Electrical · Lesson 10 of 13Intermediate7 min read

EV Charging, Solar, Batteries and Generators

Homes don’t only use electricity anymore. Many charge cars, make their own power from sunlight, store it in batteries, or keep a generator for outages. Each of these connects to the same panel and wiring you’ve been learning about, and each brings its own safety rules.

Charging an electric car

DOE’s Alternative Fuels Data Center describes three levels of charging:

Level 1 uses a 120-volt AC plug and adds about 5 miles of range per hour of charging, at about 1.9 kilowatts. Many drivers meet their daily needs by charging overnight this way, on an outlet on a dedicated branch circuit near where they park.
Level 2 uses 240 volts at home (208 volts is typical in commercial buildings) and adds about 25 miles of range per hour. Most home Level 2 chargers run at up to 30 amps, delivering 7.2 kilowatts (30 × 240 = 7,200 watts), and need a dedicated 40-amp circuit under the National Electrical Code.
DC fast charging adds about 100 to 200 or more miles in 30 minutes, at up to 500 kilowatts. It needs heavy commercial power, so it’s found along highways, not in homes.

Installing Level 2 at home is a job for a qualified electrician. Some homes don’t have enough electrical capacity, permits may be required, and in many areas a plan must be approved before installation. Charging equipment that’s certified for safety is recommended, and outdoor installations need outdoor-rated equipment. The Cars course explains the car side.

Rooftop solar and inverters

Solar panels are made of photovoltaic (PV) cells that turn sunlight directly into electricity. A single cell makes only about 1 or 2 watts, so cells are wired together into weather-tight panels, and panels into arrays. The best modules today approach 25 percent efficiency, up from under 10 percent in the mid-1980s.

PV cells make direct current, but your home and the grid run on alternating current. Inverters convert the DC to AC. Since 2004, most U.S. PV systems have been grid-connected, wired into the home’s panel and the utility’s lines. Small grid-connected systems, mostly on homes and buildings, made about 93 billion kWh in 2025.

Home batteries

A battery lets a solar system supply electricity when the sun isn’t shining. EIA counts batteries under 1 megawatt as “small-scale,” and many are owned by people who charge them from their own solar panels. In 2021, U.S. utilities in 42 states reported about 1,094 megawatts of small-scale battery capacity. Whether a solar-and-battery system can power a home during a grid outage depends on how it’s designed and installed, so ask the installer.

Every connection to the panel here is a job for licensed or certified professionals. Sources: EIA; DOE Alternative Fuels Data Center; CPSC; OSHA.

Portable generators and carbon monoxide

A portable generator is an engine, and its exhaust contains carbon monoxide (CO), a gas you can’t see or smell. CPSC says more than 80 consumers die each year from CO poisoning caused by portable generators. The official rules:

Use a generator only outside, at least 20 feet from the house, with the exhaust pointed away from the home and other buildings (CPSC, Ready.gov).
Never run it inside a home, garage, basement, crawlspace or shed, even with doors and windows open (CPSC).
Install battery-operated CO alarms, or plug-in alarms with battery backup, outside sleeping areas and on each floor (CPSC). If a CO alarm sounds, get outside immediately, then call 911.
Keep the generator dry, and plug appliances into it with heavy-duty, outdoor-rated, grounded cords rated for the load (OSHA, CPSC).

Backfeeding and transfer switches

Never try to power a house by plugging a generator into a wall outlet. CPSC and OSHA both warn against it. Connecting a generator to a building’s wiring without a properly installed transfer switch can send power back out through the wiring, a hazard called backfeeding. OSHA warns that it can energize wiring for great distances, creating a risk of electrocution for utility workers and others in the area.

The safe way to connect a generator to a home’s circuits is a transfer switch, which disconnects the house from the utility before connecting the generator. OSHA says never to attach a generator to a structure’s electrical system unless a qualified electrician has installed it with a transfer switch.

Standby generators

A standby, or stationary, generator is installed permanently outside and connected to the home through a transfer switch, often an automatic one that starts the generator when the power fails. CPSC staff say these are typically installed by licensed tradespeople following the National Electrical Code and the maker’s instructions, and must meet local codes. They still make CO. In a June 2025 report, CPSC staff found exhaust traveling at least 25 feet from generator enclosures and concluded that the 5-foot clearance from openings allowed by the NFPA 37 standard is not enough to keep CO out of homes.

Parts and what they do
Part	What it does	Signs of trouble
Level 1 charging cord	Charges an EV from a 120-volt outlet.	Warm plug or outlet: stop and have it checked.
Level 2 charger (EVSE)	Charges an EV at 240 volts on a dedicated circuit.	Breaker trips; damage to the cable or connector.
Solar panels (PV)	Turn sunlight into DC electricity.	Damaged panels or wiring: call the installer.
Inverter	Converts DC from panels or batteries to AC.	Error lights or messages.
Home battery	Stores energy for later.	Swelling, heat or warning messages: call the installer.
Portable generator	Engine-driven backup power, used outdoors only.	Used indoors or near openings: deadly CO.
Transfer switch	Switches the house safely between utility and generator.	No transfer switch means a backfeed risk.
Standby generator	Permanent backup generator outside the home.	Exhaust near windows, doors or vents.
CO alarm	Warns of carbon monoxide.	Needed whenever a generator or fuel-burning appliance is used.

StopLicensed work, every one

Installing a Level 2 charger, solar panels, a home battery, a transfer switch or a standby generator means connecting to your panel. All of it belongs with licensed or certified professionals, usually with permits and inspections. Never connect a generator to house wiring through an outlet, and never run one indoors or near windows, doors or vents.

Check yourself

Tap an answer to check it, or open “Show the answer.”

About how many miles of range does Level 2 home charging add per hour, according to AFDC?
Show the answer
About 25. Level 2 at 240 volts adds about 25 miles per hour; Level 1 at 120 volts adds about 5.
What does a solar inverter do?
Show the answer
Converts the panels’ DC into AC. PV cells make DC, and inverters turn it into the AC used by homes and the grid.
How far from the house does CPSC say a portable generator must be?
Show the answer
At least 20 feet, outside only. Outside only, at least 20 feet away, with the exhaust pointed away from the home.
Why is plugging a generator into a wall outlet dangerous to utility workers?
Show the answer
It can backfeed power through the transformer onto the lines they’re repairing. Backfed power can energize lines for great distances, creating an electrocution risk.
What device lets a generator power a home’s circuits safely?
Show the answer
A transfer switch installed by a qualified electrician. A transfer switch disconnects the house from the utility before connecting the generator.

Go deeper

U.S. Department of Energy, Alternative Fuels Data Center: Electric Vehicle Charging Stations Charging levels, connectors and speeds.
U.S. Department of Energy, Alternative Fuels Data Center: Charging Electric Vehicles at Home Charging at home: permits, electricians and safety.
U.S. Energy Information Administration: Solar Explained, Photovoltaics and Electricity How solar cells make electricity.
U.S. Consumer Product Safety Commission: What to Know About Generators and Carbon Monoxide (Publication 468) CPSC on generators and carbon monoxide.
OSHA Fact Sheet: Using Portable Generators Safely (FS-3286) OSHA’s fact sheet on using portable generators safely.
The Trades, Cars, Lesson 11: Hybrids and Electric Cars Hybrids and electric cars, from the Cars course.
Being an Adult 101: Test Smoke and CO Alarms Test smoke and CO alarms.

Sources

I finished this lessonSaved on this device only.

A free course from Teddy Rook Book. It explains how home electrical systems work in general and follows U.S. sources; your local electrical code, your inspector and a licensed electrician are the final word for your home.