16_energy

Hydrogen burns very cleanly producing little more

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Unformatted text preview: onds to 80 QBtu – comparable to 100 QBtu total consumption • the work is never done! • U.S. actually has wood-fired plants: 6,500 MW-worth – Iowa cornfield only 1.5% efficient: solar PV easily beats – in 1992, burned equivalent of 200,000 barrels of oil per day • Yet powerful lobbies have made sure this has a place at the table – Brazil works well on sugar cane: doesn’t mean corn is as good! Winter 2007 Lecture 16 83 Winter 2007 84 21 Energy, Sustainability 03/15/2007 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 Renewables list Renewables, continued Renewables, • Geothermal: run heat engines off earth’s internal heat earth’ • Solar (photovoltaic, solar thermal) (photovoltaic, – could be as much as 1.5 QBtu/yr w orldwide in 50 years – limited to a few rare sites – get 100 QBtu/yr with < 2% coverage of U.S. land area • Wind • Tidal: oscillating hydroelectric “dams” dams” – maybe 180 QBtu/yr worldwide, maybe 25 QBtu in U.S. – a few rare sites are conducive to this (Bay of Fundy, for example) – up to 1 QBtu/yr practical w orldwide • Hydroelectric – 70 QBtu/yr feasible worldwide: twice current development – 5 QBtu/yr max potential in U.S. • Ocean Thermal Energy Conversion (OTEC) – use thermal gradient to drive heat engine – complex, at sea, small power outputs Winter 2007 85 Winter 2007 86 UCSD: Physics 121; 2007 UCSD: Physics 121; 2007 The Hydrogen Solution Defeating the purpose? • If we could find pockets of hydrogen gas, this would be great, as hydrogen carries about 32 Calories/gram great through simple reaction: 2H2 + O2 – this is great for the environment 2H2O • But if the hydrogen is produced by fossil-fuelpowered plants, all this advantage is lost • Two big problems: – No natural pockets of hydrogen gas – Very bulky in gaseous form – coal puts out t ons of CO2, plus SO2, and other nasties – have to deal with plant efficiency (33%) times electrolysis efficiency (65%) times engine efficiency (optimistic 65% fuel cell??) = 14% – better off burning fossil fuel directly in your car, and getting 20% efficiency • 11,000 times l...
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This note was uploaded on 01/30/2014 for the course PHYS 121 taught by Professor Staff during the Winter '08 term at UCSD.

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