Why Charge Your EV with Solar?
Charging an electric vehicle from the grid is already cleaner than burning petrol. But charging from your own rooftop solar panels takes it a step further — you're driving on sunlight you generated yourself, at near-zero marginal cost per kilometre. Over time, the combination of solar panels and an EV can deliver substantial savings on both fuel and electricity bills.
What You Need: The Essential Components
- Solar panel array: For most EVs, a 5–10 kW rooftop system is a sensible starting point. Larger arrays generate more surplus to divert to your car.
- Solar inverter: Converts DC power from your panels into AC power your home and charger can use. String inverters work well for simple setups; microinverters suit complex roofs.
- EV charger (EVSE): A dedicated Level 2 home charger (7–22 kW) is strongly recommended over a standard wall socket for regular use.
- Smart energy management system (optional but powerful): Devices like the myenergi Zappi or similar "solar-divert" chargers detect surplus solar generation and automatically prioritise charging your car before exporting to the grid.
- Home battery (optional): A battery like a Tesla Powerwall lets you store midday solar surplus and use it to charge your car in the evening.
Sizing Your Solar Array for EV Charging
A useful rule of thumb: every additional kilowatt-peak (kWp) of solar capacity generates roughly 800–1,200 kWh per year in a moderately sunny climate. Most EVs consume around 15–20 kWh per 100 km. So if you drive 15,000 km per year, you need approximately 2,250–3,000 kWh annually just for the vehicle — meaning a dedicated 3–4 kWp addition to your existing array could cover most of your EV charging needs.
Solar Divert Charging: The Smart Approach
The most cost-effective solar EV charging strategy is solar divert: using a smart charger that monitors your solar generation in real time and throttles EV charging up or down to match your solar surplus. This way, excess solar that would otherwise be exported to the grid at a low feed-in tariff is used to power your car instead.
- Panels generate power throughout the day.
- Home loads (fridge, lights, etc.) are met first.
- Surplus flows to the EV charger automatically.
- Any remaining surplus is exported to the grid.
Grid-Tied vs. Off-Grid Solar EV Charging
| Feature | Grid-Tied | Off-Grid with Battery |
|---|---|---|
| Upfront cost | Lower | Higher |
| Charges on cloudy days | Yes (from grid) | Limited by battery capacity |
| Running cost per km | Very low | Near zero |
| Energy independence | Partial | High |
| Complexity | Low | Higher |
Getting Started
The simplest path: install or expand a rooftop solar system and add a smart solar-divert EV charger. Even without a home battery, you can shift a meaningful portion of your EV charging to solar-generated electricity — especially if you're home during the day or can schedule charging during peak solar hours.
Speak with a certified solar installer about your roof's orientation, shading, and your driving patterns before sizing the system. A well-designed setup can pay for itself over a reasonable timeframe while cutting your transport emissions significantly.