How to calculate how much PV you need to cover your electrical needs

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  1. Safety first.
  2. Determine your energy use - you can do this by collecting a year's worth of electric bills and adding up the energy (measured in kilo watt hours kW-hrs) used. Another way to do this is to do a plug load analysis of all of your electric devices.
  3. Determine the solar insolation in your region and more specifically location of the pv panel to determine kW-hrs/kW installed of PV. This is done with your latitude or distance from the equator.
  4. Divide your energy use by the available solar insolation found from step 3 to get your number of maximum installed Watts.
  5. Design a pv system that meets your electrical power needs given the parameters of the available insolation. Keep in mind that solar insolation varies seasonally and daily.


  1. Lets say you are average. The average annual electricity use per household is 10,654 kW-hrs/year (Energy Information Administration, 2005).
  2. From the solar resource map go here or here. If we assume you live in Kingston you can expect at least 1200 kW-hrs/kW (more if you are using thin film PV).
  3. 10,654/1200 = 8.9 kW. This is actually a pretty big system -- which shows you just how wasteful most people are with energy.


Before you consider installing any type of photovoltaic you should first work to optimize your home's energy efficiency.

Things You will Need[edit]

For a plug load analysis you will need a watt meter.

Related How-Tos[edit]

Sources and Citations[edit]

Energy Information Administration (EIA). 2005. U.S. Household Electricity Report. Release date: July 14, 2005 at [1]