MAILBOX: Off-Grid EV Charging

Intermediate
Elizabeth and Steve Willey charge their Zero S electric motorcycle with an off-grid PV system.

I very much appreciated Home Power’s coverage of the electric car market (“The Next Wave of Electric Vehicles” by Bradley Berman in HP180). However, I think you should also focus articles on charging an electric vehicle from an off-grid PV system.

I drive a Zero electric motorcycle that recharges with about 15 amps at 120 VAC using a standard Level 1 (slowest) charger, provided by my 3 kW PV system. Larger off-grid PV home systems could possibly accommodate Level 2 charging—up to 30 A at 240 VAC. Or a dedicated stand-alone PV system could be used only for vehicle charging.

There are some important considerations to sizing a solar-electric system to support even minimum charge requirements. For example, to avoid depleting the battery, a 3 kW off-grid PV array with a 15 to 20 kWh battery bank can charge a vehicle battery only during peak sun-hours. At this time, solar energy input is sufficient to charge the vehicle. The battery in an electric vehicle is often the same capacity or larger than a house’s system battery. Manually switching on the charger when house batteries are fully charged and the array is in full sunshine makes it all possible.

For practicality, we need products that incorporate a timer and relay on the vehicle-charging outlet to limit charging to peak sun-hours. A small insolation-sensing, time-delay circuit could shut off the charging outlet if cloud cover extends past several minutes. Perhaps some charge controllers that offer a diversion signal could delay the start of vehicle charging until the house battery is fully charged. This might ensure that vehicle charging uses energy directly from the array, and avoids depleting the house batteries.

So far, I’ve found no commercial products that focus on this process. Articles and user reports, ideas, and off-grid EV charging experiences would be cherished by your readers that are already EV users, and could also encourage more EV usage.

Steve Willey • Sandpoint, Idaho

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