How to Determine How Much Solar Energy Can Be Generated

Determine the total surface area available to collect sunlight. Generally this means just the surface area of all the solar panels in a project, but it also includes mirrors or other reflectors if these are used to concentrate sunlight onto a smaller area.

Divide the total surface area in square feet by 10 to get the gross maximum insolation in kilowatts.

Find the average overall angle at which the sun's rays normally strike the collection surface. Bear in mind that the sun moves across the sky over the course of a day, and the angle will change unless your solar panels are mounted on gimbals to track the sun's position. Also remember that the sun's path will change with the seasons.

Multiply the gross maximum insolation in kilowatts by the sine of the angle. This will give you the adjusted insolation.

Find the efficiency rating of the solar cells in the array. Most of the light that hits a photovoltaic cell does something other than generate voltage. Much of it is reflected away, and some is absorbed as heat, and so typically solar panels only convert 14 percent to 19 percent of the received light into electricity.

Multiply the adjusted insolation by the solar cells' efficiency rating to get the base output. This is the basic amount of power the array should generate under optimal conditions.

Adjust for expected weather pattern and day length to figure out how many hours of sunlight the array will receive. Multiply the number of hours by the base output in kilowatts, and the result will be the expected energy generated as measured in kilowatt-hours.