How many solar panels do I need for my house?

Jess Hutton | January 21, 2016 | Industry Knowledge

One of the most commonly asked questions in the solar industry is, “How many solar panels do I need for my house?” There are several contributing factors to consider when determining the answer, including
– What is the daily average energy usage of your home?
– Do you want to live completely off the grid?
– Which direction is your roof facing?
– How many hours of sunlight does your area receive each day?

Let’s walk through each of these factors.

Household Energy Consumption

The first step in defining how many solar panels you need is figuring out the average amount of power your home consumes. A typical house in the U.S. will use either electricity or gas to heat the home, heat water, power the oven and appliances, and use lights. If you do not know how many kilowatt-hours (kWh) your house uses on a daily basis, take a look at a past electricity bill.  If it does not show a daily average, simply divide the monthly average by 30 (or the annual average by 365). The more energy a house consumes, the more solar panels will be required.

The Grid

Another determining factor in understanding how many solar panels your home needs is defining whether your goal is to go totally off the electricity grid or partially off- grid.  You will need to make sure you correctly estimate the amount of energy your home uses in a year to ensure you have enough solar panels to power your specific needs.  If you are trying to go completely off- grid, you will need a way to store the solar energy collected during the day for night usage.  Learn more about home energy storage.

South-Facing Rooftops

To maximize the amount of sun reaching the solar panels on your home, the panels should be mounted on the south-facing section of the roof with no shade. Obstruction from trees or tall buildings can affect the amount of kWh generated and you will probably require more solar panels to meet your targeted energy goals.

Dave Dugdale/Flickr

Local Available Sunlight

Another key variable is the climate in your city and the amount of sun exposure that your home receives. If you live in a very sunny location like Sacramento, CA, you will need less panels than if you live in a cloudy city such as Juneau, Alaska.

The easiest way to accurately find out how many panels you will need for your home is to have a solar expert analyze your roof architecture, the angles of your roof to the sun, and your typical energy usage and goals. However, you can determine approximately how many solar panels will fit on your roof with the following calculations:

The average solar panel is approximately 3 feet by 5 feet (total of 15 square feet), which produces around 190 watts of electricity (0.19 kW per panel). Take the square footage of your south-facing rooftop and divide by 15.

Let’s say you have 510 square feet. You would divide this number by 15.

510 / 15 = 34

With 510 square feet, 34 solar panels would fit on your roof.

How much energy would these panels be rated to produce?

34 x 0.19 = 6.46 kW

In this example, a 510 square foot roof would fit 34 solar panels and produce 6.46kW*.
*numbers are rough estimates

To accurately determine how much energy these panels will produce depends on several of the factors as discussed above. A solar professional will be able to take the guess work out of the equation and accurately identify a solar system that will work for your home and your energy needs.

What other questions do you have about solar panels for your home?  Please comment below so we can help!

Featured photo by Micolo J/Flickr


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