We can get the average on the horizontal area 12 cal/min cm2*47%=164 W/m2 This is the average value for a 24 hour day The average for an 8-hour day centered about noon is much larger. An optimistic but still reasonable estimate could be about 600W/m2 which is about 1520 Btw/ft2 Let's estimate the gross amount of solar energy incident on the US in a year. (The area of US is 3.615X 106 mile 2) The total is 5.6X1019 Btu/year. which is about 600 times the total energy consumed in US in1996(938X10 Btu) 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan UniversityWe can get the average on the horizontal area : ½ cal/min∙cm2 * 47% = 164 W/m2 This is the average value for a 24 hour day. The average for an 8-hour day centered about noon is much larger. An optimistic, but still reasonable, estimate could be about 600W/m2, which is about 1520 Btu/ft2. Let’s estimate the gross amount of solar energy incident on the US in a year. (The area of US is 3.615×106 mile2) The total is 5.6×1019 Btu/year, which is about 600 times the total energy consumed in US in1996 (93.8×1015 Btu)