Charging an electric car from solar panels: diverters, batteries and the export rate

A solar aware charger can fill the car with power your panels would otherwise export. Whether that saves money depends on two numbers most people never compare: what you are paid to export a unit, and what you would pay to buy it at night.

In an Energy Saving Trust case study, a household with a 4.2kW solar system and an electric car used only 40% of what the panels generated, in the house or in the car. The rest went to the grid. That gap is what a solar aware charger tries to close, and it is worth knowing how small or large it is in your house before paying for one.

How a charger follows the sun

A solar aware charger, or a separate solar diverter, measures how much electricity is leaving the house through the meter. When the panels make more than the house is using, it sends that surplus to the car instead of letting it be exported. As a cloud passes or the kettle goes on, the charging rate falls. Some also have a mixed mode that tops up from the grid to keep the car charging.

The car needs to be at home and plugged in while the sun is up. MCS, the certification body for small renewables, says in its solar PV standard that full self use is unlikely in most homes "because the EV is not home or plugged in". A car that leaves for work at eight and comes back at six will catch little of a weekday's output.

The smart charger regulations do not get in the way. The product safety regulator, OPSS, which enforces them, states that for now it will not act over the randomised start delay when a charger is following power generated on site, such as solar (OPSS guide, paragraph 3.43).

The comparison that decides it

Every unit of solar that goes into the car is a unit you do not export. So the value of charging from solar is what you would have paid for that unit, minus what you would have been paid to export it.

The Energy Saving Trust says export payments under the Smart Export Guarantee are typically around 12p a unit. Each supplier sets its own rate, and Ofgem requires only that it is above zero.

Take 10kWh of surplus on a sunny day, sent either to the grid or to the car.

Your import tariff	Value of 10kWh in the car	Paid for exporting 10kWh at 12p	Better choice
Cap rate, 26.32p	£2.63	£1.20	Charge the car
EV tariff with a 7p overnight rate	£0.70	£1.20	Export, charge at night

The cap rate is Ofgem's average Direct Debit rate for the quarter. Which? quotes 7p as an overnight EV rate in its guide to charging costs. Both are examples; put your own tariff and export rate into the same sum.

This is the drawback nobody selling solar charging leads with. A household already on a cheap overnight EV tariff can earn more by exporting its daytime surplus and charging the car at night. Solar charging pays best for cars that are home in the day and households without a cheap night rate. It also suits anyone who wants the car charged from their own panels for its own sake, which is a fair reason, but a different one from saving money.

Summer and winter

The Energy Saving Trust's case study is direct about the dark months: "you'll still need to use electricity to charge your EV during the winter months." Orientation matters too. Its solar advice, updated August 2026, says an east or west facing roof gets around 15 to 20% less energy than one facing south, and puts the average system at around 4.5kWp, costing around £7,600.

Where a battery fits

A home battery stores daytime surplus for the evening, which can include charging a car that comes home after dark. The Energy Saving Trust says battery systems typically cost £5,000 to £8,000. Compare the battery's usable capacity with the car's before assuming it can refill the car each evening, and ask the installer to size it against what the house itself uses after dark.

Cars that power the house or export to the grid, known as vehicle to home and vehicle to grid, are still at the policy stage. The government's Clean Flexibility Roadmap, updated July 2026, expects bidirectional charging to matter "over the coming years" and promises a consultation on chargepoint standards by the end of 2026.

VAT and the network operator

Item	VAT until 31 March 2027	Source
Solar panels, installed	0%	HMRC Notice 708/6
Battery, installed, including a standalone one	0%	Same notice, since 1 February 2024
Smart diverter, installed	0%	Same notice, since 1 February 2024
EV charger	Not on the list	Same notice

From 1 April 2027 the listed items return to 5%. The relief applies only when the item is installed, not bought on its own.

Adding panels or a battery also involves the network operator. Systems under 16A per phase, about 3.68kW, are fitted and then notified within 28 days under a process called G98, says National Grid. Larger ones need an application under G99 first. The ENA counts solar and battery storage together for that threshold, so a battery added to an existing solar system can tip it into an application. The charger has its own notification, covered in our fuse board and DNO guide.

Installers who fit chargers alongside panels and batteries are listed under solar and battery EV charging, and the quote form asks if you already have panels or a battery.