ASTR 209 Lecture Notes - Eugenius Warming, Ernest Rutherford, Henri Becquerel
25 Jan 2013
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Lecture 3 (sat oct 2)continued previously: the sun"s luminosity (the number of energy-units the sun radiates each second) To calculate the sun"s luminosity, we needed to know the number of solar energy-units hitting a one-square-meter solar cell at the earth"s distance from the sun. One such plant produces energy at the rate of about 1 gw (1 gigawatt, or 109 watts or 109 joules/second). About 1400 j hits a one-square-meter solar cell above the atmosphere each second. The atmosphere reflects about 1/3 of the incident energy, so only about 1000 w reaches each square meter of solar cell on earth"s surface. A solar cell for producing electricity is not 100 % efficient (102%), and 1% (100%) might intuitively seem too low. A representative efficiency is between no (zero) factors of 10m and 2 factors of 10; use an efficiency of 101, or just 10%
