Solar & EV Charging: How to Use Your Panels to Charge for Free
If you have solar panels, you can charge your EV from surplus generation — potentially for zero cost. Here's how it works and what you need.
How Solar EV Charging Works
A solar panel system generates electricity during daylight hours. When generation exceeds your household demand, the surplus is either exported to the grid (at the export tariff rate, typically 4–15p/kWh) or diverted to useful loads — like your EV.
A solar-compatible EV charger monitors the surplus generation in real time and adjusts its charging rate to match. Rather than drawing from the grid, the charger uses the free surplus electricity. This is called solar diversion or solar surplus charging.
Grid electricity costs 25–28p/kWh. Export tariffs pay 4–15p/kWh for surplus. Using that surplus to charge your EV at ~4 miles per kWh saves 25–28p per kWh — far more than you'd earn by exporting it.
What You Need for Solar EV Charging
| Component | Purpose | Required? |
|---|---|---|
| Solar PV system | Generates the electricity | Yes |
| Solar-compatible EV charger | Adjusts charge rate based on surplus | Yes — must support solar diversion |
| CT clamp (current transformer) | Measures household import/export in real time | Yes — on most systems |
| Solar inverter with export data | Some chargers read generation data from the inverter directly | Depends on charger |
| Battery storage | Stores daytime surplus for evening/overnight use | Optional — increases self-consumption |
Solar Charging Modes Explained
Most solar-compatible chargers offer several modes:
- Pure solar / ECO+ mode: Only charges when there's sufficient solar surplus. Charging pauses when surplus drops and resumes when it recovers. Maximises free solar use but charging is intermittent.
- Solar boost mode: Charges from solar surplus plus a configurable top-up from the grid. Ensures a minimum charge level even when solar is insufficient.
- Off-peak + solar combination: Charges from solar during the day, tops up from the grid during the cheap overnight window. Best of both worlds.
EV charging requires a minimum of 6A (~1.4kW). Solar diversion only works when surplus generation exceeds this threshold. On cloudy UK days, this can mean limited solar charging. Pairing solar diversion with an overnight off-peak tariff gives the best result year-round.
Frequently Asked Questions
Do I need a specific EV charger for solar diversion?
Yes — not all chargers support solar diversion. You need a charger that can vary its output between 6A and 32A (rather than simply on/off), and which can read CT clamp data or inverter generation data. Examples include the myenergi Zappi, certain Hypervolt models, and selected other brands. Check compatibility before purchase.
How much can I save with solar EV charging?
It depends on your solar system size, your driving patterns, and how much surplus you generate. A 4kWp system in the UK generates roughly 3,500–4,000kWh per year. If 30–50% of that can be used to charge your EV, that's 1,000–2,000kWh of free charging — worth £250–500 at standard tariff rates.
Can I charge from solar overnight?
Not directly — solar panels don't generate at night. However, adding a battery storage system (like a Tesla Powerwall or GivEnergy battery) allows you to store daytime surplus and use it overnight for EV charging. Combine with an off-peak grid tariff for any remaining shortfall.