Survey of Energy Resources 2007 Solar energy is the most
abundant permanent energy resource on earth and it is available
for use in its direct (solar radiation) and indirect (wind,
biomass, hydro, ocean etc.) forms. This commentary is limited to
the direct use of solar radiation, the earth's prime energy
resource. The Sun emits energy at a rate of 3.8x1023 kW. Of this
total, only a tiny fraction, approximately 1.8x1014 kW is
intercepted by the earth, which is located about 150 million km
from the sun. About 60% of this amount or 1.08x1014 reaches the
surface of the earth. The rest is reflected back into space and
absorbed by the atmosphere. Even if only 0.1% of this energy
could be converted at an efficiency of only 10% it would be four
times the world's total generating capacity of about 3 000 GW.
Looking at it another way, the total annual solar radiation
falling on the earth is more than 7 500 times the world's total
annual primary energy consumption of 450 EJ. The annual solar
radiation reaching the earth