Question

Using the solar constant(approx 1.361kW/m^2) estimate the rate at which the whole Earth receives energy from the Sun

Answer 1

Earth is a sphere so that its surface area = 4pi r^2.
and Sun will hit only half its area at a time so cross sectional area =2pi r^2.
rate = E/A
thus Energy = rate *A

Answer 2

but the answer given was 1.73e17 which is he result of solar constant*pi r^2
similar question here https://answers.yahoo.com/question/index?qid=20091108092559AAbV0tM

Answer 3

Yea that is right as rate should be parallel to the direction of area ,so it would be the cross sectional area which is pi r^2 or 2pi r^2 (dot product with the rate).