At what altitude does a solar panel see a noticeable increase in wattage/cubic meter if it is lifted into the air? I understand the maximum is a bit over 1 kilowatt/meter2 at sea level (not actually converted to usable energy, this is much less and depends on the technology) but that this amount obviously increases as an object reaches the exosphere and beyond. Would there be a noticeable increase at say, 12km or at the top of the thermosphere? I found one useful site: http://www.pages.drexel.edu/~brooksdr/DRB_web_page/papers/UsingTheSun/using.htm but it is talking mainly theoretical. Does anyone know of studies that have been done to look at real life w/m^2 at various levels of elevation? Thanks.