Efficiency of biofuels
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Energy profit of ethanol from corn
The greatest problem with ethanol is that it takes energy to make it. Do we make a profit in terms of energy used vs energy produced? We'll refer to it as energy yield. 1.0 means no net gain, 2.0 means 1 unit of energy has produced product with 2 units of energy.
It is very difficult to get a consistent view on this. The results are often driven by commercial or political agenda.
Do you include the goods the workers consume? Do you give the by-products any share of the energy cost?
For example, counting the energy in the by-products changes an energy yield of 1.06 to 1.67.
As an example of varying numbers, a search of the USDOE website and Wikipedia gives the following results:
The results are inconsistent
The conclusion of the study summarised in the table on the right is a yield of 1.4 or profit of 40%
The report below concludes that for every unit of energy invested in producing ethanol from corn, 2.3 units are produced in the ethanol.
Different crops and different climates are very different so the numbers will vary accordingly.
There is a lot of political and commercial pressure to show that ethanol has more energy than is required to produce it. and there are reports proving it.
However some say if you include everything such as food for the workers, and packaging etc for their goods, and so on, that more energy is used than the ethanol can release.
Cornell ecologist's study finds that producing ethanol and biodiesel from corn and other crops is not worth the energy. However this study has been criticised widely for assuming all crops are irrigated, and allocating none of the energy costs to the by-products. There are claims the author has an agenda.
It should be pointed out that Manildra, Australia's main ethanol producer, is one of the largest political donors in Australia.
Hansard 22382 5 Mar 2004 Bob Brown, Greens senator
Logically, and morally, this issue is a mess.
A further problem is the competition between food or fuel.
US Dept of Energy 2001 - Energy balance
The paper looks at the total energy used to grow, process, distribute, and convert the energy to motion.
The most efficient system is to the battery electric vehicle charged from stationary fuel cells. Followed by a sugar fuelled fuel cell vehicle with an on board bioreactor converting the sugar to hydrogen to be used in the fuel cell.
Ethanol from corn was the least efficient.
This analysis is made up of several stages listed below.
Wei-Dong Huang1,2, Y-H Percival Zhang1,3,4,5
Fuels from biomass
A great variety of biofuels can be produced from lignocellulose biomass, including cellulosic ethanol, , butanol and/or long chain alcohols , , electricity , , bioalkanes , fatty acid esters , , , hydrogen , , , , hydrocarbons , , and waxes .
Biomass to wheels efficiency is a ratio of the kinetic energy of an automobile's wheels to the chemical energy of delivered biomass just before entering biorefineries
The different possibilities
This diagram shows the fuel options looked at in this study.
Apart from the first item it assumes all sugar is from cellulose.
The study does not look at sugar from cane, palm, beet, or agave. Nor does it look at oil from plants.
Key to abbreviations
ICE Internal Combustion Vehicle
HEV Hybrid Electric Vehicle
SFCV Sugar Fuel Cell Vehicle - sugar converted to H2 on board
FC Fuel cell
FCV Hydrogen Fuel cell vehicle
BEV Battery Electric Vehicle
BIGCC - Biomass converted to syngas, then burned in a gas turbine, then the exhaust gases producing steam for a steam turbine.
Syngas is synthesis gas, a mixture of CO and H2 formed by partially burning biomass or fossil fuel. Using the Fischer-Tropsh process it can be converted to diesel and otehr hydrocarbons.(FT-Diesel)
Efficiency of fuel production
Efficiency of distribution of energy
Fuel to wheel efficiency
gas = gasoline
ICE - Internal Combustion Vehicle
HEV - Hybrid Electric Vehicle
FCV - Hydrogen Fuel cell vehicle
SFCV - Sugar Fuel Cell Vehicle
BEV - Battery Electric Vehicle BEV
Biomass to Wheel efficiency BTW
(gas seems to refer to gasoline (petrol) not gas-methane)
Only 7% of the chemical energy in corn kernels is converted to the kinetic energy on wheels.
An ethanol gasoline Hybrid Electric Vehicle (HEV-gas) system would double values to 14–18%.
There is no significant difference in between butanol and ethanol, but butanol may have other important future applications, such as powering jet planes.
The values of methane/HEV-gas and methanol/HEV-gas are 19% and 17%.
ICE-diesel has higher efficiencies than gasoline internal Combustion Engine (ICE-gas) so diesel hybrids has been assessed.
For ester-diesel, a significant amount of energy is lost during aerobic fermentation, resulting in low values.
Even for the niche jet fuels market, the production of ester-diesel through semi-aerobic microbial fermentation might not be competitive with anaerobic butanol fermentation.
Although (hydrogen) fuel cell vehicles (FCVs) have high efficiencies, energy loss in hydrogen distribution discounts FCV's advantages over HEV-diesel.
The sugar Fuel Cell Vehicle SFCV scenario would have very high values of approximately 27% due to lower energy consumption in fuel transport and heat recapture in the sugar-to-hydrogen biotransformation, compared to the H2/FCV scenario.
Battery Electric Vehicles BEV scenarios are among the highest values, from 20% to 28%.
Air quality from ethanol fuels