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

##  Steps

1. Determine your energy use - you can do this by collecting a year's worth of electric bills and adding up the energy (measured in kW-hrs) used. Another way to do this is to do a plug load analysis of all of your electric devices.
2. Determine the solar insolation in your region to determine kW-hrs/kW installed of PV.
3. Divide one by two to get your number of installed Watts.

##  Example

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.

##  Warnings

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

##  Things You will Need

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

##  Sources and Citations

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