For homeowners considering the transition to solar energy, a common query arises: “How many solar panels do I need to power my home?”
The primary aim of any solar installation should be to achieve 100% electricity offset and maximize savings. It’s not about fitting as many panels as possible on your roof. The number of panels required depends on:
- Electricity Consumption
- Sun exposure
- Solar panel power rating
To get a clearer picture of how many panels you might need, follow this basic equation:
Solar panel wattage x peak sun hours x number of panels = daily electricity use
Using national averages:
- Daily Electricity Use: According to the U.S. Energy Information Administration (EIA), the average US household in 2021 consumed 10,632 kilowatt-hours (kWh) annually. This translates to:
- 886 kWh/month
- ~30 kWh/day
- Peak Sun Hours: Divide the daily usage by the average peak sun hours for your city. For our example, we’ll use 5 peak sun hours:30 kWh/day ÷ 5 peak sun hours = 6 kW
- Panel Power Rating: Divide the result by the power rating of each panel. Using a common rating of 400W or 0.4 kW:6 kW ÷ 0.4 kW = 15 panels
Your electricity consumption can be found on your utility bills. To determine your daily usage, divide the total monthly consumption by the number of days in the month. For a more accurate estimate, average out several months.
Peak Sun Hours
The amount of sunlight your location receives, termed as peak sun hours, plays a crucial role. A peak sun hour is when solar irradiance averages 1,000 watts per square meter or 1 kW/m^2. In the US, this varies from over 5.75 hours/day in the Southwest to less than 4 hours/day in the northern regions. To find your city’s average, Google “Peak sun hours in [your city]” or refer to a peak sun hours map.
Solar Panel Power Rating
Solar panels come with different power ratings, typically ranging from 250W to 450W. The most popular is 400W, offering a balance between output and cost. Depending on your roof space and budget, you can choose a rating that suits your needs. For this example, we’ll use 420W panels.
Using the equation:
Daily electricity consumption ÷ peak sun hours ÷ panel wattage = number of solar panels
For our example:
30 kWh ÷ 5.2 peak sun hours ÷ 420W = 13.7 panels
Rounding up, you’d need 14 solar panels for a 100% electricity offset.