I have been trying to find some values for how much watts per square meter there is of energy on the ground due to the sun, but everywhere there are different values ranging from 100-1000 Watts so I have no clue of what to believe... And also are these values per second/minute/day??? So however due to all the uncertainties I really appreciate some help to find the answer for this one. Another thing I also wish to know is how large area of solar cells (let's say they can absorb all the energy that hits them) is required to power the whole north America for a year, also this question has been a struggle to find. I'm also aware of energy loss due to the atmosphere, clouds and such. Thanks in advance, Robin.