
| June | 495 kWh | 16.5 kWh |
| July | 499 kWh | 16.1 kWh |
December and January together come to about 295 kWh, roughly 7% of the modelled year. June and July come to about 994 kWh, roughly 25% (our arithmetic). December is about 28% of June. That ratio, not the annual total, is what a battery has to live with.
What a Dorking household uses against it
Ofgem’s typical domestic consumption value from 1 July 2026 is 2,500 kWh a year, about 6.8 kWh a day (our arithmetic). Your own bills may show more or less. Either way, the arithmetic for an unshaded south-facing roof runs like this.
In June, the roof makes more than twice the typical day’s use. Some of that is used as it is made; the rest can fill a battery by mid-afternoon, and a battery bigger than your evening use simply tops out and exports the remainder.
In December, the roof makes about 4.5 kWh on an average day, less than the typical day’s use before anything goes into storage. A battery of any size will hold little home-grown electricity. What it can do, if your tariff has a cheaper overnight rate, is charge from the grid at night and cover the evening peak.
So the honest sizing rule is to size for your evenings, not for winter self-sufficiency. Our guide to what size home battery you need walks through reading your own bills to find that evening figure, and the Energy Saving Trust’s view, that a typical home system might be 10 kWh and that there is no exact formula, is the right starting caution.
Box Hill and the things PVGIS cannot see
Dorking sits directly beneath Box Hill in the Surrey Hills National Landscape, and people reasonably ask whether the hills cut their winter output. PVGIS already includes a terrain horizon calculated from elevation data, so the shape of the land around the town-centre point is in the figures above. What it cannot see is trees, a neighbour’s chimney or the house next door, and those bite hardest in December and January, when the sun is low. A roof in Westcott, Westhumble or under the slopes towards Box Hill can lose more in midwinter than the model shows, which pushes the battery further towards evening-shifting from the tariff. We measure shading at the survey for exactly this reason. If cloudy days worry you more than hills, our post on whether solar panels work on cloudy days covers that.
Where Dorking’s housing shifts the answer
Mole Valley is a district of houses with their own walls and garages: 37.6% detached, 28.1% semi-detached, 12.0% terraced and 16.1% purpose-built flats, with 73.2% of households owning their home. In Deepdene, Goodwyns and Chart Downs, a garage or utility room usually has space for a battery of whatever size the evening figure suggests, so space rarely forces the choice. In central Dorking it might. The town-centre conservation area carries an Article 4 Direction on parts of it, and the district has more than 1,000 listed buildings, many on the High Street, West Street and South Street. On a listed house, a smaller unit indoors may be the sensible size simply because it is the one that fits without touching historic fabric.
The network side, briefly
Dorking is in UK Power Networks’ South Eastern Power Networks licence area, about 14.5 km from the nearest SSEN network. A battery counts with any panels towards the 16 A per phase (3.68 kW) G98 line; above it, a G99 application is approved before work starts. A larger battery does not automatically mean a larger inverter, which is what that line measures, so size and paperwork are separate questions. And a standard grid-tied battery shuts down in a power cut unless backup has been designed in, whatever its size.
If you are adding panels too, our page on solar panels in Dorking covers the roof and the Article 4 check, and the Surrey solar panels hub covers schemes across the county.
Sources: PVGIS 5.3, European Commission Joint Research Centre (PVGIS-SARAH3 2005–2023, ERA5, DEM-calculated horizon; monthly run 15 October 2026, annual run 16 September 2026); Dorking Climate Emergency, Walking the Talk; Ofgem, typical domestic consumption values (from 1 July 2026); Energy Saving Trust, Battery storage (updated 19 August 2026); ONS Census 2021, TS044 and TS054, Mole Valley; Mole Valley District Council, Conservation Areas and Listed Buildings; UK Power Networks licence boundaries (December 2024) and NESO GB DNO licence areas (May 2024); Energy Networks Association, EREC G98 Issue 2 (10 March 2025).