Charging an EV With Home Solar

“Fuel your car from your roof” is one of the better arguments for both solar panels and electric cars, and unlike a lot of energy marketing it is broadly true. But the version of it people carry in their heads — sunlight going into the car — is not how a normal home solar system actually works, and the difference matters when you are deciding what to install.

This page does the arithmetic in the open. Every assumption is stated so you can substitute your own numbers, and we will not tell you what solar costs where you live, because that is genuinely local.

Step one: how much energy does the car actually need?

Start here, because it is the number everything else is measured against and it is smaller than most people expect.

The formula is daily miles ÷ efficiency in miles per kWh. We use a reference of about 3.5 miles per kWhfor a mid-size EV throughout this site; check your own car’s figure, since DOE and EPA publish efficiency on the vehicle label in kWh per 100 miles and it varies a great deal between a small hatchback and an electric truck.

Take the middle of that table. Thirty miles a day is roughly 8.6 kWh, or about 257 kWh a month. That is a meaningful addition to a household electricity bill — it is roughly comparable to adding a major appliance running constantly — but it is not an outlandish number, and it is well within the range a residential solar array can produce.

For context on array sizing, DOE’s homeowner guide notes that NREL uses an average residential system size of 7.15 kW DC, with a 3 to 11 kW range, in its analysis. What that produces in kilowatt-hours depends entirely on where you are, which way the roof faces, what shades it and what month it is — which is why DOE points homeowners at the PVWatts tool rather than publishing a single figure. Use it; do not use a rule of thumb from an article.

Step two: the timing problem

Here is the part that gets skipped. Solar generates during the day. Cars, for the most part, are out being driven during the dayand parked at home overnight — which is precisely when generation is zero.

So the mental image of sunlight flowing into the battery is usually wrong. What actually happens on a standard grid-tied system:

1. During the day, the array supplies the house. Surplus is exported to the grid, and you are credited for it under whatever net metering arrangement your utility offers.
2. Overnight, the car charges from the grid like any other load.
3. On the bill, the daytime export credit offsets the overnight consumption.

That is a perfectly good outcome — the grid is doing the job a battery would, for free — but it depends completely on the value of the export credit. DOE is explicit that net metering arrangements and what you are paid for exported power depend on state policy and your utility. Where export is credited at full retail rates, exporting by day and charging by night is economically identical to charging directly from the panels. Where export is credited well below retail, it is not, and self-consumption becomes worth real money.

Step three: what to do about the timing

Three approaches, in order of how sensible they usually are:

Do nothing (often correct)

If your export credit is close to retail, charge whenever is convenient — usually overnight, which is also when time-of-use rates are cheapest. The two effects stack rather than conflict. This is the right answer for a large share of households and it costs nothing to implement.

Shift charging into daylight (cheap, worthwhile if export credits are poor)

If your utility pays little for exported power, self-consuming is worth more than exporting. Charging while the car is home during the day — weekends, work-from-home days, a second vehicle that stays put — captures that value with no extra hardware.

Every charger with an app can schedule this, and a charger with energy monitoring lets you verify what you actually captured rather than guessing. That is where a unit like the Emporia Level 2 earns its keep, and it is a good argument for a smart chargergenerally. Bear in mind that a car cannot charge selectively from “the solar” — it draws from the house supply, and the accounting happens at the meter.

Add battery storage (expensive; rarely justified by charging alone)

A home battery stores daytime generation for overnight use, which does solve the timing problem directly. It is also a substantial purchase, and if the only benefit you count is charging a car that could otherwise charge on cheap overnight grid power, the arithmetic is hard.

Batteries usually justify themselves on other grounds: backup power during outages, or poor export credits combined with expensive peak rates. If those apply to you, an EV strengthens the case. If they do not, buy the panels and skip the battery. And note that this is separate from using the car as the battery — see our bidirectional charging guide for where that technology actually stands.

The charger itself barely matters here

One useful thing to know: your choice of charger has almost no bearing on solar economics. Charging speed determines how quickly energy moves, not how much you need — a car requiring 8.6 kWh requires 8.6 kWh whether it takes one hour or four.

Two second-order effects are worth a mention. First, scheduling: if you are trying to charge during daylight, the ability to set a window matters, and that is an app feature rather than an amperage one. Second, standby efficiency: EPA states ENERGY STAR certified chargers use about 40% less energy in standby, and standby runs 24 hours a day — a small effect, but a free one. Our ENERGY STAR roundup lists the certified units.

What does matter is charging at the right time and knowing what you used, which points at a charger with a schedule and a meter rather than a bigger one. Size the charger on your panel and your car, using our sizing guide, and treat solar as a separate decision.

How to think about the whole decision

The honest framing is that solar is a whole-house decision that an EV strengthens, not a charging accessory.

An EV adds a large, predictable, controllable load. That is close to the ideal profile for a solar investment: it is big enough to matter, it recurs every month, and unlike a refrigerator you can choose when it runs. If you were already close to justifying an array, an EV usually tips it. If you were nowhere near, an EV alone will not get you there.

A sensible order of operations:

1. Work out what charging costs you today with our cost-to-charge guide and what it adds to the monthly bill in this guide. At the EIA’s reported 2025 residential average of 17.30 cents per kWh, 257 kWh a month is a specific, checkable number.
2. Exhaust the free levers first — a time-of-use rate can cut charging cost substantially with no capital at all.
3. Then size an array against your whole consumption including the car, get local quotes, and check what your utility actually pays for exported power. That last number decides more about solar economics than anything on this page.

One thing we will not do is quote you a federal solar tax credit figure, because incentives change and a stale number in an article is worse than none. Check the IRS and your state’s own program directly; our incentives guide covers the separate federal credit that applies to the charger, which is a different program with different rules.