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Virginia Tech professor proposes simple biomass-to-wheel efficiency analysis to inform decisions on biomass/biofuel/powertrain combinations; the advantage of sugar fuel cell vehicles

Comparison of biomass-to-wheel (BTW) efficiency for different biomass utilization scenarios. Sugar Fuel Cell Vehicles and BEVs charged with electricity from a fuel cell (green bars) were the most efficient. Huang and Zhang. Click to enlarge.

The potential role of biomass-derived fuels as a substitute for petroleum has engendered a great deal of research into different fuel pathways and possible powertrain combinations. Numerous life cycle analyses (LCAs) have attempted—and continue to—gauge the potential sustainability and impacts of these possible pairings.

However, notes Virginia Tech Prof. Y-H Percival Zhang in an open access paper published in the journal PLoS ONE, such analyses rely heavily on numerous assumptions, uncertain inputs (e.g., fertilizers, pesticides, farm machinery), energy conversion coefficients among different energy forms and sources, system boundaries, and so on. As a result, conflicting conclusions have been made even for well-known corn ethanol biorefineries, he points out. Zhang proposes using a simple biomass-to-wheel (BTW) energy efficiency analysis to help make a more informed decision for how to utilize (limited) biomass resources more efficiently.

The BTW efficiency (ηBTW) analysis methodology involves three elements: biomass-to-fuel (BTF), fuel distribution, and fuel-to-wheel (FTW). 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.

The scheme of energy efficiency analysis for the biomass-to-wheel efficiency (ηBTW) calculation.
  • W is the kinetic energy transferred to wheels;
  • EB is the chemical combustion energy of the biomass, where dry corn stover as a typical biomass contains ~65% carbohydrates (cellulose and hemicellulose, mainly); ~18% lignin; ~5% ash; ~12% other organic molecules; and the EB value is 16.5 MJ of low heating value/kg of corn stover;
  • ηBTF is the biomass-to-fuel (BTF) efficiency through biorefineries or power stations without significant inputs or outputs of other energy. ηBTF can be calculated as EF/EB, where EF is the fuel produced in biorefineries or power stations.
  • ηTDL is the fuel loss efficiency during its transport and distribution. ηTDL can be calculated as fuel consumed for its transport and distribution from biorefineries to vehicles [EC/(EC+ET)] where EC is the energy consumed in the process of fuel transport and distribution, ET is the fuel energy delivered to end users (i.e., powertrains), and EF = EC + ET.
  • ηFTW is the fuel-to-wheel (FTW) efficiency from the fuel to kinetic energy through powertrain. ηFTW can be calculated as a ratio between the kinetic energy on wheels (W) and fuel energy in the tank (ET).

Conducting this BTW analysis is simple and straightforward because it not only avoids uncertainties or debates for (i) biomass production-related issues, (ii) feedstock collection and transport, and (iii) land use change, but also excludes water consumption issues and greenhouse gas emissions in the whole biosystem. Therefore, energy efficiency analysis (but not life cycle analysis) may not only be helpful in narrowing down numerous choices before more complicated LCA and techno-economic analyses are conducted, but may also increase the transparency of such analyses.

—Huang and Zhang

Using this BTW method, Zhang and his colleague Wei-Dong Huang assessed combinations of different biomass-to-biofuel approaches and their respective powertrain systems and compared them to a baseline corn-ethanol-ICE.

They ran different scenarios of fuel production through sugar, syngas, and steam platforms as well as six different powertrains viz. internal combustion engine vehicle (ICE); hybrid electric vehicle-gasoline (HEV-gas); hybrid electric vehicle-diesel (HEV-diesel); (hydrogen) fuel cell vehicle (FCV); battery electric vehicle (BEV); and sugar fuel cell vehicle (SFCV).

The combination of 12 kinds of biofuel production approaches and 6 kinds of advanced powertrains for passenger vehicles results in more than 20 scenarios (shown in the figure below). In the current paper, they calculated 14 scenarios.

Scenarios of the production of fuels from biomass and their respective fuel power train systems. Solid lines represent the scenarios analyzed; the dotted lines represent possible scenarios not analyzed. Huang and Zhang. Click to enlarge.

Among the findings:

  • The current corn ethanol/ICE scenario has ηBTW value of ~7%—i.e., only 7% of the chemical energy in corn kernels is converted to the kinetic energy on wheels, implying a great potential in increasing biomass utilization efficiency.

  • An ethanol HEV-gas system would double ηBTW values to 14–18%, suggesting the importance of developing hybrid electric vehicles based on available liquid fuel distribution system.

  • There is no significant difference in ηBTW between butanol and ethanol, but butanol may have other important future applications, such as powering jet planes.

  • The ηBTW values of methane/HEV-gas and methanol/HEV-gas are 19% and 17%, respectively, higher than those of ethanol and butanol, mainly due to higher product yields.

  • For ester-diesel, a significant amount of energy is lost during aerobic fermentation due to thermodynamic and bioenergetic limits, resulting in low ηBTW values.

  • Although (hydrogen) fuel cell vehicles (FCVs) have higher ηFTW efficiencies than ICE-gas and ICE-diesel, the H2/FCV scenario shows ~46% and ~15% ηBTW enhancements over ethanol HEV-gas and DME HEV-diesel, respectively, because significant energy loss in hydrogen distribution discounts FCV’s advantages over HEV-diesel.

  • The sugar/SFCV scenario would have very high ηBTW 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.

  • BEV scenarios are among the highest ηBTW values, from 20% to 28%, with increasing electricity generation efficiencies from direct combustion, BIGCC, to FC-power.

Conducting energy efficiency analysis is simpler, faster, and less controversial than conducting life cycle analysis because the latter heavily depends on so many different assumptions and uncertain inputs. Here we present a straightforward energy efficiency analysis from biomass to wheels for different options, which contains three elements. Each element can be analyzed separately and adjusted individually; most of which have data well-documented in literature. Because of the same input and output in all cases, an increase in energy conversion efficiency nearly equals impact reductions in carbon and water footprints on the environment. Most of the results obtained from this biomass-to-wheel analysis were in good agreement with previous, more complicated life cycle analyses, supporting the validity of this methodology.

...Both the sugar/sugar fuel cell vehicle (SFCV) and fuel cell (FC)-power/ battery electric vehicle (BEV) scenarios would have [ηBTW values] nearly four times that of corn ethanol/ICE-gas, implying the importance of enhancing BTW efficiency in each conversion element.

—Huang and Zhang

The Sugar Fuel Cell Vehicle (SFCV). Zhang proposed the concept of the SFCV in a paper in the RSC journal Energy & Environmental Science in 2009 to address problems such as high-density hydrogen storage in FCV, low-cost sustainable hydrogen production, costly hydrogen distribution infrastructure, and safety. The SFCV concept uses renewable sugar (carbohydrate) as a high hydrogen density carrier (gravimetric density of 8.33% mass H2, volumetric density of >100 g H2 per liter).

Conceptual sugar-to-electricity system. Zhang 2009.
Click to enlarge.
  Conceptual hybrid power train system including on-board sugarto-hydrogen converter, PEM fuel cell and rechargeable battery. Zhang 2009. Click to enlarge.

Transportation and distribution of the sugar/water slurry or sugar slurry could easily use available infrastructure.

This hypothetical SFCV would contain a sugar tank and an on-board sugar-to-hydrogen bioreformer, with a combined sugar tank and bioreformer volume that is much smaller than a compressed hydrogen tank or other hydrogen storage approaches. The on-board biotransformer would convert the sugar solution to high-purity hydrogen and carbon dioxide using a stabilized enzyme cocktail and a small-size hydrogen storage container would serve as a buffer, balancing hydrogen production and consumption.

Feeding a mixture of CO2/H2 or pure hydrogen in the proton exchange membrane (PEM) fuel cells would decrease system complexity and greatly increase system operation performance, and the waste heat release from PEM fuel cells would be coupled to the heat needed by the bioreformer.

When extra kinetic energy is needed for acceleration or start-up, electrical energy stored in the rechargeable battery would be released, as in a hybrid electric vehicle. The on-board bioreformer in SFCVs, mediated by the thermoenzyme cocktails under modest reaction conditions may be capable of providing high-purity hydrogen at a rate of ~23.5 g H2/L/h or higher, Huang and Zhang say. Given a bioreformer size of 42.8 L, one kg of hydrogen per hour could then be produced to drive the PEM fuel cell stack.

High-speed biohydrogen production rates have been implemented by high cell-density microbial fermentation. It is widely known that enzymatic reactions usually are at least one order-of-magnitude faster than microbial fermentations because the former has no cellular membrane to slow down mass transfer and much higher biocatalyst loadings, without the dilution of other biomacromolecules (e.g., DNA, RNA, other cellular proteins)...We expect that enzyme deactivation in the biotransformer will be solved through infrequent service maintenance, similar to the oil/air filter change for gasoline/ ICE vehicles.

Several technical obstacles of SFCVs include poor enzyme stability, labile and costly coenzymes, low reaction rates, and complicated system configuration and control. A huge potential market (e.g., nearly one trillion of US dollars per year) provides the motivation to solve these issues within a short time. Current progress includes the discovery of thermostable enzymes from extremophiles and low-cost production of recombinant enzymes, engineering redox enzymes that can work on small-size biomimetic cofactors, and accelerating hydrogen generation rates.

—Huang and Zhang

Since, under the BTW analysis, the SFCV would have ~3.4 times the FTW efficiency (ηFTW) of ethanol/ICE-gas, one kg of sugar (i.e., 17 MG/kg) would release more kinetic energy than one kg of gasoline (i.e., 46.4 MJ/kg) from ICE-gas, Huang and Zhang said.

Assessment of any energy system is really challenging because it involves so many factors. Generally speaking, efficiency and cost are usually the two most important criteria. Since thermodynamics (energy efficiency) determine economics in the long term, SFCVs and FC-power/BEV seemed to be long-term winner candidates, but SFCVs have other important advantages. Currently and in the short term, costs mostly determine market acceptance and dominance.

But cost analysis is more complicated than energy efficiency analysis, because the former involves direct costs (e.g., fuel, vehicle, etc.), indirect costs (e.g., vehicle service, taxes, subsidies, infrastructure costs for repairing and rebuilding, resource availability, etc.), and hidden costs (e.g., safety, toxicity, waste treatment, greenhouse gas emissions, military expenditures, etc.). In the short term, cellulosic ethanol plus HEV-gas and methane-HEV-gas may be the most promising options.

—Huang and Zhang


  • Huang W-D, Zhang Y-HP (2011) Energy Efficiency Analysis: Biomass-to-Wheel Efficiency Related with Biofuels Production, Fuel Distribution, and Powertrain Systems. PLoS ONE 6(7): e22113 doi: 10.1371/journal.pone.0022113

  • Y.-H. Percival Zhang (2009) A sweet out-of-the-box solution to the hydrogen economy: is the sugar-powered car science fiction? Energy Environ. Sci., 2, 272-282 doi: 10.1039/B818694D

  • Zhang Y-HP, Evans BR, Mielenz JR, Hopkins RC, Adams MW (2007) High-Yield Hydrogen Production from Starch and Water by a Synthetic Enzymatic Pathway. PLoS ONE 2(5): e456. doi: 10.1371/journal.pone.0000456



The light duty fleet will transition to electrification via PHEVs. IF automakers make the ICE in those vehicles FFV - the likely green fuel of choice will be E20+ or E85 in those areas where there are pumps.

This idea, while imaginative, appears to need lots of infrastructure. And plain PEM fuel cells are a fine choice if there is a convenient source of H2. This is coming since the E for low temp electrolysis can be cheaply produced via LANR. And there are other physics that make electricity by catalyzing H to lower ground states. Far cheaper than biomass.

But there will be a huge increase in sugar-based alcohol production from Brazil's $12B JV with Shell.


This seems like a build up to promoting the "sugar" fuel cell. When you want the whole world to change to conform to your beliefs, do not hold your breath.


Is a new fuel cell needed, SJC?

It seems to me the key is the bio-reformer. Instead of reconstructing the fuel cell, it seems more that we're reconstructing the hydrogen highway using the sugar-slurry so that current infrastructures can be used.

Nevertheless, the important thing to me is that bridge fuels also have potential long term applications. We can harvest methanol via natural gas and biomass today, but maybe from CO2 or methanogenesis tomorrow, and run that through a methanol fuel cell for optimum efficiency or convert into electricity for plug-ins.

More important, in the short term we can use methanol within the current fueling infrastructure and with current engines, achieving huge gains if coupled with hybrid technologies. However, even in just conventional ICE vehicles its still a domestic, foreign oil fighting fuel.

Cellulosic ethanol poses the same sorts of potential. We can already use within the current fueling infrastructure and long term it could be converted for fuel cell fueling, or converted into electricity for plug-ins.

The point being is that when it comes to things like energy independence, the biggest obstacles are the legacy effects of Americas multi-hundred million fleet of vehicles and our fueling infrastructure. What we're seeing in this kind of research is that there are bridges connecting our energy past to our energy future, and they're available now.

Ultimately, we can achieve great change starting today, while nurturing numerous promising technologies for tomorrow. More important, according to analysis from Accenture, for instance, being able to utilize legacy infrastructures is the key to America's energy future.

The scientific case that such infrastructure-friendly bridge fuels are available today is ample, so for what are we waiting?


WFT?!? Where is biodiesel from algae? Where is butanol from algae starch? Where is combined cycle where multiple outputs (e.g., butanol and biodiesel) are derived from different fractions of the same crop?

Besides cost, fragility to shocks, reliability if they get fouled, and a very slow rate of power production necessitating heavy fuel cells plus large batteries or supercaps to go with them, fuel cells are right around the corner, right?


At 7% efficiency, corn ethanol ICE machines should not even be considered to transport people around.

One could do much better with free sustainable clean sun energy with 20+% solar cells and current BEVs or with PHEVs as an interim solution.

Time to scrap/discard those inefficient, noisy, polluting ICE vehicles, regardless of the type of liquid fuel used.


It does require that you use a fuel cell, the last time I looked there were not 200 million of those out on the road. Gasify biomass, coal and use natural gas to synthesize gasoline and use any car you want.


Well in 2-3 years we will see how the first production fuel cell cars realy do. Then a few years after that we should get a good idea how fast they improve.

To me there are each anouther tool in the box and we need alot of tools. Fuel cells are rather light weight powerful compact and quiet and they last a very long time now some models are going to have 60000 hour warrenties.. that the equive of something like over a million miles.

But what the car variants do this decade.. we cant be sure yet and its gona be FUN finding out how all these techs work out. Its like being at the start of the car all over again.


That may be but it they will probably NOT run on sugar.


Biomass to steam generation to EV for the obvious, practical, simple, win.


When you want the whole world to change to conform to your beliefs, do not hold your breath.

Eff the whole world. How about just the people who care about helping others? The oil cartels have been running the show the last century. That's coming to an end. Their way doesn't work anymore. It's old, inefficient, outdated. But they want to go to war over it. So we will have war. Hellacious, cosmic, espiritus war. And Truth will win.

Resistance is futile.


Fun to drive (3+ton, 300+ hp) ICE vehicles may not be affordable or common place in USA in another 10 years or so if the current economic toward trend continues. Fewer, very basic EV vehicles may be more like it by 2020/2025. The dream (unlimited credit) period may be over.

Will the rest of the world be dragged into the same (wake up) spiral?

Henry Gibson

Just in case there is a reader who has not done the arithmetic, I will invite them to do it soon. There is not enough land area to supply even half of the fuel needed for automobiles with biomass of any kind. It would be better to devote the land area to INFINIA parabolic solar collectors and then feed the electricity to electric cars. An efficient buried direct current microgrid can be invented for this and other purposes. The solar collection efficiency of plants is quite low and does not happen in cold conditions.

Cars can be made to run on powdered charcoal which has quite a good energy density and can be stored for ever. Even aircraft can be made to run on charcoal. Charcoal can be made from any organic material quickly with a process developed in Hawaii.

Most automobile journeys can be made with simple electric automobiles with small batteries. If the journey is too long, a common tiny ICE generator can finish the trip for you at relatively good speeds. An ordinary ICE automobile is used for long distance trips. It can even be rented for that trip and they are very efficient if so driven.

The first step for countries with natural gas is to build factories that produce liquid fuels from methane. The factories can also be converted to coal input if there is not enough methane from natural GAS. Higher efficiency automobiles can make up for the CO2 release. Much higher efficiency hydraulic hybrids have been demonstrated by ARTEMIS no lithium needed, only air tanks. ..HG..

Henry Gibson

Whilst the ARTEMIS HYdrid was demonstrated and is very cleverly adaptable to computer control, this thesis addresses the INNAS HYdrid in detail.


INNAS also developed a free piston hydraulic pump which it is ignoring in their proposed HYdrid.

For energy storage, Parry People Movers use a large slow large flywheel in their successful HYdrid rail vehicles. Some versions run some distance on the flywheel alone. Flywheels were used very successfully to efficiently replace steam locomotives for freight trains in large third rail systems. Most such locomotives were scrapped in full working order after electro-diesel locomotives were perfected and widely used. The flywheel was connected to an efficient motor-generator booster system that allowed operation in and through third rail gaps, and could have allowed regenerative braking.

Gas pressure tanks may be a more energy efficient use than flywheels of high strength fibers and materials. One UPS system used a small flywheel for immediate power and pressure tanks (and hot metal) for longer time power support and engine starting time. ..HG..


To say there is not enough land in the U.S. for all cars is misleading. If there is enough for 1/3 of the cars, that reduces oil imports. All or nothing at all statements miss the point entirely and repeating them over and over just misses the point time and time again.

Everything that we do to reduce oil imports improves the situation. If that is bio and synthetic fuels, good. If that is HEV/PHEV/EV and CAFE, then good. Taking an absolute position that any ONE person has the solution is just blind and egotistical. I have my ideas and others have their ideas, if we work together we might just make progress, but no.


SJC....you know that your statement is misleading, inappropriate and wrongful. Everything you do to reduce oil import will NOT necessarily improve the situation. Using edible feed stocks to produce fuel for our gas guzzlers is NOT the proper solution. The secondary effects would be unsustainable and too many would starve worldwide to allow us to continue to drive our over sized overweight inefficient gas guzzlers.

The real solution is to design and produce much more efficient vehicles, specially electrified vehicles, to reduce the consumption of liquid fuels.



We have been over this before, you use cellulose. You can say more efficient, but that takes decades and we do not have that long.


There are many interim solutions currently available such as a few more million Prius III, IV, V, VI, VII, VIII etc. Many more million Leaf 1, 2, 3, 4, 5, etc. Many more million good PHEVs and BEVs coming to the market place.

The transition will not happen overnight. It will take at least one + vehicle generation (15+ years) and probably two + vehicle generations (30 + years) but we must start now. There is plenty of oil for another 3 to 5 decades, even at close to 100 M/barrel/day but we do not have to burn the last drops right now.


Using edible feed stocks to produce fuel for our gas guzzlers is NOT the proper solution. The secondary effects would be unsustainable and too many would starve worldwide...

Many have proven this a myth. And should the price of meat increase (do to corn feed) it might retard some consumption. Which IS responsible for huge increase in diabetes, heart disease and high blood pressure. So our HEALTH costs decrease.

We remain on the path we have taken for the past five years - developing a portfolio of alternative energy resources. Some make FAR more sense right now than others. But we will continue to build the portfolio with a wide variety of solutions. And become strong and indomitable by doing so.

Energy Independence is here. Resistance is futile.


The world may have lots of oil but we do not. The U.S. uses 25% of the world's oil with only 5% of the people. After 10 years of Prius and a million on the road, that saved us maybe .1% in gasoline consumption but during that time we used more.

The fleet average in the U.S is about 19 mpg, in 10 years it might be 20 or 21 mpg? That is not going to help much. We have enough coal, natural gas and biomass to make synthetic gasoline as well as improve mileage. It is not one or the other. IMO the quickest way is to do both, this is why I mentioned combining methods rather than anyone say they have THE solution.


If coal could be transformed into liquid fuel effectively and CLEANLY, that would sound good for a short time, until we run out of coal or it gets to be too expensive. However, burning coal derived fuel in inefficient ICE vehicles pollutes the environment and has negative effects on our health and well being. To make liquid fuels with edibles is not sustainable. It's like burning the house to make fuel for the gas guzzlers.

We have time to arrive at better solutions, i.e. to progressively replace ICE vehicles with FC and/or electrified units. USA can continue to import crude oil or drive less or buy more efficient vehicles. (it will have no other choice for most of this decade) Making more and more fuel available is not the solution to the growing problem. Its like giving an AA more beer/vodka.


We, the USA, have enough oil (including oil locked up in shale), natural gas and coal for generations of energy use.

So, the change to efficient, alternate energy source transportation may not be as pressing as many believe. At least from a technical standpoint. However, the work needs to be done, and development needs to move forward rapidly. Practical solutions are not only the right thing to do, they can be economic powerhouses too.

Waste is waste.


Shale oil has not proven to be cost effective on a large scale. To count that as a resource is false accounting.



Far from being impossible, oil shale is simply unconventional and more expensive to extract. That in itself does not create a technical impossibility. There are quite a few promising technologies for oil shale. The facts remain, if we need it, we will go for it.


I saw someone count "undiscovered resources" online. I ask how you could quantify that since they are "undiscovered" and got a lot of double talk.

Shale oil has been talked about for decades. Oil has been above $50 per barrel for five years, does it have to be above $100 per barrel for 10 years to make it economical? If so, aren't there better ways to go about conserving and providing alternatives that are more cost effective?

When you hear people talk about shale oil they say we have more oil resources than Saudi Arabia. That is so delusional that no one can even comment on that with a straight face. If they can bring in shale oil cost effectively they would have by now. If not now, when?


I came across this article that compares EV and ICE with BTUs. It is a good explanation of why EVs are still good even though they may be charged using coal fired power plant electricity.


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