A Primer on Hydrogen (H2)
This section provides a basic understanding of hydrogen and the challenges that it has faced in becoming a mainstream fuel.
Hydrogen is a chemical element that has the symbol H and an atomic number of 1. At standard temperature and pressure it is a colorless, odorless, nonmetallic, tasteless, highly flammable diatomic gas (H2). With an atomic mass of 1.00794 g/mol, hydrogen is the lightest element. Hydrogen is the most abundant of the chemical elements, constituting roughly 75% of the universe's elemental mass.
Despite the recent attention focused on the much-anticipated 'Hydrogen Economy', hydrogen is already a significant chemical product in the world today. There are two primary uses for hydrogen, about half is used to produce ammonia (NH3) which is then used directly or indirectly as fertilizer. Now more increasingly, hydrogen is being used to convert low-grade crude oils into lighter fractions as fuels, known as hydro-cracking, since rising oil prices have forced oil companies to extract from poorer sources, such as tar sands and oil shale.
World production for hydrogen estimates are approximately 50 million tons per year, (about 170 million tons of oil equivalent), growing at about 10% annually. As of 2005, the economic value of all hydrogen produced worldwide represents approximately $135 billion per year.
Traditional Sources of Hydrogen
Virtually all hydrogen is made from natural gas, whereby steam methane reforming accounts for 95% of the hydrogen produced in the U.S. Other methods of hydrogen production are gasification of fossil fuels (e.g. coal), splitting water using electricity (electrolysis - which requires low voltage electricity and is currently uneconomical), heat or light, and thermal or biological conversion of biomass.
Challenges to the Hydrogen Economy
The 'Hydrogen Economy' has therefore three inherent limitations based on current methods of hydrogen production - continued reliance on fossil fuels, greenhouse emissions and cost. If hydrogen were to be the alternative fuel of the future, these current production methods would fall far short of their intended goal.
Reliance on Fossil Fuels
All current commercial methods of producing hydrogen rely on the consumption of fossil fuels - a non-renewable resource. Steam reformation is dependent on a source of natural gas (methane), while electrolysis requires a significant amount of electricity to split the strong water molecule. The majority of electricity, over 70%, comes from a number of fossil fuel powered, non-renewable sources such as; coal-fired steam plants (50.8%), natural gas (16.7%), petroleum (3.1%)1 . Therefore, all traditional commercial methods of hydrogen production are dependent on non-renewable and declining resources.
Greenhouse Emissions
Despite the popularity of steam reformation to produce hydrogen (95%), the process also produces significant carbon dioxide emissions and requires excessive electrical power to operate the reformer. In the USA alone, 11 Mt/yr of hydrogen production consumes 5% of US natural gas usage, releasing 77 Mt CO2. The predicted use of hydrogen for all US transport is expected to require some 200 Mt/yr of hydrogen. Based on these figures alone, one can easily extrapolate the enormous amount of carbon dioxide which would be released into the atmosphere. This figure is just to meet US transport requirements, not to mention the negative effects of a variety of other applications which could depend on this form of hydrogen production.
Cost
Hydrogen is also expensive to produce and when compared to gasoline, based on energy equivalency, it is double the existing retail price in the USA. Electrolytic- produced hydrogen costs around $30/mBtu, natural gas reformed hydrogen about $3/mBtu, and gasoline reformed hydrogen about $9/mBtu. Some analysts have speculated that widespread hydrogen use will not occur until the price of gas/oil increases beyond the price of hydrogen. However, it can be safely predicted that as the prices of fossil-fuels continue to rise, fossil-fuel based hydrogen production costs must also increase. In this scenario, hydrogen has little chance to ever be more economical than gasoline, unless an alternative method of production is made available.
Conclusions
Despite its hydrogen's numerous environmental advantages and potential, hydrogen must also become affordable before it is accepted as an alternative energy carrier.
1http://www.eia.doe.gov/cneaf/electricity/epa/epa_sum.html
Energy Information Administration, Electric Power Annual (Electric Power Annual with data for 2005) (See Appendix No. 31)
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