Hydrogen vehicle

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Hydrogen vehicle
Hydrogen fueling

A hydrogen vehicle is a vehicle that uses hydrogen as its on-board fuel for motive power. The term may refer to a personal transportation vehicle, such as an automobile, or any other vehicle that uses hydrogen in a similar fashion, such as an aircraft. The power plants of such vehicles convert the chemical energy of hydrogen to mechanical energy (torque) in one of two methods: combustion, or electrochemical conversion in a fuel-cell:


[edit] Vehicles

Buses, trains, PHB bicycle, cargo bikes, golf carts, motorcycles, wheelchairs, ships, airplanes, submarines, high-speed cars, and rockets can already run on hydrogen, in various forms and sometimes at great expense. NASA uses hydrogen to launch Space Shuttles into space. There is even a working toy model car that runs on solar power, using a regenerative fuel cell to store energy in the form of hydrogen and oxygen gas. It can then convert the fuel back into water to release the solar energy.[1]

The current land speed record for a hydrogen-powered vehicle is 333.38 km/h (207.2 mph) set by a prototype Ford Fusion Hydrogen 999 Fuel Cell Race Car at Bonneville Salt Flats in Wendover, Utah in August 2007. It was accompanied by a large compressed oxygen tank to increase power. Honda has also created a concept called the FC Sport, which may be able to beat that record if put into production.[2]

[edit] Automobiles

Sequel, a fuel cell-powered vehicle from General Motors
Ford Edge hydrogen-electric plug-in hybrid concept

Many companies are currently researching the feasibility of building hydrogen cars, and most of the automobile manufacturers had begun developing hydrogen cars, see list of fuel cell vehicles. However, the Ford Motor Company has dropped its plans to develop hydrogen cars, stating that "The next major step in Ford’s plan is to increase over time the volume of electrified vehicles".[3] Similarly, French Renault-Nissan announced in February 2009 that it is cancelling its hydrogen car R&D efforts.[4] In the same month Nissan started testing a new FC vehicle in Japan.[5]

Most hydrogen cars are currently only available in demonstration models or in a lease construction in limited numbers and are not yet ready for general public use. The recorded number of hydrogen-powered public vehicles in the United States was 200 as of April 2007, mostly in California.[6] Funding has come from both private and government sources. In May 2008, Wired News reported that "experts say it will be 40 years or more before hydrogen has any meaningful impact on gasoline consumption or global warming, and we can't afford to wait that long. In the meantime, fuel cells are diverting resources from more immediate solutions."[7]

Daimler starts its FC vehicle production in 2009 with the aim of 100.000 vehicles in 2012-2013[8][9]. Hyundai will produce 500 FC vehicles by 2010 and expects to start mass production of its FC vehicles in 2012[10].

[edit] Buses

Fuel cell buses (as opposed to hydrogen fueled buses) are being trialed by several manufacturers in different locations. The Fuel Cell Bus Club is a global fuel cell bus testing collaboration.

Hydrogen was first stored in roof mounted tanks, although models are now incorporating inboard tanks. Some double deck models uses between floor tanks.

[edit] Bicycles

Pearl Hydrogen Power Sources of Shanghai,People's Republic of China, unveiled a hydrogen bicycle at the 9th China International Exhibition on Gas Technology, Equipment and Applications in 2007.

[edit] Motorcycles

ENV is developing electric motorcycles powered by a hydrogen fuel cell, including the Crosscage and Biplane.

The Boeing Fuel Cell Demonstrator powered by a hydrogen fuel cell

[edit] Tractors

New Holland’s innovation and commitment to renewable energy was recently acknowledged at the SIMA Innovation Awards winning a Gold Medal for an impressively designed NH2 hydrogen powered tractor. Look at : New Holland Wins Gold for Energy Independent Farm Concept or Hydrogen-powered tractor in an Energy Independent Farm

[edit] Airplanes

Companies such as Boeing and Smartfish are pursuing hydrogen as fuel for airplanes. Unmanned hydrogen planes have been tested, and in February 2008 Boeing tested a manned flight of a small aircraft powered by a hydrogen fuel cell. The Times reported that "Boeing said that hydrogen fuel cells were unlikely to power the engines of large passenger jets but could be used as backup or auxiliary power units onboard."[11]

In Europe, the Reaction Engines A2 has been proposed to use the thermodynamic properties of liquid hydrogen to achieve very high speed, long distance (antipodal) flight by burning it in a precooled jet engine.

[edit] Rockets

Rockets employ hydrogen because hydrogen gives the highest effective exhaust velocity as well as giving a lower net weight of propellant than other fuels. It particularly shines on upper stages, although it has been used on lower stages as well, usually in conjunction with a dense fuel booster.

The main disadvantage of hydrogen in this application is the low density and deeply cryogenic nature, requiring insulation- this makes the hydrogen tanks relatively heavy, which greatly offsets much of the otherwise overwhelming advantages for this application.

The main advantage of hydrogen is that although the delta-v of a stage employing it is little different to a dense fuelled stage, the GLOW of the stage is rather less. This makes any lower stages lighter.

[edit] Internal combustion vehicle

Hydrogen internal combustion engine cars are different from hydrogen fuel cell cars. The hydrogen internal combustion car is a slightly modified version of the traditional gasoline internal combustion engine car. These hydrogen engines burn fuel in the same manner that gasoline engines do.

Francois Isaac de Rivaz designed in 1807 the first internal combustion engine on hydrogen[12] Paul Dieges patented In 1970 a modification to internal combustion engines which allowed a gasoline-powered engine to run on hydrogen US patent 3844262.

Mazda has developed Wankel engines that burn hydrogen. The advantage of using ICE (internal combustion engine) such as wankel and piston engines is that the cost of retooling for production is much lower. Existing-technology ICE can still be used to solve those problems where fuel cells are not a viable solution as yet, for example in cold-weather applications.

HICE forklift trucks have been demonstrated [13] based on converted diesel internal combustion engines with direct injection[14].

[edit] Fuel cell

While fuel cells themselves are potentially highly energy efficient, and working prototypes were made by Roger E. Billings in the 1960s, at least four technical obstacles and other political considerations exist regarding the development and use of a fuel cell-powered hydrogen car.

[edit] Fuel cell cost

Currently, hydrogen fuel cells are costly to produce and are fragile. Engineers are studying how to produce inexpensive fuel cells that are robust enough to survive the bumps and vibrations that all automobiles experience. Also, many designs require rare substances such as platinum as a catalyst in order to work properly. Such a catalyst can also become contaminated by impurities in the hydrogen supply. In the past few years, however, a nickel-tin nanometal catalyst has been under development which may lower the cost of cells.[15]

Fuel cells are generally priced in USD/kW, and data is scarce regarding costs. Ballard Power Systems is virtually alone in publishing such data. Their 2005 figure was $73 USD/kW (based on high volume manufacturing estimates), which they said was on track to achieve the U.S. DoE's 2010 goal of $30 USD/kW. This would achieve closer parity with internal combustion engines for automotive applications, allowing a 100 kW fuel cell to be produced for $3000. 100 kW is about 134 hp.[16]

[edit] Freezing conditions

Temperatures below freezing (32 °F or 0 °C) are a major concern with fuel cells operations. Operational fuel cells have an internal vaporous water environment that could solidify if the fuel cell and contents are not kept above 0 Celsius ( 32 F). Most fuel cell designs are not as yet robust enough to survive in below freezing environments. Frozen solid, especially before start up, they would not be able to begin working. Once running though, heat is a byproduct of the fuel cell process, which would keep the fuel cell at an adequate operational temperature to function correctly. This makes startup of the fuel cell a major concern in cold weather operation. Places such as Canada or Alaska where temperatures can reach -40C ( -40F) at startup would not be able to use early model fuel cells. Ballard announced that it has already hit the U.S. DoE's 2010 target for cold weather starting which was 50% power achieved in 30 seconds at -20 °C.[17] Possibly the incorporation of a preheat device would help to lessen such problems if the energy drain was not too great on the vehicle's batteries, or alternately the combustion of hydrogen similar to a small furnace type device. Another avenue could be the use of a different type of fuel cell that has a membrane that acts as a heating element that almost instantaneously heats up to the correct temperate to start the h2 process. There are different kinds of fuel cells that work at both different temperatures and catalysts. This membrane would be heated by the car battery since it is so thin the process would be quick. Membranes presently only work in a low temperature manner. This would require an extra exhaust outlet in case of water ice blockage in the fuel cell, a minor consideration.

Just as early gasoline cars struggled with efficiency and reliability problems before becoming universally practical, so fuel cells have to work out startup and long term reliability problems. Early gasoline engines had the characteristic of higher heat dissapation once running, where as fuels cells emit less heat, making the warm up process somewhat less quick.[18]

[edit] Service life

Although service life is coupled to cost, fuel cells have to be compared to existing machines with a service life in excess of 5000 hours[19] for stationary and light-duty. Marine PEM fuel cells reached the target in 2004[20]. Current service life is 7,300 hours under cycling conditions[21]. Research is going on especially for heavy duty like in the bus trials which are targeted up to a service life of 30,000 hours.

[edit] Hydrogen

[edit] Production

The molecular hydrogen needed as an on-board fuel for hydrogen vehicles can be obtained through many thermochemical methods utilizing natural gas, coal (by a process known as coal gasification), liquefied petroleum gas, biomass (biomass gasification), by a process called thermolysis, or as a microbial waste product called biohydrogen or Biological hydrogen production. Most of today's hydrogen is produced using fossil energy resources,[22] and 85% of hydrogen produced is used to remove sulfur from gasoline. Hydrogen can also be produced from water by electrolysis or by chemical reduction using chemical hydrides or aluminum.[23] Current technologies for manufacturing hydrogen use energy in various forms, totaling between 25 and 50 percent of the higher heating value of the hydrogen fuel, used to produce, compress or liquefy, and transmit the hydrogen by pipeline or truck.[24] Electrolysis, currently the most inefficient method of producing hydrogen, uses 65 to 112 percent of the higher heating value on a well-to-tank basis.[25]

Environmental consequences of the production of hydrogen from fossil energy resources include the emission of greenhouse gases, a consequence that would also result from the on-board reforming of methanol into hydrogen. Studies comparing the environmental consequences of hydrogen production and use in fuel-cell vehicles to the refining of petroleum and combustion in conventional automobile engines find a net reduction of ozone and greenhouse gases in favor of hydrogen.[26] Hydrogen production using renewable energy resources would not create such emissions or, in the case of biomass, would create near-zero net emissions assuming new biomass is grown in place of that converted to hydrogen. However the same land could be used to create Biodiesel, usable with (at most) minor alterations to existing well developed and relatively efficient diesel engines. In either case, the scale of renewable energy production today is small and would need to be greatly expanded to be used in producing hydrogen for a significant part of transportation needs.[27] As of December 2008, less than 3 percent of U.S. electricity was produced from renewable sources, not including dams.[28] In a few countries, renewable sources are being used more widely to produce energy and hydrogen. For example, Iceland is using geothermal power to produce hydrogen,[29] and Denmark is using wind.[30]

In addition to the inherent losses of energy in the conversion of feed stock to produce hydrogen, which makes hydrogen less advantageous as an energy carrier, there are economic and energy penalties associated with packaging, distribution, storage and transfer of hydrogen.[31]

[edit] Storage

Compressed hydrogen storage mark

Hydrogen has a very low volumetric energy density at ambient conditions, equal to about one-third that of methane. Even when the fuel is stored as liquid hydrogen in a cryogenic tank or in a compressed hydrogen storage tank, the volumetric energy density (megajoules per liter) is small relative to that of gasoline. Hydrogen has a three times higher energy density by mass compared to gasoline (143 MJ/kg versus 46.9 MJ/kg). Because of the energy required to compress or liquefy the hydrogen gas, the supply chain for hydrogen has lower well-to-wheel efficiency but a higher tank-to-wheel compared to gasoline IC's.[31] Some research has been done into using special crystalline materials to store hydrogen at greater densities and at lower pressures. A recent study by Dutch researcher Robin Gremaud has shown that metal hydride hydrogen tanks are actually 40 to 60-percent lighter than a equivalent energy battery pack on an electric vehicle permitting greater range for H2 cars.[32]

[edit] Infrastructure

The hydrogen infrastructure consists mainly of industrial hydrogen pipeline transport and hydrogen-equipped filling stations like those found on a hydrogen highway. Hydrogen stations which are not situated near a hydrogen pipeline get supply via hydrogen tanks, compressed hydrogen tube trailers, liquid hydrogen tank trucks or dedicated onsite production.

Hydrogen use would require the alteration of industry and transport on a scale never seen before in history. For example, according to GM, 70% of the U.S. population lives near a hydrogen-generating facility but has just about no access to hydrogen, despite its wide availability for commercial use.[33] The distribution of hydrogen fuel for vehicles in the U.S. would require new hydrogen stations costing, by some estimates, 20 billion dollars.[34] and 4.6 billion in the EU.[35] Other estimates place the cost as high as half trillion U.S. dollars in the United States alone.[36]

[edit] Codes and standards

Hydrogen codes and standards are codes and standards (RCS) for hydrogen fuel cell vehicles.

Additional to the codes and standards for hydrogen vehicles, there are codes and standards for hydrogen safety, for the safe handling of hydrogen and the storage of hydrogen.

Codes and standards have repeatedly been identified as a major institutional barrier to deploying hydrogen technologies and developing a hydrogen economy. To enable the commercialization of hydrogen in consumer products, new model building codes and equipment and other technical standards are developed and recognized by federal, state, and local governments.[37]

[edit] Economy

Hydrogen does not come as a pre-existing source of energy like fossil fuels, but rather as a carrier, much like a battery. It can be made from both renewable and non-renewable energy sources. The common internal combustion engine, usually fueled with gasoline (petrol) or diesel liquids, can be converted to run on gaseous hydrogen. However, the more energy efficient use of hydrogen involves the use of fuel cells and electric motors. Hydrogen reacts with oxygen inside the fuel cells, which produces electricity to power the motors. A primary area of research is hydrogen storage, to try to increase the range of hydrogen vehicles, while reducing the weight, energy consumption, and complexity of the storage systems. Two primary methods of storage are metal hydrides and compression.

A potential advantage of hydrogen is that it could be produced and consumed continuously, using solar, water, wind and nuclear power for electrolysis. Currently, however, hydrogen vehicles utilizing hydrogen produce more pollution than vehicles consuming gasoline, diesel, or methane in a modern internal combustion engine, and far more than plug-in hybrid electric vehicles.[31][38] This is because, although hydrogen fuel cells generate no CO2, production of the hydrogen creates additional emissions.[39] While methods of hydrogen production that do not use fossil fuel would be more sustainable,[40] currently such production is not economically feasible, and diversion of renewable energy (which represents only 2% of energy generated) to the production of hydrogen for transportation applications is inadvisable.[38]

The production of hydrogen with electricity makes it an energy carrier, and not an energy source, so the energy the car uses would ultimately need to be provided by a conventional power plant or a home hydrogen station. A suggested benefit of large-scale deployment of hydrogen vehicles is that it could lead to decreased emissions of greenhouse gases and ozone precursors.[26] Further, the conversion of fossil fuels would be moved from the vehicle, as in today's automobiles, to centralized power plants in which the byproducts of combustion or gasification may be better controlled than at the tailpipe.

[edit] Criticism

Critics charge that the time frame for overcoming the technical and economic challenges to implementing wide-scale use of hydrogen vehicles is likely to be at least several decades, and hydrogen vehicles may never become broadly available.[38][41] They believe that the focus on the use of the hydrogen car is a dangerous detour from more readily available solutions to reducing the use of fossil fuels in vehicles.[42] K. G. Duleep speculates that "a strong case exists for continuing fuel-efficiency improvements from conventional technology at relatively low cost."[43] Critiques of hydrogen vehicles are presented in the 2006 documentary, Who Killed the Electric Car?. According to former U.S. Department of Energy official Joseph Romm, "A hydrogen car is one of the least efficient, most expensive ways to reduce greenhouse gases." Asked when hydrogen cars will be broadly available, Romm replied: "Not in our lifetime, and very possibly never."[43] The Los Angeles Times wrote, in February 2009, "Hydrogen fuel-cell technology won't work in cars.... Any way you look at it, hydrogen is a lousy way to move cars.[44]

As an article published in the March/April 2007 issue of Technology Review stated,

In the context of the overall energy economy, a car like the BMW Hydrogen 7 would proba­bly produce far more carbon dioxide emissions than gasoline-powered cars available today. And changing this calculation would take multiple breakthroughs--which study after study has predicted will take decades, if they arrive at all. In fact, the Hydrogen 7 and its hydrogen-fuel-cell cousins are, in many ways, simply flashy distractions produced by automakers who should be taking stronger immediate action to reduce the greenhouse-gas emissions of their cars.[38]

The Wall Street Journal reported in 2008 that "Top executives from General Motors Corp. and Toyota Motor Corp. Tuesday expressed doubts about the viability of hydrogen fuel cells for mass-market production in the near term and suggested their companies are now betting that electric cars will prove to be a better way to reduce fuel consumption and cut tailpipe emissions on a large scale."[45] In addition, Ballard Power Systems, a leading developer of hydrogen vehicle technology, pulled out of the Hydrogen vehicle business in late 2007. Research Capital analyst Jon Hykawy concluded that Ballard saw the industry going nowhere and said: "In my view, the hydrogen car was never alive. The problem was never could you build a fuel cell that would consume hydrogen, produce electricity, and fit in a car. The problem was always, can you make hydrogen fuel at a price point that makes any sense to anybody. And the answer to that to date has been no."[46]

The Economist magazine in September 2008, quoted Robert Zubrin, the author of Energy Victory, as saying: "Hydrogen is 'just about the worst possible vehicle fuel'".[47] The magazine noted the retirement of Ballard from the industry and the withdrawal of California from earlier goals: "In March [2008] the California Air Resources Board, an agency of California's state government and a bellwether for state governments across America, changed its requirement for the number of zero-emission vehicles (ZEVs) to be built and sold in California between 2012 and 2014. The revised mandate allows manufacturers to comply with the rules by building more battery-electric cars instead of fuel-cell vehicles."[47] The magazine also noted that most hydrogen is produced through steam reformation, which creates at least as much emission of carbon per mile as some of today's gasoline cars. On the other hand, if the hydrogen could be produced using renewable energy, "it would surely be easier simply to use this energy to charge the batteries of all-electric or plug-in hybrid vehicles."[47]

Despite these criticisms, Honda Motors announced on March 30, 2009 that it will put resources into hydrogen fuel cell development, which it sees as "a better long term bet than batteries and plug-in vehicles".[48]

[edit] Alternatives


ICE-based hybrid cars can be plugged into the electric grid (Plug-in hybrid electric vehicles, or PHEVs) and achieve much higher overall gas mileage and lower emissions than other hybrids. A 2006 article in Scientific American argues that PHEVs, rather than hydrogen vehicles, will soon become standard in the automobile industry.[49] PHEVs are gaining traction as an alternative to hydrogen.[50] PHEV designs augment today's hybrid gasoline-electric vehicles with greater battery capacity to enable increased use of the vehicle's electric traction motor and reduced reliance on the combustion engine. The batteries are charged via the electric grid when the vehicle is parked. Electric power transmission is about 93 percent efficient [51] and the infrastructure is already in place.[52]


ICE-based CNG or LNG vehicles (Natural gas vehicles or NGVs) use Natural gas or Biogas as a fuel source. Natural gas has a higher energy density than hydrogen gas and has only water and carbon dioxide as waste products. Since the majority of home hydrogen refuelling systems use natural gas as a source for hydrogen, natural gas powered vehicles are easily demonstrated to have a lower carbon dioxide footprint. When using Biogas, NGVs become carbon neutral vehicles which run on animal waste [53]. Manufacturing NGVs do not require any toxic materials as the engine is essentially the same as a conventional gasoline engine unlike fuel cells or high capacity batteries, which may cause environmental issues during manufacturing or disposal[54]. Unlike hydrogen, CNG vehicles have been available for several years and in many places, there is sufficient infrastructure to provide refueling stations in addition to the home refueling systems. The ACEEE has rated the Honda Civic GX, which only uses compressed natural gas, as the greenest vehicle currently available. [55] [56] [57]


Electric cars, such as the General Motors EV1 are typically more efficient than fuel cell-powered vehicles on a well-to-wheel basis.[58][59] As Technology Review noted in June 2008, "Electric cars—and plug-in hybrid cars—have an enormous advantage over hydrogen fuel-cell vehicles in utilizing low-carbon electricity. That is because of the inherent inefficiency of the entire hydrogen fueling process, from generating the hydrogen with that electricity to transporting this diffuse gas long distances, getting the hydrogen in the car, and then running it through a fuel cell—all for the purpose of converting the hydrogen back into electricity to drive the same exact electric motor you'll find in an electric car." Simply stating the governing laws of Thermodynamics decreases the overall efficiency of any given process with each additional step in reaction.[60][61]

[edit] See also

[edit] References

  1. ^ Thames & Kosmos kit, Other educational materials, and many more demonstration car kits.
  2. ^ New Hydrogen-Powered Land Speed Record from Ford
  3. ^ "Ford Motor Company Business Plan", December 2, 2008
  4. ^ Dennis, Lyle. "Nissan Swears Off Hydrogen and Will Only Build Electric Cars", All Cars Electric, February 26, 2009
  5. ^ Nissan Starts Vehicle Testing of New Fuel-cell Technology
  6. ^ GaleGroup.com info
  7. ^ Squatriglia, Chuck. "Hydrogen Cars Won't Make a Difference for 40 Years", Wired, May 12, 2008
  8. ^ Produktion der Brennstoffzelle beginnt schon im Sommer (German)
  9. ^ Daimler starts small series production of fuel cell vehicles in summer 2009
  10. ^ [http://blog.wired.com/cars/2008/03/hyundai-will-ha.html Hyundai Will Have Hybrids Next Year - And Fuel Cells in 2012?[
  11. ^ David Robertson (2008-04-03). "Boeing tests first hydrogen powered plane". The Times. http://business.timesonline.co.uk/tol/business/industry_sectors/transport/article3675188.ece. 
  12. ^ 1807 Francois Isaac de Rivaz - internal combustion engine
  13. ^ Linde X39
  14. ^ HyICE
  15. ^ "COE researchers engineer low-cost catalyst for hydrogen production"
  16. ^ Ballard "2006 achievements" press release
  17. ^ From the Ballard website
  18. ^ United States Department of Energy, http://www1.eere.energy.gov/hydrogenandfuelcells/
  19. ^ EERE Service life 5000 hours
  20. ^ Marine PEM fuel cell service life
  21. ^ DOE fuel cell school bus june 2008 Pag 9
  22. ^ Air Products and Chemicals website
  23. ^ L. Soler, J. Macanás, M. Muñoz, J. Casado. Journal of Power Sources 169 (2007) 144-149
  24. ^ F. Kreith (2004). "Fallacies of a Hydrogen Economy: A Critical Analysis of Hydrogen Production and Utilization". Journal of Energy Resources Technology 126: 249–257.
  25. ^ Ulf Bossel,Energy and the Hydrogen Economy
  26. ^ a b Schultz, M.G., Thomas Diehl, Guy P. Brasseur, and Werner Zittel. Air Pollution and Climate-Forcing Impacts of a Global Hydrogen Economy. Science 24 October 2003 302: 624-627[1]
  27. ^ US Energy Information Administration, "World Primary Energy Production by Source, 1970-2004"
  28. ^ Galbraith, Kate and Matthew L. Wald. "Energy Goals a Moving Target for States", The New York Times, December 4, 2008
  29. ^ Iceland's hydrogen buses zip toward oil-free economy accessed 17-July-2007
  30. ^ First Danish Hydrogen Energy Plant Is Operational accessed 17-July-2007
  31. ^ a b c EFCF paper on hydrogen efficiency
  32. ^ Light Weight Hydrogen 'Tank' Could Fuel Hydrogen Economy
  33. ^ Henry, Jim (October 29, 2007). ""GM's Fuel-Cell Hedge"". BusinessWeek. http://www.businessweek.com/autos/content/oct2007/bw20071026_550384.htm?chan=autos_hybrids+index+page_news+%3Cspan+style%3D%22font-family%3Aarial%3B%22%3E%2B%3C%2Fspan%3E+features. Retrieved on 2008-05-09. 
  34. ^ Gardner, Michael (November 22, 2004). ""Is 'hydrogen highway' the answer?"". San Diego Union-Tribune. http://www.signonsandiego.com/news/science/20041122-9999-1n22hydrogen.html. Retrieved on 2008-05-09. 
  35. ^ Stanley, Dean. "Shell Takes Flexible Approach to Fueling the Future". hydrogenforecast.com. http://www.hydrogenforecast.com/ArticleDetails.php?articleID=250. Retrieved on 2008-05-09. 
  36. ^ Romm, Joseph (2004). The Hype about Hydrogen, Fact and Fiction in the Race to Save the Climate. New York: Island Press.  (ISBN 1-55963-703-X), Chapter 5
  37. ^ DOE codes and standards
  38. ^ a b c d From TechnologyReview.com "Hell and Hydrogen", March 2007
  39. ^ See Novelli, P.C., P.M. Lang, K.A. Masarie, D.F. Hurst, R. Myers, and J.W. Elkins. (1999). "Molecular Hydrogen in the troposphere: Global distribution and budget". J. Geophys. Res. 104(30): 427-30.
  40. ^ F. Kreith, "Fallacies of a Hydrogen Economy: A Critical Analysis of Hydrogen Production and Utilization" in Journal of Energy Resources Technology (2004), 126: 249–257.
  41. ^ Squatriglia, Chuck (May 12, 2008). ""Hydrogen Cars Won't Make a Difference for 40 Years"". Wired. CondéNet, Inc. http://www.wired.com/cars/energy/news/2008/05/hydrogen. Retrieved on 2008-05-13. 
  42. ^ White, Charlie. "Hydrogen fuel cell vehicles are a fraud" Dvice TV, July 31, 2008
  43. ^ a b Boyd, Robert S. (May 15, 2007). ""Hydrogen cars may be a long time coming"". McClatchy Newspapers. http://www.mcclatchydc.com/staff/robert_boyd/story/16179.html. Retrieved on 2008-05-09. 
  44. ^ Neil, Dan (February 13, 2009). "Honda FCX Clarity: Beauty for beauty's sake". Los Angeles Times. http://www.latimes.com/classified/automotive/highway1/la-fi-neil13-2009feb13,0,6636491.story. Retrieved on 2009-03-11. 
  45. ^ GM, Edward Taylor and Mike Spector. "Toyota Doubtful on Fuel Cells' Mass Use", The Wall Street Journal, March 5, 2008
  46. ^ Article on Ballard's exit from the hydrogen vehicle industry
  47. ^ a b c Wrigglesworth, Phil. "The car of the perpetual future"' September 4, 2008, retrieved on September 15, 2008
  48. ^ Abuelsamid, Sam. "Honda pulls out of Frankfurt to save costs, starts testing FCX in Germany", AutoBloggreen, April 2 2009
  49. ^ Romm, Joseph and Prof. Andrew A. Frank "Hybrid Vehicles Gain Traction", Scientific American (April 2006)
  50. ^ Plug-in Hybrid Advocacy Group
  51. ^ Powerwatch - Domestic Energy use in the UK
  52. ^ US government news release
  53. ^ "Car Fueled With Biogas From Cow Manure: WWU Students Convert Methane Into Natural Gas"
  54. ^ "An investigation into end-of-life management of solid oxide fuel cells"
  55. ^ "ACEEE Greenest Vehicles of 2008"
  56. ^ "The Cleanest Cars on Earth?: Honda Civic GX and Other Natural Gas Vehicles (NGVs)"
  57. ^ "Honda Civic GX Natural Gas Car Earns Top Spot on ACEEE's "Greenest Vehicles of 2008" List for the Fifth Straight Year"
  58. ^ "Efficiency of Hydrogen PEFC, Diesel-SOFC-Hybrid and Battery Electric Vehicles" (PDF). 2003-07-15. http://www.efcf.com/reports/E04.pdf. Retrieved on January 7, 2009. 
  59. ^ Information from cta.ornl.gov
  60. ^ "The Last Car You Would Ever Buy – Literally: Why we shouldn't get excited by the latest hydrogen cars", Technology Review, June 18, 2008
  61. ^ Energy efficiency comparison article

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