MIT22_081JF10_lec19a

MIT22_081JF10_lec19a - Biomass Part I: Resources and uses...

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Biomass Part I: Resources and uses William H. Green Sustainable Energy MIT November 16, 2010
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Sustainable Energy: Big Picture • People want electricity , transport , heat • Now use: coal oil gas • Major Challenges: –CO 2 to atmosphere : climate change un short on oil? ecurity, price –Run short on oil? Security, price Price : most people in the world can’t afford the energy they want
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Possible Solutions • CO 2 : switch from conventional coal – Efficiency: lighting, cooling? – Coal b gas combined cycle – Non-emitting power sources – CO2 underground sequestration urn Biomass instead of coal – Burn Biomass instead of coal • Oil running out : Efficiency, Alternatives – Vehicle efficiency, urban planning – Batteries or natural gas for land transport – Coal, tar, gas b synfuels with CO 2 sequestration – Biomass b liquid fuels • Price? – Can Biomass energy be cheap??
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History, overview of biomass • Largest historical energy source • Largest current renewable energy source • Many historical examples of resource depletion – England, Easter Island deforestation ahel desertification – Sahel desertification – Whale oil • Scalability and land use resources are a challenge • Possible better ways: – Waste from agriculture, forestry – Energy crops / algae on waste land
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Solar insolation • Solar “constant”: 1366 W/m 2 – Measured outside the earth’s atmosphere – Varies with seasons • On planet’s surface effected by geometry and filtering. • Photosynthetically active region (PAR): ~ 400-700 nm Photosynthesis ~ 1% efficient Energy stored <3 MW / (km) 2 arable land Maps of insolation at the top of the atmosphere and the Earth's surface removed due to copyright restrictions. Image by Robert A. Rohde / Global Warming Art.
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Biomass: The Source • Photosynthesis stores ~300 EJ/yr as biomass energy – Human energy use ~400 EJ/yr – Carbon cycle: plants die, decay to CO2 – In fertile areas ~ 10 -5 EJ/(km) 2 /yr • Requires ~250 kg H 2 O to grow 1 kg biomass arth’s total land surface ~10 m) – Earth’s total land surface ~10 8 (km) 2 • For large scale biomass energy NEED LOTS OF LAND (even much more than solar) and WATER • If you have spare land and fresh water, relatively inexpensive to grow and harvest (e.g. much less capital than solar!)
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What is biomass? Properties • Solid carbon-based fuel (like coal)
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MIT22_081JF10_lec19a - Biomass Part I: Resources and uses...

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