Solar EV Charging: How to Charge Your Car From Your Roof

Solar EV charging means using your rooftop solar generation to fill your car instead of grid electricity. Three approaches, simplest to most sophisticated:

1. Timer-based charging. Schedule charging across the middle of the day. If household consumption is modest, most of the charger's draw comes from your panels. Free, and works with any charger or even the portable cable.

2. Solar diversion (CT clamp). Chargers like the Evnex and myenergi Zappi clip a current sensor at your meter and watch your export in real time. When the house exports, the charger ramps up to absorb the surplus; when a cloud passes or the oven turns on, it ramps down. Maximum solar usage with no thought required.

3. Inverter integration. The Fronius Wattpilot talks directly to Fronius inverters, and SolarEdge charging lives inside the SolarEdge ecosystem, for the tightest possible tracking of generation. Choose these when your inverter brand matches.

An EV typically consumes 15-20kWh per 100km. Whether your roof can cover your driving depends on your system size, your household's daytime consumption, and how often the car is home in daylight.

As a rule of thumb, a 5kW system ($11,000-13,000 installed) generates meaningful midday surplus in most NZ homes once the usual appliances are fed, enough to make a real dent in normal daily driving when the car is home to receive it. An 8-10kW system ($15,000-18,000) gives genuine headroom to run the house, heat the water and charge the car simultaneously.

Two design notes:

• If the car is away at work all day, solar charging only works on weekends and WFH days; a battery or night-rate plan covers the weekday gap.
• If you are buying solar and a charger together, tell the installer about the EV so the system is sized with charging in mind. The marginal panels are the cheapest ones, at $1.70-2.00 per watt.

Two numbers drive the solar charging case in NZ:

• Grid electricity: about 35c/kWh. Charging 15-20kWh per 100km costs roughly $5.25-7.00 per 100km from the grid at standard rates (less on night rates).
• Buyback: 7-12c/kWh. Surplus you divert into the car only "costs" the export credit you gave up: roughly $1.05-2.40 per 100km.

And one number that applies either way: Road User Charges. Light battery EVs pay $76 per 1,000km, which is $7.60 per 100km, however the battery was filled. So the all-in per-100km picture looks like:

Indicative, assuming 15-20kWh per 100km. RUC includes the per-1,000km rate only; a small admin fee (~$12.44 per online purchase) applies when you buy RUC.

Petrol drivers pay their road contribution as fuel excise inside the pump price, so compare like with like: an EV's energy-plus-RUC total against a petrol car's full pump spend. See our RUC guide and the EV vs petrol comparison for the full picture.

Evnex: NZ-made in Christchurch with CT-clamp solar diversion, OCPP 2.0.1 and local support. The default recommendation for NZ solar homes.

myenergi Zappi: the solar-diversion benchmark. Eco+ mode will charge from surplus only, even if that means pausing entirely when clouds roll through. Works with any inverter brand.

Fronius Wattpilot: the right answer when your inverter is Fronius; direct communication means lag-free solar tracking.

SolarEdge: charging inside the SolarEdge ecosystem for homes already on SolarEdge inverters.

Typical installed pricing across the market is $2,500-4,000 with entry promos from about $2,199; the labour component alone runs $800-1,200. Get installed quotes rather than comparing bare unit prices.