Biofuels: A sober look at the potential

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BiofuelsA 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

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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

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How can biofuels be lower carbon?

• Photosynthesis
• Light CO2 plant O2
• Plant combustion
• Plant O2 energy CO2
• Net
• Light CO2 energy CO2

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

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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

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QUAD
BTU
1 kJ
1 MJ
1 GJ
1 TJ
1 PJ
1 EJ
1 YJ
1 ZJ
1 J
Energy
Powers of ten
0
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Today, the world consumes 20X as much energy as
in 1900!
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Future energy needsMany times current
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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
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Energy in ag and pastures?
Global Primary Energy 450 EJ/y In ½
biomass (to allow for roots), assume 45 C
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Will yields increase dramatically?

• Historical trends a century of success
• 1-2/y for major crops
• Will this continue?
• Can it accelerate?

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Ag yields a century of successincreases of
1-2 y-1
Lobell and Field ERL 2007
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Limiting factors for global NPP
Baldocchi et al. 2004 SCOPE 62
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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

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Burn or Ferment?

• If you want energy
• Burn
• If you want oil independence
• Liquid biofuels
• Battery technology

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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(?)

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Hill et al PNAS 2006
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Is sugarcane the answer?

• High yields in warm, wet climates
• Limited need for fossil energy
• Burn bagasse for processing energy

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Fargione et al. Science 2008
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Is cellulosic the answer?
Yield of 26.5 tons/acre in limited area test plots
Courtesy of Steve Long et al
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Lignin occludes polysaccharides
Cellulose
Hemicellulose
Lignin
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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
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Biofuels and food
USDA Amber Waves 2007
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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)
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Food the perfect storm?

• Population
• Food preferences
• Climate change
• Biofuels

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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

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