For a project that I was working on at home, I wanted to compute the solar radiation at a certain spot on the earth. This amount of energy is going to be a lesser number than 1366 Watts/meter^2. This is the total about of energy that has been measured by satelites above the earth. I found this website put up by NASA that helps to compute the energy with the input parameters of longitude, latitude, year, month. The output is sunrise, sunset, average daily sunlight and zenith angle (weighted cosine). What I would like is the number of hours that you could get solar energy. So to compute that here is what you do:
Compute insolation at specific location