How to Read Your Household Electricity Use Before Going Solar

Before you invest in a home solar system, the most important number to understand is your household electricity use. The size of the solar array you need depends directly on how many kilowatt-hours (kWh) your home consumes over a year. This guide, part of our home solar planning series, walks you through reading your electric bill, identifying what drives your consumption, and using that data to plan a solar installation that fits your actual needs.

Understanding kilowatt-hours on your electric bill

The U.S. Energy Information Administration (EIA) explains that electricity is measured in units of power called watts. One kilowatt (kW) equals 1,000 watts. Because power is instantaneous, utilities bill you for energy consumed over time, measured in kilowatt-hours (kWh). One kWh is the energy of one kilowatt used for one hour. For example, a 40-watt light bulb left on for five hours uses 200 watt-hours, or 0.2 kWh.

Your monthly electric bill shows total kWh used during the billing period. The EIA notes that utility companies measure this with meters, typically located where the power line connects to your home. Many utilities now use electronic smart meters that wirelessly send usage data in real time, and some advanced meters can even track the electricity use of individual devices.

What uses electricity in a typical U.S. home

According to the EIA’s Residential Energy Consumption Survey, the average U.S. household consumes about 10,500 kWh of electricity per year. However, this figure varies widely by region and housing type. Single-family detached homes in the South tend to use the most electricity, while apartments in the Northeast use the least. Homes in the South are more likely to have electric heating and use more air conditioning.

The three largest categories of residential electricity consumption in 2020 were air conditioning (19%), space heating (12%), and water heating (12%). Lighting and refrigerators are the next two largest end uses. Air conditioning has been one of the fastest-growing uses; in 2020, about 89% of U.S. homes used air conditioning, up from 57% in 1980.

Refrigerators are nearly universal, with 99% of homes having at least one. In 2020, 34% of homes had two or more refrigerators, and separate freezers were common, especially in the Midwest. The EIA notes that a second refrigerator or a standalone freezer adds to overall consumption, so it is worth counting all cooling appliances when you tally your usage.

Gathering 12 months of usage and noting seasonal peaks

Because heating and cooling drive large seasonal swings in electricity use, a single month’s bill is not enough to size a solar system. Collect at least 12 consecutive months of bills, or download the data from your utility’s online portal. Look for the total kWh used each month and the annual sum. Note which months have the highest consumption; for many homes, summer air conditioning or winter electric heating creates a pronounced peak.

Smart meter data can make this task easier. The EIA states that many utilities now use electronic smart meters that wirelessly send usage data in real time. If your utility shares that data with you, it helps you see when you use the most electricity and whether your usage aligns with the sunniest hours, a key factor for solar production.

Estimating individual appliance energy use

The Virginia Cooperative Extension guide on estimating appliance energy use offers a straightforward formula: (Wattage × Hours Used per Day ÷ 1000) = Daily kWh consumption. Multiply that by the number of days the appliance is used per year to get annual kWh. Find the wattage on the appliance’s nameplate, usually stamped on the bottom or back. If only amperes are listed, multiply amps by volts. Most household appliances in the United States use 120 volts; larger appliances like clothes dryers and electric cooktops use 240 volts.

Many appliances continue to draw a small amount of power when switched off. The Virginia guide calls these “phantom loads” and says they occur in televisions, computers, kitchen appliances, and other electronics. Unplugging appliances or using a power strip with a switch can eliminate these loads. For refrigerators, the guide recommends dividing the total time the appliance is plugged in by three to estimate actual operating hours, because the compressor cycles on and off. The guide also provides typical wattage ranges: a clock radio might use 10 watts, a microwave oven 750 to 1,100 watts, and a water heater 4,500 to 5,500 watts.

Planning for changes: new appliances or electric vehicles

Your solar system should be sized for your future electricity use, not just your past bills. If you plan to add an electric vehicle, install a heat pump, or replace an aging refrigerator, your consumption will change. The Virginia Cooperative Extension formula can help you estimate the additional load: find the new appliance’s wattage, estimate daily hours of use, and calculate the annual kWh. Add that to your current annual total to arrive at a target for your solar array. A licensed electrician can also help you assess whether your home’s electrical panel can accommodate new large loads, which is a separate but important step before going solar.

Connecting your usage to solar system sizing

Once you have a solid annual kWh figure, you can estimate how much solar capacity you need. The PVWatts Calculator, run by the National Laboratory of the Rockies, is an online tool that estimates the energy production of a grid-connected photovoltaic (PV) system. You enter your location, the system size in kilowatts, the array type, tilt, and azimuth, and the calculator uses 30 years of local weather data to project monthly and annual output in kWh. By comparing your annual consumption to the production estimates for different system sizes, you can find a size that offsets the portion of your usage you want to cover. For a deeper dive, see our guide on home system sizing.

Solar panels produce the most power during sunny hours, while your home may use electricity around the clock. If your utility offers net metering, excess daytime production can offset evening and nighttime consumption. Understanding your usage patterns helps you decide whether adding a home battery storage system makes sense to store solar energy for later use.

Key data points for sizing your solar system

For more step-by-step planning advice, visit our how to plan a home solar system guide, which covers the entire process from energy analysis to installation.

Frequently asked questions

How many months of electric bills do I need before going solar?

You should collect at least 12 months of bills to capture the full seasonal variation in your electricity use. The EIA data shows that heating and cooling can cause large swings from month to month, so a full year gives the most accurate baseline for sizing a solar system.

Can I use my smart meter to see real-time usage?

Yes. According to the EIA, many modern smart meters wirelessly send usage data in real time, so ask your utility what usage data it makes available to customers. Detailed data can help you spot high-use periods and verify the impact of energy-saving changes.

Does the PVWatts calculator work for any location in the U.S.?

The PVWatts site says its expected range is based on 30 years of actual weather data at the given location, and it cautions that its predictions include many inherent assumptions and uncertainties. Use it as a planning estimate and ask an installer for a site-specific one.

For more guidance on understanding your household electricity use before installing solar, visit our Household Energy Use category page.

Sources

• U.S. Energy Information Administration: Measuring electricity
• U.S. Energy Information Administration: Electricity use in homes
• Virginia Cooperative Extension: Estimating Appliance and Home Electronic Energy Use
• PVWatts Calculator (National Laboratory of the Rockies)