Efficiency of biofuels

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.

Wikipedia ref:

As an example of varying numbers, a search of the USDOE website and Wikipedia gives the following results:

Energy Yield   Ethanol from corn
0.7 Cornell Uni - D Pinmental 2003
1.3 USDOE fact sheet
1.4 USDOE 2008 Energy Balance ..
1.67 USDOE report 2003
2.3 UDSOE report

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.

USDoE   2008 Energy Balance for the Corn-Ethanol Industry

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.

"It is on the record that Manildra has given more than half a million dollars to the government in the last two years for which records are public."

Hansard 22382   5 Mar 2004   Bob Brown, Greens senator

Manildra political donations

Party donations

Logically, and morally, this issue is a mess.

A further problem is the competition between food or fuel.



Corn growing 12350 4.9
Corn transport 1399 0.6
Ethanol prodn. 30586 12.1
Ethanol distribution. 1467 0.6
Total Energy used 45802 18.1
Energy in ethanol 76000 30.0
Profit 30198 11.9
Profit 40% 40%

US Dept of Energy 2001 - Energy balance



1 unit of energy

energy in ethanol produced

Incl. by-products
Sugar cane 2  
Corn 0.7 1.67
Switch grass 5.4  
Cellulose 7  
Miscanthus 7

Biomass-to-Wheel Efficiency 


BTW efficiency is a ratio of the kinetic energy of an automobile's wheels to the chemical energy of delivered biomass just before entering biorefineries.

Up to 13 scenarios were analyzed and compared to a base line case – corn ethanol/ICE. This analysis suggests that BEV, whose electricity is generated from stationary fuel cells, and SFCV, based on a hydrogen fuel cell vehicle with an on-board sugar-to-hydrogen bioreformer, would have the highest BTW efficiencies, nearly four times that of ethanol-ICE.....

...In the long term, a small fraction of the annual US biomass (e.g., 7.1%, or 700 million tons of biomass) would be sufficient to meet 100% of light-duty passenger vehicle fuel needs (i.e., 150 billion gallons of gasoline/ethanol per year),





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.



Energy Efficiency Analysis: Biomass-to-Wheel Efficiency Related with Biofuels Production, Fuel Distribution, andPowertrain Systems - 

Wei-Dong Huang1,2, Y-H Percival Zhang1,3,4,5


Internal combustion engine Ethanol  corn 7
Hybrid diesel with battery Ethyl ester Cellulose 13
Hybrid with battery Ethanol  Cellulose 15
Hybrid with battery Butanol Cellulose 15
Hybrid with battery Methanol Biomass 17
Hybrid diesel with battery FT-Diesel * CO + H2 18
Hybrid with battery Methane Biomass 19
Hybrid diesel with battery Di Methyl Ether Cellulose 19
Fuel Cell Methanol Biomass 19
Battery charged from mains Stationary boiler Biomass 20
Fuel Cell Hydrogen Biomass 22
Battery charged from mains GICC ** Biomass  25
Fuel Cell Sugar converted on board to H2 Cellulose 27
Battery charged from mains Stationary fuel cell Biomass 28

*  Diesel made from CO and H2by Fishcher-Tropsh process

Fishcher-Tropsh process  
**  Gasification Integrated Combined Cycle    

Fuels from biomass

A great variety of biofuels can be produced from lignocellulose biomass, including cellulosic ethanol[10][16], butanol and/or long chain alcohols [17][18], electricity [19][20], bioalkanes [21], fatty acid esters [6][22][23], hydrogen [24][25][26][27], hydrocarbons [28][29], and waxes [22].

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

Ethanol combustion in an internal combustion engine yields many of the products of incomplete combustion produced by gasoline and significantly larger amounts of formaldehyde and related species such as acetaldehyde. This leads to a significantly larger photochemical reactivity that generates much more ground level ozone. These data have been assembled into The Clean Fuels Report comparison of fuel emissions and show that ethanol exhaust generates 2.14 times as much ozone as does gasoline exhaust. When this is added into the custom Localised Pollution Index (LPI) of The Clean Fuels Report the local pollution (pollution that contributes to smog) is 1.7 on a scale where gasoline is 1.0 and higher numbers signify greater pollution. The California Air Resources Board formalized this issue in 2008 by recognizing control standards for formaldehydes as an emissions control group, much like the conventional NOx and Reactive Organic Gases (ROGs). Wikipedia