Overview of Biofuels:
System Approach and Analysis
Prof. Steven G. Buckley
MAE 118b
February 21, 2007
(Slides 14-23 from presentation by Melanie Zauscher)
Taking a systems approach to biofuels
Biofuels in perspective
• Total world power draw ≈ 15 TW
• Total world solar flux ≈ 120,000 TW
So this should be easy, right?
Earth intercepts 8000 times more power than we use.
Going green – the reality
• 29.2% of earth is land
• 18.8% of the land is arable (CIA World Factbook)
• Photosynthesis is ~ 6% efficient at best, 1% is
reasonable average given ground coverage, etc.
So far: 8000 * 0.292 * 0.188 * 0.01  we still have 4.3
times as much energy as we consume!
(but this is if we take 100% of the arable land)
“Problem” of food production
• 11% of land area is in cropland (Worldwatch)
• Assuming this is all “arable land”  7.8% of land
remains
• 23% of land area is in pastureland (assume that much
of this is “non-arable,” but some of this is arable)
Sobering fact:
• 1960, 0.5 hectare of cropland per person, considered
adequate for healthy diverse omnivorous diet
• 2000, 0.23 hectare of cropland per person
– Declining quality and quantity
Conversion efficiency to fuel
• Energy stored in plants is recovered at what rate?
– Direct combustion – best biomass combustion plant
efficiency ≈ 20% conversion into electricity
– Production of biofuel – this is an open question!
• Currently ~ 10 billion gallons of both ethanol and ~ 1
billion gallons of biodiesel are produced annually,
worldwide (various sources)
– Gasoline consumption, worldwide ≈ 300 billion gallons
– Diesel consumption, worldwide ≈ ?
• 30 billion gallons of diesel in the U.S., annually
From Wikipedia / biodiesel, reference: http://www.globalpetroleumclub.com/
Biodiesel yield for some common crops
Crop
kg oil/ha
litres oil/ha
lbs oil/acre
US gal/acre
corn (maize)
145
172
129
18
oats
183
217
163
23
cotton
273
325
244
35
hemp
305
363
272
39
soybean
375
446
335
48
rice
696
828
622
88
cocoa (cacao)
863
1026
771
110
peanuts
890
1059
795
113
macadamia nuts
1887
2246
1685
240
Brazil nuts
2010
2392
1795
255
avocado
2217
2638
1980
282
coconut
2260
2689
2018
287
oil palm
5000
5950
4465
635
Algae
79832
95,000
10,000
Questions to ask
• What are the resource inputs?
– Fertilizer, pesticides
– Transportation
– Harvesting
– Processing
• What is being displaced / used?
– Food crops
– Water
– Forest, other land uses
As always, defining system boundaries is crucial!
• Example: how do you define the energy return on
energy invested for biofuels?
– DOE, 2006:
• Corn-based ethanol – 1.36 today
• Biodiesel – 3.2 today
– Institute for Local Self-Reliance
• Best corn-based ethanol – 2.09
• Best cellulosic bioethanol – 2.62
• Biggest academic critics: Prof. David Pimentel
(Cornell), Prof. Tad Patzak (U.C. Berkeley)
Critics point to flaws in analyses of biofuel energy
balances and “net carbon” efficiency
• Most fertilizers (e.g. urea, CO(NH2)2 have a common
ammonia (NH3) feedstock
– Tremendous amounts of energy are used in fertilizer
manufacture
– Some amount of this potent greenhouse gas escapes
during manufacture, and nitrogenous fertilizers convert
to greenhouse gases  converting into more
greenhouse gas equivalents than simply burning an
equivalent energy content of gasoline
Reading …
• H. Shapouri et al. “THE 2001 NET ENERGY
BALANCE OF CORN-ETHANOL”
– www.ethanolrfa.org/objects/pdf/net_energy_balance_20
04.pdf
• David Pimentel and Tad Patzek, "Ethanol Production
Using Corn, Switchgrass and Wood", Natural
Resources Research (March 2005), pp 65-76
– http://petroleum.berkeley.edu/papers/Biofuels/NRRetha
nol.2005.pdf
Conclusion: this is a close call!
Why bother with biofuels?
• Critical need for liquid transportation fuels
– Peak oil
– Geopolitics
– Climate change threat
Ethanol and Biodiesel are oxygenated fuels
derived from plant sources
• Oxygen on-board the fuel molecule
– Reduces incomplete combustion
• Promotes CO  CO2 and oxidation of soot particles
– The bonded O does not add to thermodynamic energy
content
• Less energy per unit mass or unit volume of fuel
• Production processes are plant-specific
Gallons of Gasoline Equivalents
Fuel
Unit of Measurement
Gasoline -regular
Gallon
Gasoline -reformulated
Gallon
Diesel #2
Gallon
Biodiesel -B20
Gallon
Biodiesel -B100
Gallon
Liquefied Petroleum Gas
Gallon
Ethanol -E85
Gallon
Ethanol -E100
Gallon
Liquefied Natural Gas
Gallon
Methanol -M85
Gallon
Methanol -M100
Gallon
Electricity
Kwh
Compressed Natural Gas
Ft3
Btu/Unit
114,100
112,000
129,800
127,840
120,000
84,300
81,800
76,100
75,000
65,400
56,800
3,400
900
GGE
1.00
1.02
0.88
0.89
0.95
1.35
1.39
1.50
1.52
1.74
2.01
33.56
126.78
http://www.nafa.org/Content/NavigationMenu/Resource_Center/Alternative_Fuels/
Energy_Equivalents/Energy_Equivalents.htm
Biodiesel
Made from vegetable oil or
animal fat and methanol or
ethanol
Locally produced, renewable,
simple to make and use
Can use same infrastructure as
petrodiesel including
engines
Sold as B2, B5, B20, B99 &
B100
Trans-esterification Reaction
This is most common way to reduce oil viscosity
Biodiesel Production Facilities
From the National Biodiesel
Board
Biodiesel Retailers
From the National Biodiesel
Board
Issues with Biodiesel
• Material compatibility:
– Biodiesel can dissolve neoprene rubber hoses and o-rings in
fuel lines of older vehicles
– Same problem with ULSD, so new cars are compatible
already
• Cold temperature problem
– Tendency to cloud and stop flowing in cold climates
Fuel
Diesel #2 Soydiesel
Cloud Point (oF)
-6
20
Shelf life
– No more than 6 months
Pahl 2005
Ethanol
Made from sugar, starch
or biomass
Locally produced,
renewable
Can use limited gasoline
infrastructure, and only
small blends on most
gasoline engines
Sold as octane enhancer,
E10, E25, E85 and
E100
Issues with Ethanol
• Can't transport it in pipelines
– Absorbs water
– More expensive to ship
• As E-85, has reduced MPG, so fuel costs more even
when ethanol is cheaper than gasoline
• Hard to find E-85
– A 2002 DOT/DOE study found ~1% of all flex-fuel cars
use E-85, but automakers still get credit for CAFE
standards
http://www.nhtsa.dot.gov/cars/rules/rulings/CAFE/alternativefuels/analysis.htm
Ethanol in California
• Current annual demand of ethanol is estimated ~950
million gallons
• Demand about ¼ of national supply
• Demand mostly to replace MTBE with (5.7%) ethanol
• Current CA annual production is ~25 million gallons
• 95% of ethanol delivered to CA is transported via rail cars
• ~1 million barrels of foreign ethanol were imported in 20042005
Perez 2005
Only one public ethanol (E-85) station in
California and that is in San Diego!
What is the future of biofuels?
• Not only are we carbon-constrained, we are landconstrained!
• How does peak oil influence the problem?
• Is the energy balance > 1 or < 1?
• Please read the Pimentel and Patzek paper for Friday
– http://petroleum.berkeley.edu/papers/Biofuels/NRRetha
nol.2005.pdf