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Biofuels: A sober look at the potential

Biofuels: A sober look at the potential. Chris Field Carnegie Institution: Department of Global Ecology Stanford University, Department of Biology www.global-ecology.org. Bioenergy basics Bioenergy options Bioenergy potential. Why biofuels?. Climate protection Offset fossil fuels

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Biofuels: A sober look at the potential

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  1. Biofuels:A sober look at the potential Chris Field Carnegie Institution: Department of Global Ecology Stanford University, Department of Biology www.global-ecology.org • Bioenergy basics • Bioenergyoptions • Bioenergy potential

  2. Why biofuels? • Climate protection • Offset fossil fuels • Account for fossil fuels used to produce • Account for site carbon balance • Account for other greenhouse gases • Energy security • Local potential • Diversify sources

  3. How can biofuels be lower carbon? • Photosynthesis • Light + CO2 plant + O2 • Plant combustion • Plant + O2 energy + CO2 • Net • Light + CO2 energy + CO2

  4. How Biomass is Used for Energy In development Mature Semi-mature (Capital intensive ineficient)

  5. Carbon cycle basics • Fossil fuel + oxygen  carbon dioxide • Coal: C + O2 CO2 • Oil: C8H16 + 12O2  8CO2 + 8H2O • Natural Gas: CH4 + 3O2  CO2 + 2H2O • How much CO2? • Burning 1 lb of coal produces 3.6 lb of CO2 • Burning 1 gal of gas produces 18 lb of CO2 • The average person produces 30 lb CO2/day • The average American produces 170 lb CO2/day

  6. Setting the scale • Food for 1 person for one year • ~ 250 kg corn • = ethanol for one fill-up • ~ 80 l (20 gal) • At 25 mpg and 10,000 miles/y • The corn required to fuel one car on corn ethanol • Would feed 25 people

  7. 1 ZJ KT impact 12 ·1015 J supertanker 1011 J car/yr 450 EJ world energy consump/yr 100 J action 4 ·1022 J World fossil Fuel reserves 1013 J 1 gram E = Mc2 10 MJ 2400 kcal human/day 1 MJ 240 kcal 5 ZJ Solar energy On Earth in 1 year 1017 J biggest nuclear bomb 1 kg matter 4 GJ =ton TNT 6 GJ = barrel crude oil 0.5 MJ speeding car BTU QUAD 1 J 1 kJ 1 MJ 1 GJ 1 TJ 1 PJ 1 EJ 1 YJ 1 ZJ Energy Powers of ten 0 3 6 9 12 15 18 21 24

  8. Today, the world consumes 20X as much energy as in 1900!

  9. Future energy needs:Many times current

  10. Global annual plant growth • ~57 x 109 ton C on land • ~57 x 109 ton C in the oceans = 2500 EJ or 5 x global primary energy = 2500 EJ or 5 x global primary energy

  11. Energy in ag and pastures? Global Primary Energy = 450 EJ/y * In ½ biomass (to allow for roots), assume 45% C

  12. Will yields increase dramatically? • Historical trends – a century of success • 1-2%/y for major crops • Will this continue? • Can it accelerate?

  13. Ag yields – a century of successincreases of 1-2% y-1 Lobell and Field ERL 2007

  14. Limiting factors for global NPP Baldocchi et al. 2004 SCOPE 62

  15. Potential yield • Ag in relation to natural NPP • Ag/NPP -- Globally about 65% • Global average crop yields unlikely to exceed natural NPP for at least the next several decades

  16. Burn or Ferment? • If you want energy • Burn • If you want oil independence • Liquid biofuels • Battery technology

  17. Net energy balance ratio(biomass energy out/fossil energy in) • Corn ethanol ~1.2 • Sugarcane ethanol ~ 8 • Soy biodiesel ~ 2 • Palm biodiesel ~ 9 • Cellulosic ~5(?)

  18. Hill et al PNAS 2006

  19. Is sugarcane the answer? • High yields in warm, wet climates • Limited need for fossil energy • Burn bagasse for processing energy

  20. Fargione et al. Science 2008

  21. Is cellulosic the answer? Yield of 26.5 tons/acre in limited area test plots Courtesy of Steve Long et al

  22. Lignin occludes polysaccharides Cellulose Hemicellulose Lignin

  23. Lignin Effect of lignin content on enzymatic recovery of sugars from Miscanthus cellulose Hemi cellulose Switchgrass composition D Vrije et al (2002) Int J Hydrogen Energy 27,1381

  24. Biofuels and food USDA Amber Waves 2007

  25. Ethanol production cost per tonCO2 equivalent emissions offset(not accounting for land use) Thow & Warhurst, 2007 (divide by 2.2 for break even oil price in $/bbl)

  26. Food – the perfect storm? • Population • Food preferences • Climate change • Biofuels

  27. Bioenergy – the climate protective domain • Increase growth • Increase efficiency of conversion to useful products • Utilize sites where C loss from conversion is small in relation to bioenergy yield • Utilize sites that are not needed for something else

  28. Field, Campbell, Lobell TREE 2008

  29. Field, Campbell, Lobell TREE 2008

  30. Potential from abandoned land Field, Campbell, Lobell TREE 2008

  31. From available abandoned land 0.8 Pg C x 2 g Plant/g C x 0.5 g top/g plant x 16 EJ/Pg = 13 EJ = 3% of current global energy system

  32. Bioenergy • Climate impact depends on pre-existing ecosystem • Indirect as well as direct paths to carbon loss • Natural NPP reasonable proxy for potential yield under ag management • Available land resource limited • Quantity and quality • Big potential in absolute terms • But a small slice of present or future demand

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