How Many Solar Panels to Power a House?

September 10, 2011 by Ksenya

Once you decide to install a home solar panel system, the first question is: how many solar panels do I need for my house? The number of solar panels needed to run a house depends on the following factors:

Energy Consumption

How much energy do you use per year? Check your electricity bill to get an idea. Electricity is billed by the kilowatt hour. Solar panel energy output is also measured in kWh per square meter of panel surface. The average electricity consumption for a household in the United States is 8900 kWh per year.
A 1kW solar energy system generates almost 1,000 kWh per year in cloudy regions, and almost double in sunny climates. Whether the system generates the stated amount of electricity depends primarily on the amount of solar radiation reaching the solar array. According to the Department of Energy, systems rated between 1 and 5 kilowatts are usually enough to meet the needs of home and small business owners.
How much of your energy do you want to come from solar panels? Some homeowners choose to source only part of their energy from solar panels. Obviously if choosing to go off the grid, you would want to make sure you correctly estimate the amount of energy you use in a year to have enough solar panels!

Available Sunlight

Photo Credit: NREL.gov

But the amount of energy a panel can generate depends primarily on the amount of available sunlight – or solar radiation – in your area. The more solar radiation reaches the panels, the more energy each panel will generate.

To maximize the amount of sun reaching the panels, panels should be mounted on an unshaded south-facing roof. Alternatively, you can mount panels on poles in your yard. You can use the In My Backyard tool from the National Renewable Energy Laboratory to estimate how much electricity solar panels can generate on your roof.

Type of Solar Panels

Once you’ve decided how many watts of solar panels you need, you can choose a type of solar panel based on efficiency – the proportion of sunlight hitting the panel that is converted into electricity.

Essentially, more lower efficiency panels (usually thin film) are needed to produce the same amount of energy as higher efficiency panels (crystalline panels). If you do not have much roof or yard space, then it will likely be necessary to get higher efficiency panels. The table below shows approximately how much roof space needed for panels with different levels of efficiency.