How to Size PV Solar Panels

Due to rising energy costs and environmental concerns, investing in renewable energy sources such as wind and solar power makes sense financially as well as in terms of planetary health. If you're considering installing photovoltaic solar panels for your home, one of the first steps you need to take is determining the size of the array that you need to properly power your home. Installing an array that is too small to fit your energy needs means that you must continue to draw electricity from your local utility.

Calculator
Tape measure

Instructions

- 1
  Calculate the total Watt-hours per day for each appliance in your home. To do this, multiply the watts that the appliance uses by the number of hours it is used each day. (See Resources for a sample chart of appliance watt-usage.)
- 2
  Add the total Watt-hours for each appliance together to calculate your home's needed energy supply per day.
- 3
  Multiply the total number of daily Watt-hours you need by 1.3. This accounts for the energy that gets lost in the system.
- 4
  Measure the dimensions of the area (often the roof) where you are planning to install the solar panels. If the area measures 15 feet by 30 feet, the surface area is 450 square feet.
- 5
  Calculate the size of the solar array that you need. Photovoltaic solar panels generate 8 to 10 watts of power for every square foot of area, and provides output for about 5 hours per day. Multiply the wattage by the square footage of the planned array, using 8 watts on the low end and 10 watts on the high end.
  
  8 watts X 450 square feet = 3,600 watts
  
  10 watts X 450 square feet = 4,500 watts
- 6
  Subtract the output for both 8 watts (3,600) and 10 watts (4,500) from your home's daily required energy needs to determine if the array is large enough to meet your needs.

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