Take the average solar flux reaching the US to be 200 W/m2. (This averages over

Question

Take the average solar flux reaching the US to be 200 W/m2. (This averages over a variety of conditions.)
a. Find the total energy produced in one year by a 1m2 cell producing energy with an efficiency of 15%.
b. How much area would be required to supply the US with all its electricity for a year, about 4.0 x 1012 kW*hr?
c. Real solar arrays need about 2.5 times larger area that value found in b to avoid showing of adjacent cells. What fraction of the US land area (9 x 106 km2) would have to be covered with solar cells to provide all of the energy required?

Explanation / Answer

a) In 1m² the power supply is:

P =(15%)(200) = 30 W

in one year the energy produced is:

E = Pt = (30(365)(24)(60)(60) =9.4608*10 J

b) Remember that:

1 kWhr = 3.6*10 J

The total area will be:

A = EUS/E = 4*10¹²(3.6*10)/(9.4608*10) = 1.522*10¹ m²

c) The area A is greater than the US land are.

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