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EV chargingCharging an EV from your own solar
Solar charging feels free, and that feeling is what gets the sums wrong. Every kWh you put in the car is a kWh you did not export, so the decision turns on two numbers you already have. Here is the arithmetic, and what a battery does to it.
Updated 4 August 2026 · written by the Clearline guidance team
The answer, before the reasoning
Charging the car from your own solar is worth doing when your export rate is lower than the rate you would otherwise pay to charge overnight. When your export rate is higher than your off-peak import rate, the better move is to sell the surplus and buy the car's electricity at night. That is the whole decision, and it comes down to two numbers on two bills rather than anything about the charger.
Compare export rate against off-peak import rate
A surplus kWh in the car saves you whatever you would have paid for that kWh later. If you are on a 6.99p overnight EV rate and a 12p export rate, that kWh is worth about 5p more sold than driven. On a 3p or 4p export rate, the same kWh is worth more in the car.
What a kWh of surplus is worth in miles
A 7kW home charger adds roughly 25 to 35 miles of range an hour, which works out at about 3.6 to 5 miles for every kWh that reaches the battery. That is the conversion rate to keep in your head, because surplus solar is measured in kWh and driving is measured in miles, and most disappointment with solar charging comes from never doing that sum.
| Surplus into the car in a day | Miles at 3.6 miles per kWh | Miles at 5 miles per kWh |
|---|---|---|
| 2 kWh | 7 miles | 10 miles |
| 4 kWh | 14 miles | 20 miles |
| 6 kWh | 22 miles | 30 miles |
| 8 kWh | 29 miles | 40 miles |
| 12 kWh | 43 miles | 60 miles |
Derived from a 7kW charger adding roughly 25 to 35 miles of range per hour. Real figures depend on the car, the weather and how it is driven. The left column is surplus, meaning what the roof has spare after the house has taken what it needs, not total generation.
Surplus is the word that does the work there. On a bright day a 4kWp array can be producing well while the fridge, the router and a couple of standby loads absorb a chunk of it, and whatever is left over is all the car ever sees. There is also a hard floor: charging cannot start below about 1.4kW, because the Mode 3 protocol the car and charger use sets a 6A minimum. That is roughly 5 to 7 miles of range an hour at the slowest the car will accept, and it is explained in full in how solar aware EV charging works. If you are still deciding on the array itself, our solar panel guidance covers the sizing side.
The money, worked through
Four realistic combinations, using published rates checked on 3 August 2026. The middle column is what a kWh of surplus is worth in the car compared with exporting it, and the sum is simply the import rate you avoid minus the export rate you give up.
| Your export rate | The import rate you avoid | Value of putting 1 kWh in the car | What that means |
|---|---|---|---|
| 12p, Octopus Outgoing flat | 6.99p, EDF GoElectric Overnight | About 5p worse | Export the surplus, charge the car overnight |
| 12p, Octopus Outgoing flat | 26.11p, no EV tariff, capped average | About 14p better | Charge from solar, then go and get an EV tariff |
| 4p, OVO standard SEG | 8p, Intelligent Octopus Go | About 4p better | Charge from solar wherever you can |
| 3p, British Gas Export SEG | 9p, E.ON Next Drive | About 6p better | Charge from solar wherever you can |
Export rates from the Octopus, OVO and British Gas pages; off-peak rates from the EDF, Octopus and E.ON Next pages; 26.11p is the Ofgem average capped electricity unit rate for 1 July to 30 September 2026. All checked 3 August 2026. Rates vary by region and change often, so re-check before you decide.
The free remote design call runs this comparison on your actual export tariff, your actual off-peak rate and your actual mileage, with no obligation and nobody in your house.
Get your free quote →Why a battery changes the picture
A battery does not just store surplus, it removes the two constraints that make solar charging awkward. The 1.4kW floor is a rule of the conversation between the charge point and the car, so it does not apply to a home battery, which will happily take the small dribble of surplus the car has to refuse. And a battery lets the surplus arrive at a different time from the car, which matters enormously when the car spends the sunniest hours parked somewhere else.
- Self-consumption rises sharply. A solar-only home typically uses around 25 to 30 per cent of what it generates. Add battery storage and that rises to roughly 70 to 85 per cent, which changes what is left to argue over.
- Whole-home off-peak windows work for both. Intelligent Octopus Go, E.ON Next Drive and EDF GoElectric Overnight discount the entire house during the window, so the battery fills at the same cheap rate as the car. EV-only add-ons such as OVO Charge Anytime discount car charging alone, at 14p per kWh on the pay-as-you-go rate.
- Routing solar through the battery is not free. Round trip losses run about 6 to 8 per cent on a DC coupled system and about 8 to 10 per cent on an AC coupled retrofit, so storing a kWh to move it three hours later costs you a slice of it.
- The battery is the better home for small surplus. Below about 1.4kW the car is not an option at all, so on a dull day every spare watt that is not exported has only one place to go.
Decide the pecking order before the kit goes up
A car and a battery left to their own devices will chase the same surplus and cycle each other all afternoon. The fix is an export margin, a setting that holds the charger back until it sees a set level of export, commonly 50W. Which device gets priority is a commissioning decision, and it is far easier to specify up front than to renegotiate later.
Solar in the day, cheap rate at night
The households that get the most out of this stop treating it as a choice. Solar covers daytime charging, weekends and the months when there is genuine surplus; the overnight window covers the commute and the winter, at 6.99p to 9p against a capped average of 26.11p. A decent smart charger moves between the two without anyone touching an app. Our tariff guidance carries the current windows and rates with the date each was checked, and every county page on this site has a local calculator that models the combination for your area, which you can find through the coverage map.
How to work this out for your house
Find your export rate
It is on your export statement or your supplier account. Installer-locked rates of 15p and above and open-market rates of 3p to 4p lead to completely different answers, so use your real number rather than a headline.
Find the off-peak rate you can actually get
Not the cheapest advertised, the cheapest you qualify for. Some rates require a specific charger, a compatible car, a smart meter or an existing account with that supplier.
Subtract one from the other
Off-peak import rate minus export rate. A positive number means solar charging pays. A negative number means export the surplus and charge overnight instead.
Then decide on the charger and the battery
If the sum favours solar, a surplus-tracking charger earns its keep. If it favours the overnight rate, prioritise tariff integration instead, and let the battery handle the daytime surplus.
Not sure which of those four rows you are in? Bring your export statement and your electricity tariff to the design call and we will work it through with you.
Get your free quote →Clearline gives independent guidance and does not install. Installations, including charger siting, CT clamp placement and commissioning, are carried out by an MCS-certified installation team for your area. Tariff rates are regional and change frequently, so confirm the current figures with your supplier before committing.
Solar EV charging questions, answered
Is it cheaper to charge from solar or on a cheap overnight tariff?
It depends entirely on your export rate. If you export at 12p and can charge overnight at 6.99p, every kWh you divert into the car costs you about 5p compared with selling it, so exporting wins. If you are on an open-market export rate of 3p or 4p and an off-peak rate of 8p or 9p, the surplus is worth more in the car by roughly 4p to 6p per kWh. If you have no EV tariff at all and are paying the capped average of 26.11p, solar charging wins comfortably, but the bigger saving is getting onto an EV tariff.
How many miles will a day of solar surplus actually give me?
Around 3.6 to 5 miles per kWh of surplus, derived from a 7kW charger adding roughly 25 to 35 miles of range an hour. So 4 kWh of surplus is about 14 to 20 miles and 8 kWh is about 29 to 40 miles. Surplus means what is left after the house has taken what it needs, which on many days is a good deal less than total generation.
Can I charge my car from solar alone?
Yes, using a surplus-only mode such as the Zappi's ECO+ or the Hypervolt Home 3 Pro's Super Eco, which pause charging when the house is importing and resume only when there is spare generation. The limit is that nothing happens below about 1.4kW of surplus, because the Mode 3 charging protocol sets a 6A minimum. That makes solar-only charging practical for a car that sits on the drive during the day and frustrating for one that commutes.
Does a home battery make solar EV charging better?
It makes the whole system work harder rather than making the car charge faster. A battery captures the small surplus the car cannot accept, lifts self-consumption from roughly 25 to 30 per cent up to roughly 70 to 85 per cent, and lets daytime generation reach the car in the evening when it is actually parked. The cost is a round trip loss of about 6 to 8 per cent on a DC coupled system or 8 to 10 per cent on an AC coupled retrofit.
Will my battery and my EV charger fight over the same surplus?
They will if nobody sets a priority order. Both watch the same meter reading, so the battery starts charging, the export disappears, the car backs off, the battery fills, the export returns and the cycle repeats. An export margin setting, which delays the charger until it sees a set level of export such as 50W, stops the two chasing the same watt.
Do I need a special charger to charge from solar?
You need one that can read your import and export, which means a CT clamp fitted on the incoming mains. The myenergi Zappi ships with a clip-on grid sensor and offers ECO, ECO+ and FAST modes with charge current variable from 6A to 32A; the Hypervolt Home 3 Pro includes its solar CT clamp in the box and offers Boost, Eco and Super Eco. Ohme markets solar charging as Solar Boost through its own CT and app. A plain timer charger cannot do any of this.
Should I size the array differently if I am charging a car?
Usually yes, because an EV is the largest single load most homes will ever add and it turns surplus that would have been exported cheaply into miles. The fixed costs of an installation, the scaffold, the crew day and the network application, do not change with array size, so extra panels are the cheap part. Our EV charging guidance and the county calculators model the combination together.
See the numbers next: Duracell Dura16, installed, or what a battery costs.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- 7kW home charger range added per hour, used to derive miles per kWh proev.co.uk
- myenergi support forum, the 1.4kW Mode 3 minimum charge rate and the export margin setting myenergi.info
- myenergi Zappi v2.1 datasheet, ECO, ECO+ and FAST modes, 6A to 32A variable current, supplied clip-on grid sensor myenergi.com
- Hypervolt Home 3 Pro solar modes, Boost, Eco and Super Eco, and included solar CT clamp bestchargers.co.uk
- Octopus Outgoing flat export rate and Intelligent Octopus Go off-peak rate and window octopus.energy
- EDF GoElectric Overnight off-peak rate and window edfenergy.com
- E.ON Next Drive off-peak rate and window eonnext.com
- OVO standard SEG export rate and Charge Anytime pay-as-you-go rate ovoenergy.com
- British Gas Export SEG open-market export rate britishgas.co.uk
- Ofgem average capped electricity unit rate, 1 July to 30 September 2026 ofgem.gov.uk
- Household self-consumption with and without battery storage solarthermuk.co.uk
- AC coupled and DC coupled round trip efficiency losses greenreachenergy.co.uk
Read next
How solar aware EV charging actually works
The CT clamp, the surplus tracking and the 1.4kW floor that catches people out.
Read the guide →How time of use charging windows actually work
How a cheap overnight window is metered and billed, and what a battery does inside it.
Read the guide →Adding a battery to solar panels you already own
Retrofitting a battery to working solar is straightforward. The paperwork is where people trip up.
Read the guide →