Confirm the size and number of solar panels you have. You will need the have the area in terms of square feet or meters.
Find the average amount of radiation that will fall on your location per year. Use an online chart to determine this amount. You may also find the information from local government sources. A typical level of radiation is 180 Watts per meter squared.
Use a loss factor based on the efficiency of your panels. Due to current levels of technology, this loss is substantial and can be around 80%.
Divide the radiation by 1,000 to simplify and then multiply by the loss factor to determine the capacity factor.
Capacity Factor = (180/1000) * .8 = .144
Multiply the capacity factor by 100 million to find the value in terms of Mega Watts (MW), a unit of million(s) of Watts.
.144 * 100 million Watts = 14.4 MW (or 14,400,000 Watts) of power per meter squared annually.