As I recall, the "solar constant" (amount of energy hitting a unit area directly facing the sun) at the orbit of the earth from the sun (i.e., outside of the atmosphere) is about 1400 W/meter^2. This is what would be available to a satellite with a collecting panel facing directly at the sun. A fair amount of this energy is absorbed by the atmosphere, dropping it to levels around 200 W/m^2 in the northern latitudes, and around 900 W/m^2 near the equator on a sunny day when the sun is directly overhead.
Note that the light from the sun has to travel thru lots more atmosphere at the high northern and southern latitudes than at the equator. Note also that amount of energy that crosses any given area drops off as the cosine of the angle of the sun from the vertical. The second of these effects can be eliminated by "sun tracking" in the solar array. But for stationary arrays (tops of buildings, etc.), both of these effects seriously degrade the amount of energy used, as does cloud cover.
I hope you find this info useful.
I'm going to include this in a note that I post to the original comments for anyone else who wonders about it.
ciao.
Slashdot Mirror
As I recall, the "solar constant" (amount of energy hitting a unit area directly facing the sun) at the orbit of the earth from the sun (i.e., outside of the atmosphere) is about 1400 W/meter^2. This is what would be available to a satellite with a collecting panel facing directly at the sun. A fair amount of this energy is absorbed by the atmosphere, dropping it to levels around 200 W/m^2 in the northern latitudes, and around 900 W/m^2 near the equator on a sunny day when the sun is directly overhead. Note that the light from the sun has to travel thru lots more atmosphere at the high northern and southern latitudes than at the equator. Note also that amount of energy that crosses any given area drops off as the cosine of the angle of the sun from the vertical. The second of these effects can be eliminated by "sun tracking" in the solar array. But for stationary arrays (tops of buildings, etc.), both of these effects seriously degrade the amount of energy used, as does cloud cover. I hope you find this info useful. I'm going to include this in a note that I post to the original comments for anyone else who wonders about it. ciao.