Panels and an electric car look like a perfect match on paper, and in Staines-upon-Thames they are, for about half the year. The other half, the roof makes too little to spare. The way to see where the line falls is to take the month-by-month output for a Staines roof and set it against what a house uses. This post does that, in our own arithmetic on published figures. For the charger itself, the fuse check and the network boundary, see our page on EV charging at home in Staines-upon-Thames.
We ran PVGIS 5.3, the European Commission’s solar calculator, on 19 October 2026 at the Staines town-centre point, for a 4 kWp array facing due south at 35°, with 14% system losses. The year comes out at about 3,995 kWh.
The PVGIS year for a Staines roof
The middle column is PVGIS’s monthly output for the Staines town-centre point. The third divides it by the days in the month. The fourth subtracts 6.8 kWh, a typical household’s daily use on Ofgem’s 2,500 kWh a year, to show what would be left if the house took a full day’s use from the roof. The last two columns are our arithmetic.
| Month | PVGIS kWh | kWh a day | Left after 6.8 kWh |
|---|---|---|---|
| January | 158 | 5.1 | none |
| February | 207 | 7.4 | 0.5 |
| March | 337 | 10.9 | 4.0 |
| April | 444 | 14.8 | 8.0 |
| May | 477 | 15.4 | 8.5 |
| June | 482 | 16.1 | 9.2 |
| July | 487 | 15.7 | 8.9 |
| August | 438 | 14.1 | 7.3 |
| September | 374 | 12.5 | 5.6 |
| October | 271 | 8.7 | 1.9 |
| November | 184 | 6.1 | none |
| December | 138 | 4.5 | none |
The subtraction is deliberately cautious. Some of a Staines house’s use falls at night, when the roof makes nothing, so the daytime surplus on a sunny day can be larger than the last column shows. Cloudy weeks make it smaller. These are averages for an unshaded south-facing roof, not a survey result.
Summer: what the surplus can add
From April to September, the table shows a Staines roof making roughly 5.6 to 9.2 kWh a day more than the house uses. Over those six months, our arithmetic puts that at about 1,450 kWh above the typical household’s use. Our EV page uses a 60 kWh car battery as its worked example, so on paper that is the energy for roughly two dozen full charges over a summer. In practice the car only takes what arrives while it is plugged in, so a household with someone at home in the day, or a second car that sits on the drive, gets the most from it.
Rate matters as well as quantity. A 4 kWp array on a Knowle Green semi never reaches 7 kW, and around midday on a good June day the house takes its share before the car. Solar charging is a slow, steady top-up, not a fast fill.
Spring and autumn: the shoulder months
In Staines, March and October sit in between, at about 4.0 and 1.9 kWh a day left over after the house. A sunny weekend in either can still put useful energy into a car that stays at home; a dull week puts in almost none. These are the months when a charger that follows solar output, rather than a fixed timer, earns its keep.
Winter: the grid does the work
From November to January a Staines roof makes less than the typical house uses: about 4.5 kWh a day in December against 6.8. Whatever the panels make, the house uses, and the car charges from the grid. On our arithmetic, October to March together produce about 1,295 kWh, roughly a third of the year. That is why the overnight tariff matters more than the roof from November to February. Every new home chargepoint sold in Great Britain has had to be smart since 30 June 2022, so the charger can run in the cheapest hours without you setting an alarm.
What has to be true in a Staines home
For a Staines household, three things have to be true. The car has to be at home and plugged in while the sun is up. The charger needs a compatible set-up that can follow solar surplus, which the survey checks against your panels and inverter. And the roof has to be yours and reasonably clear of shade. The home EV charger installation page explains the SmartBee-M we fit and what a compatible solar set-up involves.
Which Staines homes this applies to
In the Staines and Staines South wards, 35.0% of households live in semis, 21.2% in terraces, 9.0% in detached houses and 29.1% in purpose-built flats (2021 Census). The table applies to the houses with their own roofs: a semi off Laleham Road or in Knowle Green with a south or near-south slope comes closest to it, and an east-west roof makes less. For flats the shared roof belongs to the freeholder. If you are weighing up panels, solar panels in Staines-upon-Thames covers the roof side; if you are thinking about a battery too, where a home battery goes in a Staines home covers siting.
The centre of Staines sits in SSEN Distribution’s Southern Electric Power Distribution area, about 1.7 km from UK Power Networks’ South Eastern area. Whichever serves your postcode, the installer notifies it of the charger and, for the panels, follows G98 or G99, a 4 kW inverter being just over the 3.68 kW G98 line.
Sources: European Commission Joint Research Centre, PVGIS 5.3, PVGIS-SARAH3 2005–2023, 4 kWp, 35°, due south, 14% losses, building-mounted, Staines-upon-Thames town-centre point (51.4338, −0.5118), run 19 October 2026; Ofgem, Typical Domestic Consumption Values from 1 July 2026; Electric Vehicles (Smart Charge Points) Regulations 2021 (S.I. 2021/1467); ONS Census 2021, TS044, Staines (E05007370) and Staines South (E05007371) wards, via Nomis; NESO, GIS boundaries for GB DNO licence areas (May 2024); SSEN Distribution, Who we are; Energy Networks Association, EREC G98 Issue 2 (10 March 2025).