A problem ...
|A recent article says that high-yield
tree farming can produce 9000
pounds of wood per year per acre.
Express that value in watts
per square meter.
|The solution||Nine thousand pounds is about 4100 kilograms; wood has a heat value of about 15 million joules per kilogram; one year is 31.6 million seconds; 1 acre is 4047 square meters. Therefore, this highly touted manifestation of solar energy produces about 60 billion joules per 31.6 million seconds (amounting to about 1950 watts) per 4047 square meters. That is, high-yield tree-farming results in about 0.5 watts per square meter. (Sunlight in the US averages 200 watts per square meter, of which the 0.5 figure is a paltry quarter of a percent.)|
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