Intensity of sunlight at the earth’s orbit
At the earth’s distance from the sun
(93 million miles = 1.5 x 1011m),
the intensity of sunlight we receive is about
I = P/A = (4 x 1026Watts)/(4*?*[1.5x1011m]2) ? 1600 W/m2.
However, due to reflection off the atmosphere and due to day/night and slanting angle of sunlight during the day, the average intensity striking the earth is only about 250 W/m2.