Solar Cells - What if they were 100% efficient? Output amount?

Question

Can you give me an idea on how much energy from sunlight is received in a square foot area on earth. I've heard that solar cells are very inefficient loosing most energy to heat. I want to know how much energy could be extracted if it were 100% efficient. So using all solar cells within the US and the current energy output, if theye were 100% effificent how much energy would they now produce. Can u translate the output value into # of homes (or equivalent) per year so that i can understand.

Tx

Answer 1

I remember 1kW/sq m, so that would be about 100W/sq. ft.  Homes seem to average about 1kW per person.