Combining a home solar panel system with an EV charger is among the most effective ways to maximise the financial return on both investments. An EV charged from grid electricity at current rates costs around 24–28p/kWh. An EV charged from solar-generated electricity costs near zero per kWh (once the panels have paid back their installation cost). A household with both a solar installation and an EV — and the right equipment to direct solar generation into the car — can significantly reduce the combined running costs of their electricity and transport.
How Solar-to-EV Charging Works
Standard home EV chargers operate at a fixed charge rate — typically 7.4kW (32A, single phase) for a home wallbox. A 4kWp solar system generates a maximum of around 4kW at peak — not enough to power a 7.4kW charger directly from solar alone. Without solar-aware charging, the EV charger draws from the grid whenever it is connected, regardless of whether the panels are generating. Solar-aware EV charging (sometimes called solar divert or smart solar charging) requires an EV charger that can communicate with a solar monitoring system to vary its charge rate in real time, consuming only the excess solar generation available at any moment.
"The solar divert function on a smart EV charger is not a marketing feature — it is the mechanism that makes solar-to-EV charging actually work at domestic scale. Without it, you are effectively choosing between charging your car or exporting your solar to the grid. With it, your car becomes a large battery that absorbs surplus generation throughout the day. On a summer day with a 4kWp system and a car parked at home, a solar-aware charger can put 15–20 kWh into the car directly from solar generation."— Energy Saving Trust — Solar and EV Integration
Equipment Required for Solar-to-EV Integration
Solar-aware EV charging requires: a solar inverter that exposes real-time generation and consumption data via a compatible API or communication protocol; an EV charger that can read this data and modulate its charge rate accordingly (minimum charge rates are typically 1.4kW, meaning a minimum of around 6A export is needed to trigger solar charging); and optionally a battery storage system that can also participate in the energy management. Key compatible combinations include: SolarEdge inverter with Zappi EV charger; GivEnergy inverter and battery with Ohme or Zappi; Solis inverter with Zappi. The Zappi charger by myenergi is the most widely compatible solar-aware charger in the UK market.
System Sizing for Solar-to-EV
Adding EV charging to the self-consumption load significantly changes the optimal solar system size. A household consuming 4,000 kWh/year in the house, plus 3,000 kWh/year in the car (typical for 10,000 miles at 3 miles/kWh), has a combined annual electricity consumption of 7,000 kWh. A solar system sized to cover this would need to be 7–8kWp in the south of England — substantially larger than the 4kWp system that would cover household use alone. Battery storage becomes more valuable in this scenario: it bridges the gap between daytime generation and evening/overnight EV charging requirements.
"The EV changes the solar sizing calculation entirely. A household without an EV that installs a 4kWp system in the south east is close to optimal for their consumption profile. The same household, when they buy an EV, suddenly has a consumption load that could absorb another 4–5kWp of generation profitably. Sizing the solar system with the EV in mind from the start — or specifying a larger inverter that can accommodate additional panels later — is worth the conversation with the installer."— Which? — Solar Panels and EV Charging
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