How many solar panels does it take to power a house?

Writer Cris Carl interviewed solar panel expert Gregg Garrison to get the answer.

Posted by Cris Carl | May 18, 2011
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jbolhuis/stock.xchngWhile there are many factors involved in determining how many solar panels to use to power your home, there is a basic formula. Gregg Garrison, general manager of Northeast Solar in Hatfield, MA, suggested some guidelines for the average homeowner regarding the number of panels to power both electrical and hot water needs.

How many solar panels for an average household?

Garrison said that the average home is approximately 1,500 square feet and has electrical costs of about $100 per month.  Garrison said that such a house generally needs about 16 panels to completely cover electrical power needs. 

If you are looking to heat water for the average family of four, two solar thermal panels would be needed, Garrison said. “The average hot water consumption is off-set by about 70 percent.”

What’s the difference between photovoltaic panels and solar thermal panels?

The cells in photovoltaic panels generate electrical power by converting solar radiation (sunlight) into an electrical current. Photovoltaic (PV) cells are made of a variety of materials that include several types of silicon, arsenic and selenium.

Solar thermal panels are a closed system of tubes that contain a solution similar to antifreeze. Solar thermal panels collect solar heat and transfer it to hot water tanks. Garrison said that electrical hot water tanks work the best for solar hot water use.  DIY Resource:

What affects the number of solar panels you will need to power your house?

Depending on what direction your house is situated – north/south or east/west, you will have more or less sun available to you for use as power. The other primary factor is how much shade your home receives.

Garrison said that it is best to contact a business such as his to do an assessment of your home. For example, Northeast Solar uses technology such as a Solar Pathfinder to measure how much sun your home would receive in a year, which in turn reveals how much power you could generate. They also use a Solmetric Sun-Eye to measure shade and solar access. “Once we have gathered all the information, we download it into a program that gives us a more accurate measure of electrical savings and output,” said Garrison.  DIY Resource:

How does the number of panels effect “payback?”

In general, for the average home (and 16 panels), it takes about six to eight years to payback the cost of installation, according to Garrison. In addition, some power companies allow you to contract to sell off excess power to be fed back into the general grid, saving you even more money over time.

The general cost of a 50-watt panel is about $215, or about $4.30 a watt. You also need to factor in installations costs. The average homeowner will pay between $4,000 and $5,000 to install an appropriate solar panel system.

If your home is especially shady and you aren’t willing to take down the surrounding trees, Garrison said it can take nearly double the time for payback. “Any shading on the roof reduces the amount of production,” Garrison said.

Keep in mind, most solar panel systems are estimated to last about 25 to 30 years.  Garrison said, “Gas, oil, and electric aren’t giving you a payback. Households using solar panels (for power) are able to stabilize long-term energy costs. You won’t be hit by the fluctuations in the energy market.”


A note about government incentives:

Currently, homeowners can take advantage of a variety of federal and state incentives, essentially paying back about 30 percent of the cost of the system on average.  However, Garrison warns that federal incentives are set to expire in 2016.

Cris Carl is a writer.  Read more articles like this one or get help with your home projects on

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