Planning Solar for EV Charging

Start with miles and wall energy—not charger capacity

A Level 2 charger capable of delivering several kilowatts does not draw its maximum output every hour of the year. It supplies energy when a connected vehicle requests it, subject to the vehicle, circuit and charging settings. Estimate annual driving first. Then use the specific vehicle's observed miles per kWh or kWh per 100 miles and account separately for energy drawn at the wall.

For example, a planning case of 10,000 miles at 0.30 kWh per mile equals 3,000 kWh delivered to the vehicle before charging losses. This is arithmetic, not a prediction for a California driver. A proposal should show its annual miles, vehicle efficiency and loss assumption so each can be changed. If the owner has several months of home-charger or vehicle-app history, annualize that measured wall energy cautiously and explain seasonal or driving changes.

Separate vehicle efficiency from charging losses

The dashboard's driving-efficiency figure may describe energy leaving the traction battery, while the electric meter records energy entering the home. Conversion, battery conditioning and other charging overhead can make wall energy higher. Do not hide that difference inside an unexplained oversizing factor. Use measured charger data when available, or label a planning allowance as an assumption rather than a vehicle specification.

Temperature, speed, elevation, payload, climate control and driving style can change vehicle energy use. Plug-in hybrids add another variable because some miles may use gasoline. Build a base case around representative driving, then include a higher-use case for long commutes, frequent highway travel or a second driver. A credible solar proposal keeps the vehicle's battery capacity, charging power and annual energy demand as three different quantities.

Check whether the EV is already in the utility history

Twelve months of electric bills may already include some or all of the vehicle charging. Adding a full annual EV estimate on top of that history would count the same energy twice. Mark the date the vehicle arrived, the months represented in the bill data and whether charging occurred mostly at home. If six months are already present, estimate only the missing portion unless driving will materially change.

The reverse problem also occurs. A newly ordered EV may not appear in any bill, or a driver may currently charge at work and plan to shift home. Keep historical household use and future vehicle use in separate columns. If interval data is available from the utility portal, compare charging sessions with overnight or daytime load changes. Documented adjustments are more useful than multiplying total household consumption by a generic percentage.

Map where and when the vehicle will charge

Solar production and vehicle charging overlap only when the car is connected and requesting energy while the array is producing. A commuter who leaves before sunrise and returns in the evening may have little direct daytime overlap on weekdays. A remote worker, weekend driver or household with a midday return can have a different pattern. Workplace and public charging reduce the energy that must be supplied at home.

Create a seven-day charging schedule using typical arrival time, departure time, miles replenished and any workplace or public sessions. Note whether the car or charger can delay charging. Department of Energy guidance says most EV owners charge at home, while public and workplace charging can extend useful range. The design should model the schedule the household can actually follow, not assume every EV kilowatt-hour is served directly by rooftop solar.

Choose charging equipment around the duty cycle

The California Energy Commission describes Level 1 charging as 120-volt charging that generally adds about five miles of range or less per hour. Level 2 uses 208 to 240 volts and can add roughly 14 to 35 miles per hour, depending on the equipment and vehicle. Those ranges help frame the decision, but the necessary charging power depends on how many miles must be restored during the available parking window.

A driver replenishing a modest commute over a long overnight stay may not need the highest available circuit. A household with two vehicles, short turnaround times or irregular long trips may need a different plan. Confirm the vehicle's onboard charging limit, connector, circuit rating and installation requirements. Faster equipment does not reduce the annual kWh required for the same driving, and it does not by itself justify a larger solar array.

Compare direct solar charging with scheduled off-peak charging

Daytime charging can increase direct use of solar production, reducing the amount exported before electricity is later imported for the car. Overnight charging may align better with a utility's low-price period even though the vehicle is then using grid energy or energy previously stored in a home battery. The better schedule depends on the actual tariff, export credits, household loads, battery objectives and parking availability.

Under California's Net Billing Tariff, import prices and export credits can vary by time, and exported solar is not generally credited at the same value as retail imports. A model should therefore show energy used directly, energy exported, grid energy imported for charging and any battery flow. Do not describe annual solar generation equal to EV consumption as if every mile is physically powered by simultaneous sunshine.

Verify the serving utility, CCA and current rate

California does not have one universal EV rate. PG&E currently describes EV2-A as a whole-home time-of-use plan and EV-B as a separately metered option; it also lists E-ELEC for qualifying electrified homes. SCE identifies TOU-D-PRIME for eligible homes with an EV, battery or qualifying heat-pump load. SDG&E publishes EV time-of-use options and places residential Solar Billing Plan customers on EV-TOU-5. Municipal utilities use their own tariffs.

A community-choice aggregator may supply generation while the incumbent utility delivers power and meters the account. Record both providers from the current bill. Before changing rates, use the utility's comparison tool or current tariff and consider all household loads, not only the EV. A lower overnight price can be accompanied by different peak prices, fixed charges or other terms. Current utility documents and the final account election control.

Size solar with scenarios instead of a single guess

Add the EV planning load to the home's measured annual and seasonal use, then compare at least three cases: present driving, a reasonable higher-mileage case and any documented second vehicle. Keep other planned loads—such as a heat pump, water heater, pool or accessory dwelling unit—separate so the proposal shows what each change contributes.

Next, test whether the usable roof area, shade, orientation and interconnection limits can support the proposed array. NREL's PVWatts can provide an independent production reasonableness check using location and disclosed system assumptions, but it is not a bill model, permit approval or guarantee. Monthly production matters because driving and solar output can vary by season. If the roof cannot support every future load, show the expected grid purchases instead of implying that an oversized forecast will disappear.

Coordinate the charger, panel, solar and battery design

An EV charging circuit is part of the home's electrical system. The responsible licensed professionals should evaluate the service rating, main panel, feeder, continuous loads, available capacity, charger circuit and the proposed solar and storage equipment. A load-management system may be an option in some designs, but its controls, limitations and code treatment must be specified rather than assumed.

California has a statewide EV-charging permit-streamlining framework, while each city or county administers its process. GO-Biz maintains a jurisdiction map and permitting guidebook; that does not mean every project is permit-free or automatically approved. Ask who obtains the charger permit, whether the solar and charger are submitted together or separately, and whether a utility service upgrade is required. Include the price and schedule effect of any panel or service work before accepting the energy proposal.

Treat a home battery and an EV battery as different resources

A stationary battery may shift some midday solar into evening charging, but its usable kWh, output power, reserve and efficiency limit how much. Charging a vehicle can consume a large share of stored energy that might otherwise support refrigeration, lighting, communications or medical equipment during an outage. Define whether bill management, home backup or emergency vehicle charging has priority.

Do not assume the EV can power the house. Vehicle-to-home and bidirectional charging require a compatible vehicle, charging equipment, controls, electrical design, permits and utility treatment. Ordinary Level 1 or Level 2 equipment does not create that capability. If bidirectional operation is important, require the exact supported configuration and written responsibilities. Otherwise, model the car as a load and the stationary battery as a separately constrained resource.

Plan explicitly for two vehicles and changing routines

A second EV does not automatically double the solar requirement. The vehicles may travel different distances, charge at different locations or share one circuit through scheduled or managed charging. Build a separate row for each vehicle: annual miles, observed efficiency, home-charging share, arrival window and expected purchase date. If the second vehicle is speculative, keep it as an optional case rather than embedding it in the base proposal.

Also test changes in employment, school, retirement or a move from workplace to home charging. Public fast charging can cover occasional trips without becoming a dependable home-energy plan, and its price is separate from the utility bill. The homeowner should be able to see the result if miles rise, workplace charging ends or the second vehicle is delayed. Scenario labels prevent future possibilities from being presented as measured current demand.

Use a decision-ready EV and solar checklist

Before approving a design, record the vehicle model, annual miles, observed or specified efficiency, charging losses, home-charging share, charger power, circuit, weekday and weekend schedule, utility, CCA, current rate and proposed rate. Add twelve months of household kWh, interval data when available, documented future loads, roof production assumptions, direct solar use, exports, grid imports, battery operation and remaining utility charges.

Ask the proposal to distinguish measured facts, current published rates and forecasts. Confirm the equipment, permit owner, service-upgrade scope, appropriately licensed installation contractor and change-order process in the final documents. For a lease or PPA, compare the complete payment schedule plus estimated utility charges; for a purchase, include upfront or loan costs and service responsibilities. The goal is an auditable plan for the household—not a universal claim that a certain number of panels covers every EV.

Apply this to your California home

Compare the matching $0 down solar in California page, the Axia by Qcells pathway and Qcells equipment. Local permit and utility questions are covered in our Irvine, Anaheim and Orange County pages.