Charging an electric car with solar panels

An electric car turns your driveway into a second appliance room, and one that uses a surprising amount of power. Pairing it with solar is a natural idea, and for many households it works well. It does need a bit of planning, because cars charge when the sun is often down and drive hardest in the months when panels produce least. This guide sits in our batteries and backup power hub since the timing questions are the same ones storage tries to solve.

How much energy does an EV use?

Efficiency varies with the car, but a common range is about 15 to 25 kWh per 100 km, with colder weather pushing it up. Someone driving 15,000 km a year at 18 kWh per 100 km uses about 2,700 kWh. A commuter doing 25,000 km could pass 4,000 kWh. Compare that with a typical Canadian household’s 9,000 to 12,000 kWh a year, and you can see an EV may add a quarter to a third to your electricity use, sometimes more.

Those are estimates. Your own odometer and your car’s efficiency display will give better numbers, and charging losses add a bit on top.

How many extra panels?

A kilowatt of solar in southern Canada often yields roughly 1,100 to 1,400 kWh a year, depending on location and design. To cover 2,700 kWh you need about 2 to 2.5 kW of added capacity, which means five to six modern 400 to 450 W panels. A longer commute might need eight or more.

These are rough planning numbers. Your roof space may limit what is possible, and our guide on how many solar panels you need explains how to size the whole system.

The cheapest moment to add panels is when the main system is being designed. Adding them later means another visit, and the inverter or electrical panel may already be at capacity. If you do not own the car yet but expect to within a few years, say so when you collect quotes.

The timing problem

Solar output peaks around midday. Many people plug in when they arrive home in the evening and charge overnight, after the sun has set. There are three ways to deal with that.

The first is net metering or a similar credit scheme. Your panels send surplus power to the grid in the afternoon and you draw it back at night. In provinces where credits are near the retail rate, this works almost like using solar directly. Our explainer on net metering in Canada covers how the rules differ, and these rules are changing in some provinces, so check with your utility.

The second is to shift charging to daytime. This works if you work from home, park at home on weekends, or use a charger with scheduling. Some smart chargers can follow surplus solar generation and slow down when a cloud passes.

The third is a battery. It adds cost, and it rarely makes sense just for EV charging, but where time-of-use rates are steep it can help. See time-of-use rates and solar for how that works.

If your credits are lower than retail, as in net-billing style arrangements, charging during the day matters more because every kWh you use directly is worth more than one you export.

Winter changes both sides

Cold weather reduces EV range, often noticeably, because of battery chemistry and cabin heating. At the same time, panel output in December and January is a fraction of the summer peak. You can see the pattern in solar output by month in Canada. Most owners accept this and let summer surpluses and the grid cover winter, rather than building an array big enough for January.

Panels do enjoy cold, clear days, since low temperatures slightly raise their efficiency. Snow cover is the real issue, and it usually clears quickly on tilted panels.

The electrical side

A Level 2 home charger commonly draws 7 kW or so, which is a big new load on your panel. Your electrician will check whether the service has enough spare capacity, or whether a load-management device can let the charger and the rest of the house share. A solar system does not remove that need, because the grid still supplies peak demand on cloudy evenings. Permits and inspection apply to charger installations as well as to solar.

Ask your installer whether the inverter can handle future additions, and whether the system can talk to a smart charger. Rebates for chargers and for EVs have existed federally and provincially in recent years, but terms change often, so verify current programmes before you buy.

Is it worth it?

Charging a car on your own solar power replaces fuel spending, which is often a larger bill than electricity for the same distance. For many homes that improves the overall economics of solar, because the extra panels have a ready use for the energy. Run your own numbers, include winter, and keep expectations modest.