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Comparing Photosynthesis and Photovoltaics |
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Photosynthesis |
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claim#1 |
2,400,000,000,000,000,000 |
btu/year |
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* |
0.293 |
watt-hrs/btu |
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= |
703,200,000,000,000,000 |
watt-hrs/year |
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/ |
150,000,000 |
km^2 of land on earth |
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= |
4,688,000,000 |
watt-hr/sq km |
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PV |
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claim |
1,000 |
watts/meter^2 at noon |
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* |
5 |
hrs/day of noon sun equivalent, global
average |
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= |
5,000 |
watt-hrs/m^2/day |
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* |
365 |
days/year |
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= |
1,825,000 |
watt-hrs/m^2/year |
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* |
1,000,000 |
m^2/km^2 |
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= |
1,825,000,000,000 |
watt-hrs/km^2/year |
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Ratio PV:Photosynthesis |
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389 |
PV:Biomass |
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0.26% |
Biomass:PV |
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Validate Claim |
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claim#1 |
2.4E+18 |
btu terrestrial plants |
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/ |
1.2E+11 |
tonnes |
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= |
20,000,000 |
btu/tonne |
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/ |
1,000 |
kg/tonne |
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/ |
2.2 |
kg/lb |
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= |
9,091 |
btu/lb |
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(This result meets sanity test.) |
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Claim#1: |
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Today, terrestrial
plants produce about 120 billion metric tons of biomass (dry weight)1 globally each year (IPCC,
2001). The energy in this biomass totals about 2,400 quads2 (1 quad = 1015 Btu).
Modern economies, however, rely extensively on fossil fuels rather than
biomass for their energy. In 2001, the world consumption of fossil fuels
totaled about 315 quads, about one-quarter of which was consumed in the
United States (BP, 2002). |
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http://www.nae.edu/nae/bridgecom.nsf/weblinks/MKUF-5NTMX9?OpenDocument |
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