Charging an EV with Home Solar: What to Know Before You Size Your System

If you already own or are planning to buy an electric vehicle, it changes your solar sizing calculation meaningfully — and it's worth telling your installer upfront rather than discovering the gap later.

How much extra usage an EV adds

A typical EV driven an average annual mileage (roughly 12,000 miles/year) adds somewhere in the range of 3,000-4,500 kWh of annual electricity usage, depending on the vehicle's efficiency and your driving habits — often a 25-40% increase over a typical household's baseline usage. If you're planning an EV purchase within the next few years, size your solar system for that future usage now rather than adding panels later (which is more expensive per watt than doing it in one project).

Timing your charging matters

If your utility has time-of-use rates, charging your EV during solar production hours (midday, if you're usually not driving) captures the most direct value from your panels. Charging overnight, as most EV owners default to, means you're drawing from the grid (or from stored battery power, if you have one) rather than directly from your panels — which is fine financially under retail-rate net metering, but changes the case for a battery under weaker export-rate states.

Should you add a battery specifically for EV charging?

In states with strong retail-rate net metering, it's usually not necessary purely for EV charging — you can export daytime surplus and draw credited grid power at night for charging. In states with weak export rates (like California under NEM 3.0), a battery sized to also cover evening EV charging can improve the economics of both the battery and the EV charging cost together.

What to tell your installer

Give them your EV's estimated annual mileage (or your current one's actual usage if you already own it) upfront, and ask them to size the system including that load — not just your household's existing electric bill, which will understate your real future usage.