SolarSums

How much of your car could your panels charge?

If you drive an electric car, when you plug in matters as much as how far you drive. Charging during a sunny afternoon can use power from your panels that you'd otherwise sell back to the grid for less. Charging overnight uses cheap off-peak power, and charging at other times costs the most. Drag the sliders for how far you drive each week and when you usually plug in, and see where the power comes from and what it costs over a year.

Showing Leeds (LS1 4AP) until you enter a postcode.

Where your charging comes from

Three bars comparing overnight-only, your mix and daytime plug-in. Each bar is split into charging from panels, overnight power and the daytime rate, with annual cost under each.

Each bar splits your car's charging three ways: from your panels, from cheap overnight power, and from the grid at the daytime rate. The figure underneath is what that charging would cost over a year.

From your panels Overnight (Go night rate) Daytime rate

From panels
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Overnight
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Daytime rate
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Total a year
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Car needs
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Rates
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Your driving

0% means you only charge overnight. 100% means the car is plugged in through the day and can take spare solar when there is any.

Your system

Roof faces

Roof pitch is set to 35 degrees, the same as the calculator's default. No battery is modelled here, so spare daytime solar can go to the car first.

How this works

  • Sun data comes from PVGIS, the European Commission's free solar tool, for your postcode, with the same 14% system loss as our calculator.
  • Your panels charge the car only with power the house isn't already using at the time, using the same household split and maths as the calculator.
  • Tariff rates are live Octopus Go rates: the night rate for overnight charging and the day rate at other times. Your own tariff may differ.
  • Solar charging isn't counted as free. Each kWh that goes into the car is one you don't export, so it's costed at the export rate, as in the calculator.
  • Because you choose when the car is plugged in, the planner uses solar for daytime charging whenever that's cheaper than the daytime rate. The calculator assumes the car mostly charges overnight, so its EV figures can differ.
  • The planner assumes a car does 3.5 miles per kWh, the same as the calculator, and allows about 10% for charging losses. Check your own car's figure, as it varies by model and season.
  • Solar can only charge the car while it's parked at home and plugged in, so a car that's out during the day will mostly charge overnight.
  • Nearby postcodes within about 10 km share one set of figures. Shading isn't modelled.

These figures are an illustration to help you understand your options, not financial advice or a quote.

Want payback for panels, a battery and an EV charger together? Open the calculator.