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Hydrogen economy

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A hydrogen economy is a hypothetical future economy in which energy, for mobile applications (vehicles, aircraft) and electrical grid load balancing (daily peak demand reserve), is stored as hydrogen (H2).

Rationale

A hydrogen economy is desired in order to solve the problems of energy supply and the ill effects of using hydrocarbon fuels.

Petroleum, which accounts for most of the hydrocarbons imported by industrialized countries, is refined into gasoline and diesel fuels to be used in automobiles and aircraft. Other hydrocarbon fuels, such as coal and natural gas, are burned for the generation of electricity. The burning of hydrocarbon fuels causes the emission of greenhouse gases and other pollutants. Furthermore, the remaining supply of hydrocarbon resources in the world is limited, and the demand for hydrocarbon fuels is increasing, particularly in China, India and other developing countries.

Hydrogen has been proposed as a replacement for these fuels once alternative energy sources have been identified.

Grid load balancing of electricity is a major issue in energy supply. Currently, this is done by varying the output of generators. However, electricity is hard to store efficiently for future use. The most cost-efficient and widespread system for large-scale grid energy storage is pumped storage, that is, pumping water up to a dam reservoir and generating electricity on demand from that via hydropower. However such systems will not scale down to portable applications. Smaller storage alternatives such as capacitors have very low energy density. Batteries have low energy density and are slow to charge and discharge. Flywheel power storage can be more efficient than batteries with about the same size, but there are safety concerns due to explosive shattering.

Because of the efficiency of internal combustion engines burning high energy density hydrocarbon fuels, automobiles and aircraft nearly all run on hydrocarbon fuels. Fears that sources of hydrocarbon fuels will run out and concerns over global warming due to carbon dioxide (CO2) tailpipe emissions have given rise to a search for an alternative fuel to hydrocarbon fossils which does not have these problems.

Some believe that fuel cells, using hydrogen as a fuel, will be able to replace most internal combustion engines and will be able to solve most grid load balancing needs in the future.

Hydrogen is the most abundant element in the universe. It also has an excellent energy density by weight, which leads to it being used for spaceships like the space shuttle. Emissions of a hydrogen-oxygen fuel cell, in theory, consist of pure water. The fuel cell is also more efficient than an internal combustion engine. The internal combustion engine is said to be 20-30% efficient, while the fuel cell is 75-80% efficient (not accounting for losses in the actual production of hydrogen)and together with the electric motor and controller the drivetrain overall efficiency approaches 40% with low idling losses.

Present hydrogen market

Hydrogen production is a large and growing industry. Globally, some 50 million metric tons of hydrogen, containing 200 gigawatts of energy, were produced in 2004. The growth rate is around 10% per year. Within the United States, production was about 11 million metric tons, containing 48 gigawatts of energy. (The total electric production in 2003 was some 442 gigawatts by comparison.) Because hydrogen storage and transport is expensive, most hydrogen is currently produced locally, and used immediately, generally by the same company producing it. As of 2005, the economic value of all hydrogen produced is about $135 billion per year.

There are two primary uses for hydrogen today. About half is used to produce ammonia (NH3) via the Haber process, which is then used directly or indirectly as fertilizer. Because the world population and the intensive agriculture used to support it are both growing, ammonia demand is growing. The other half of current hydrogen production is used to convert heavy petroleum sources into lighter fractions suitable for use as fuels. This latter process is known as hydrocracking. Hydrocracking represents an even larger growth area, since rising oil prices encourage oil companies to extract poorer source material, such as tar sands and oil shale.

Currently, hydrogen production is 48% from natural gas, 30% from oil, and 18% from coal; water electrolysis accounts for only 4%.

The large market and sharply rising prices have also stimulated great interest in alternate, cheaper means of hydrogen production.

Envisioned centralized hydrogen sources

A hydrogen economy would use non-fossil energy sources to produce hydrogen gas as a stored energy source for use in various sectors of the economy. If energy were in place to produce the hydrogen, then hydrogen could be used as an intermediate energy storage form to replace greenhouse-gas emitting alternatives like gas and oil.

Large rural high-efficiency hydrogen generators would combine with a distribution system. This system would be similar to today's natural gas distribution system but upgraded to meet hydrogen's additional transport challenges. At the intermediate energy-distributer and end-user level, fuel cells that run on hydrogen might be able to replace today's local electrical distribution and generation systems or fuel vehicles. Similar systems are currently used with natural gas to produce electricity in large urban developments with cogeneration facilities.

The primary energy source for producing hydrogen could be nuclear, or fossil fuel. In a full hydrogen economy, even primary electrical sources like hydro and wind power might be used to make hydrogen, instead of tapping directly into the electrical grid. (The proper balance between hydrogen distribution and long-distance electrical distribution is one of the primary questions that arises in the hydrogen economy.) Large generators that produced hydrogen from fossil fuel energy sources generate huge amounts of pollution, but they also centralize emissions, so emission control systems would be easier to inspect and hence perhaps better maintained than systems on automobiles owned by individuals.

Fuel cells

The underlying premise of a hydrogen economy is that fuel cells will replace internal combustion engines and turbines as the primary way to convert chemical power into motive and electrical power. The reason to expect this changeover is that fuel cells, being electrochemical, can be more efficient than heat engines. Currently, fuel cells are very expensive, but there is active research to bring down fuel cell prices.

Fuel cells work with hydrocarbon fuels as well as pure hydrogen. If and when fuel cells become cost-competitive with internal combustion engines and turbines, one of the first adopters will be large gas-fired power plants. These are currently being built in large numbers by a highly competitive industry, their owners can work with operational constraints (tight temperature ranges, low shock, slow power ramps, etc), power to weight is not an issue, and even small efficiency gains are worth quite a lot. If reforming natural gas into hydrogen and then using that hydrogen in a fuel cell is somehow more efficient than burning the natural gas, gas-fired powerplants will do that instead.

Much of the popular interest in hydrogen seems to attach to the idea of using fuel cells in automobiles. The cells can have a good power-to-weight ratio, are more efficient than internal combustion engines, and produce no damaging emissions. If safe hydrogen storage can be found, and cheap fuel cells can be manufactured, they may be economically viable in an advanced hybrid automobile (hybrid in the sense of fuel-cell/battery combination).

So long as methane is the primary source of hydrogen, it will make more sense to fill specialized car tanks with compressed methane and run the fuel cells directly from that. The resulting system uses the methane energy more efficiently, produces less total CO2, and requires less new infrastructure. A further advantage is that methane is much easier to transport and handle than hydrogen. Some changes will need to be made in present natural gas technology, but they are modest (for example, methane used for fuel cells cannot have traces of methanethiol or ethanethiol, the smelly chemicals injected into natural gas distributions to help users find leaks, because the sulfur component of the odorant destroys the fuel cell membrane catalysts).

It should be noted that the methane fuel cell car faces competition from direct methane-burning cars. Since the technology for running internal combustion engines directly from compressed methane is well developed, relatively low polluting (in terms of gases other than CO2), is about equally energy efficient to methane fuel cells, with excellent engine life, it appears likely that for the near term, compressed methane or compressed natural gas (CNG) will be used in this simple manner for transportation energy, if it is to be used at all.

Problems in implementation

Production

Main article: Hydrogen production

Pure hydrogen is not widely available on our planet. Most of it is locked in water or hydrocarbon fuels. Hydrogen can be produced using other high-energy fuels, i.e. fossil fuels, but such methods generate CO2 to a greater extent than conventional internal combustion engines and thus contribute to global warming more than if those fossil fuels were used directly to power automobiles. It can also be produced using huge amounts of energy and water in the form of electrolysis. Nuclear power can provide the energy, but has its disadvantages. Solar power has also been considered, but is location dependant.

Moreover, most 'green' sources produce rather low-intensity energy (which can be scaled up, albeit at a slight efficiency cost), not the prodigious amounts of energy required for extracting significant amounts of hydrogen, like high-temperature electrolysis (could use solar concentrators for heat).

There is concern about the energy-consuming process of manufacturing the hydrogen. Manufacturing hydrogen requires a hydrogen carrier such as a fossil fuel or water. The former consumes the fossil resource and produces carbon dioxide, while electrolyzing water requires electricity, which is mostly generated at present using conventional fuels (fossil fuel or nuclear power). While alternative energy sources like wind and solar power could also be used, they are still more expensive given current prices of fossil fuels and nuclear energy. In this regard, hydrogen fuel technology itself cannot be called truly independent of fossil fuel dependence (or completely non-polluting), unless a totally nuclear or renewable energy option were considered.

Electrolysis

When the energy supply is chemical, it will always be more efficient to produce hydrogen through a direct chemical path. But when the energy supply is mechanical (hydropower or wind turbines), hydrogen can be made via electrolysis of water. Usually, the electricity consumed is more valuable than the hydrogen produced, which is why only a tiny fraction of hydrogen is currently produced this way.

When the energy supply is in the form of heat (solar thermal or nuclear), the only existing path to hydrogen is currently through high-temperature electrolysis. In contrast with low-temperature electrolysis, high-temperature electrolysis (HTE) electrolysis of water converts more of the initial heat energy into chemical energy (hydrogen), potentially doubling efficiency, to about 50%. Because some of the energy in HTE is supplied in the form of heat, less of the energy must be converted twice (from heat to electricity, and then to chemical form), and so less energy is lost. HTE has been demonstrated in a laboratory, but not at a commercial scale.

High-temperature electrolysis (HTE)

HTE processes are generally only considered in combination with a nuclear heat source, because the other non-chemical form of high-temperature heat (concentrating solar thermal) is not consistent enough to bring down the capital costs of the HTE equipment. The hydrogen nuclear proposal looks even better considering that hydrogen doesn't transmit radiation, it could be used as a coolant, replacing the dangerously radioactive cooling water. Research into HTE and high-temperature nuclear reactors may eventually lead to a hydrogen supply that is cost-competitive with natural gas steam reforming.

Some prototype Generation IV reactors operate at 850 to 1000 degrees Celsius, considerably hotter than existing commercial nuclear power plants. General Atomics predicts that hydrogen produced in a High Temperature Gas Cooled Reactor (HTGR) would cost $1.53/kg. In 2003, steam reforming of natural gas yielded hydrogen at $1.40/kg. At 2005 gas prices, hydrogen cost $2.70/kg. Hence, just within the United States, a savings of tens of billions of dollars per year is possible with a nuclear-powered supply. Much of this savings would translate into reduced oil and natural gas imports.

One side benefit of a nuclear reactor that produces both electricity and hydrogen is that it can shift production between the two. For instance, the plant might produce electricity during the day and hydrogen at night, matching its electrical generation profile to the daily variation in demand. If the hydrogen can be produced economically, this scheme would compete favorably with existing grid energy storage schemes. What is more, there is sufficient hydrogen demand in the United States that all daily peak generation could be handled by such plants.

Thermochemical production

Some thermochemical processes, such as the sulfur-iodine cycle, can produce hydrogen and oxygen from water and heat without using electricity. Since all the input energy for such processes is heat, they can be more efficient than high-temperature electrolysis. Thermochemical production of hydrogen using chemical energy from coal or natural gas is generally not considered, because the direct chemical path is more efficient.

None of the thermochemical hydrogen production processes have been demonstrated at production levels, although several have been demonstrated in laboratories.

Hydrogen fuel cell problem

The physical laws relating to the conservation of energy unfortunately create a situation where the energy needed to create the fuel in the first place may reduce the ultimate energy efficiency of the system to below that of the most efficient gasoline internal-combustion engines; this is especially true if the hydrogen has to be compressed to high pressures or liquified, as it does in automobile applications (the electrolysis of water is itself a rather inefficient process, usually requiring at least 50% more electricity than the energy stored in the produced hydrogen). However, even the most efficient internal-combustion engines are not very efficient in absolute terms; furthermore, gasoline is not a primary energy source, because crude oil has to be treated in a refinery to obtain gasoline.

More over, the inefficiencies in the three stages: electrolysis, transportation and/or storage, and oxidation, necessitates the production of additional electricity, creating additional pollution, worsening the problem the hydrogen fuel cells were meant to alleviate. Other fuel cell technologies based on the exchange of metal ions (i.e. zinc-air fuel cells) are typically more efficient at energy conversion than hydrogen fuel cells, but the widespread use of any electrical energy->chemical energy->electrical energy systems would necessitate the production of more electricity.

In summary, the so-called the production problem is seen to be a combination of two different problems: one of producing hydrogen efficiently from energy sources, and the other of locating suitable (renewable or at least less polluting) energy sources to do it.

Storage

Main article: Hydrogen storage

Although Hydrogen gas has good energy density per weight, it has a poor energy density per volume. Hence it requires a large tank to store it. Increasing gas pressure would improve the energy density per volume, making for smaller, but not lighter container tanks (see pressure vessel). Compressing a gas will require energy to power the compressor. Higher compression will mean more energy lost to the compression step, and it compounds safety issues as well as adding weight. Alternatively, higher volumetric energy density liquid hydrogen may be used. However liquid hydrogen is cryogenic and boils around 20.268 K (–252.882 °C or -423.188 °F). Hence its liquefaction imposes a large energy loss, used to cool it down to that temperature. The tanks must also be well insulated to prevent boil off. Ice may form around the tank and help corrode it further if the insulation fails. Insulation for liquid hydrogen tanks is usually expensive and delicate.

Cryogenic storage cuts weight but requires large liquification energies and the liquid hydrogen product still does not have impressive energy density per volume (though it is attractive per mass). Even liquid hydrogen has worse energy density per volume than hydrocarbon fuels such as gasoline by approximately a factor of four.

The large tanks needed for uncompressed hydrogen reduces the fuel efficiency of the vehicle. Because it is a small energetic molecule, hydrogen tends to diffuse through any liner material intended to contain it, leading to the embrittlement, or weakening of its container. This is called the storage problem.

The most common way to store hydrogen is to compress it to around 700 bar (70 MPa). Many people believe that the energy needed to compress the gas is one of the major faults in the idea of a hydrogen based economy. For example, if one considers the entire world using hydrogen just in their cars, then a massive amount of energy would be needed to be compressed and stored. Thus, if it were not used in any way, the net energy used to compress it would be wasted. These types of fuel cells are very expensive, typically 100 times more expensive per kW output than conventional internal combustion engines. It has further been suggested that cars powered by Li-on or Li-polymer batteries are capable of being more efficient than hydrogen-based cars would ever be, and that they just need to be mass produced to become cost effective. There are also prototype designs for zinc-air fuel cells, which can function as large, rechargeable batteries, and are as efficient as any battery based system, but with ranges around 400 to 500 miles, instead of 70. For long trips, the electrolyte can even be completely replaced/exchanged at filling stations, which then recharge and recycle the spent electrolyte.

Transmission

It is not clear if hydrogen can be put into today's natural gas transmission systems. Proponents of the hydrogen economy envision local hydrogen sources. The challenges that large, rural high-efficiency hydrogen generators face are far more acute in an urban environment. Thus, some kind of transmission system will probably be required for cities.

Hydrogen use would require the alteration of industry and transport on a scale never seen before in history. For example, the distributing hydrogen fuel for vehicles will require an entirely new infrastructure which, just in the U.S., would cost hundreds of billions, or even trillions, of dollars. However, economic incentives, future oil factor of production costs, poor alternatives and better technology are seen as making the transition economically viable in the future.

Cost

Hydrogen seems unlikely to be the cheapest carrier of energy over long distances in the near future. Advances in electrolysis and fuel cell technology have not addressed the underlying cost problem yet.

Hydrogen pipelines are unfortunately more expensive than even long-distance electric lines. Hydrogen is about three times bulkier in volume than natural gas for the same energy delivered, and hydrogen accelerates the cracking of steel (hydrogen embrittlement), which increases maintenance costs, leakage rates, and material costs. The difference in cost is likely to expand with newer technology: wires suspended in air can utilize higher voltage with only marginally increased material costs, but higher pressure pipes require proportionally more material.

Setting up a hydrogen economy would require huge investments in the infrastructure to store and distrubute hydrogen to vehicles, in addition to the cost of the new vehicles themselves. In contrast, electric vehicles using batteries, which are currently at a similar stage of technological maturity, don't require infrastructure investments. Since hydrogen is likely to be produced with the same sources as electricity (fossil, nuclear, solar, wind) it may be less economical than a pure electricity economy. See The Hype about Hydrogen.

Alternatives to the hydrogen economy

Hydrogen is simply a method to store and transmit energy. Various alternative energy transmission and storage scenarios may be more economic, in both near and far term. These include:

  • Natural gas. The move away from dwindling oil supplies to other forms of fossil fuel such as natural gas and liquified natural gas has begun. This movement is becoming more popular, especially as large methane reserves may be available in deep ocean beds and, in some industrialized countries, especially the U.S., where there are large reserves of natural gas. Methane can be made from coal through several steps, but doing so increases air pollution. A drawback is that coal and natural gas, like oil, will eventually run out.
  • The electrical grid plus batteries. The electrical grid and chemical storage battery pose viable long term alternatives to hydrogen in transmission, especially as more large batteries are made available on the grid in the form of electric or hybrid autos, which might act as load-balancers. The solar cell might also be used in some areas to make energy locally for battery powered autos. Of these technologies, only grid power is currently in a high state of technical development. Solar power suffers from a low power density to area, making it difficult to use in transport. High capacity batteries (chemical cells) have already seen use in commercial hybrid cars, but these have yet to be used in load-balancing. It is possible that a combination of battery and hydrogen power will be used in the future, although many think that hybrid cars running on battery power and green fuels is a more viable option.

Other chemical fuels:

Main article: Alternative fuel
  • Green fuels. Alternatives such as plant produced Bio-fuels (Ethanol, Biodiesel) would require smaller changes to the economy but are not viable in most countries because a large amount of cultivated land would be needed to produce enough bio-fuels to replace a large enough proportion of petroleum. Hybrid vehicles using a combination of battery power (derived from nuclear or renewable sources) and green fuels, however, could significantly reduce the total demand for the green fuels needed to replace existing petroleum demand.
  • Hydrogen production of greenhouse-neutral alcohol. Hydrogen in a full "hydrogen economy" has been envisioned as a way to make renewable energy available to automobiles which are not all-electric. A final theoretical alternative to hydrogen would do this by using hydrogen locally to make other liquid fuels, which then act as energy stores and carriers but without disrupting present methods of liquid fuel transport and use. Rather than be transported from its production site, hydrogen may instead be used centrally to produce renewable liquid fuels which may be cycled into the present transportation infrastructure directly.

Environmental concerns

Hydrogen gas can be created through the natural gas steam reforming/water gas shift reaction method, outlined above. This creates carbon dioxide (CO2), a greenhouse gas, as a byproduct. This is usually released into the atmosphere, although there has also been some research into interring it underground or undersea. The steam reformers in methane-based fuel cells convert hydrocarbons into either carbon dioxide or carbon monoxide (CO). [1]

Recently, there have also been some concerns over possible problems related to hydrogen gas leakage, (this has been pointed out in a paper published in Science magazine by a group of Caltech scientists). Molecular hydrogen leaks slowly from most containment vessels. It has been hypothesized that if significant amounts of hydrogen gas (H2) escape, hydrogen gas may, due to ultraviolet radiation, form free radicals (H) in the stratosphere. These free radicals would then be able to act as catalysts for ozone depletion. A large enough increase in stratospheric hydrogen from leaked H2 could exacerbate the depletion process. However, the effect of these leakage problems may not be significant. The amount of hydrogen that leaks today is much lower (by a factor of 10-100) than the estimated 10%-20% figure conjectured by some researchers; in Germany, for example, the leakage rate is only 0.1% (less than the natural gas leak rate of 0.7%). At most, such leakage would likely be no more than 1-2% even with widespread hydrogen use, using present technology. Additionally, present estimates indicate that it would take at least 50 years for a mature hydrogen economy to develop, and new technology developed in this period could further reduce the leakage rate.

Direct dangers in use

Hydrogen has been feared in the popular press as a relatively more dangerous fuel, and hydrogen in fact has a wider explosive/ignition mix range with air of all the gases. Hydrogen also usually rapidly escapes after containment breach. Additionally, hydrogen flames are difficult to see, so may be difficult to fight. Most of these problems are offset in reality by the fact that hydrogen rapidly disperses by lifting off the scene due to buoyancy, and this is true to some extent of hydrogen fires. For example, it is often forgotten that in the most famous hydrogen fire, the LZ 129 Hindenburg disaster, 2/3 of passengers and crew survived (most deaths were from jumping). Even with similar behavior, this survival fraction would seem most unlikely in a similar conflagration produced by an equal energy-equivalent of aviation fuel.

Examples and Pilot Programs

Several domestic U.S. automobile manufactures have committed to develop vehicles using hydrogen. (They had previously committed to producing electric vehicles in California, a program now defunct at their behest.) Critics argue this "commitment" is merely a ploy to sidestep calls for increased efficiency in gasoline and diesel fuel powered vehicles and diverts us from needed steps to address global warming, such as greater focus on conservation, green fuel production and other green technologies. The distribution of hydrogen for the purpose of transportation is currently being tested in very limited markets around the world, particularly in Iceland, Germany, California, Japan and Canada, but the cost is very high.

Some hospitals have installed combined electrolyzer-storage-fuel cell units for local emergency power. These are advantageous for emergency use due to their low maintenance requirement and ease of location compared to internal combustion driven generators.

The North Atlantic island country of Iceland has committed to becoming the world's first hydrogen economy by the year 2050. Iceland is in a unique position: at present, it imports all the petroleum products necessary to power its automobiles and fishing fleet. But Iceland has large geothermal and hydroelectric resources, so much so that the local price of electricity actually is lower than the price of the hydrocarbons that could be used to produce that electricity.

Iceland already converts its surplus electricity into exportable goods and hydrocarbon replacements. In 2002, it produced 2000 tons of hydrogen gas by electrolysis, primarily for the production of ammonia (NH3) for fertilizer. Ammonia is produced, transported, and used throughout the world, and 90% of the cost of ammonia is the cost of the energy to produce it. Iceland is also developing an aluminum-smelting industry - aluminum costs are primarily driven by the cost of the electricity to run the smelters. Either of these industries could effectively export all of Iceland's potential geothermal electricity.

But neither directly replaces hydrocarbons. Reykjavík has a small pilot fleet of city busses running on compressed hydrogen [2], and research on powering the nation's fishing fleet with hydrogen is underway. For practicality, Iceland may end up processing imported oil with hydrogen to extend it, rather than to replace it altogether.

A pilot project demonstrating a hydrogen economy is operational on the Norwegian island of Utsira. The installation combines wind power and hydrogen power. In periods when there is surplus wind energy, the excess power is used for generating hydrogen by electrolysis. The hydrogen is stored, and is available for power generation in periods where there is little wind.

The UK completed a fuel cell pilot program in December 2005. Started in January 2004, the program ran two Fuelcell busses on route 25 in London.

The Hydrogen Expedition is currently working on creating a hydrogen fuel cell-powered ship and using it to circumnavigate the globe, as a way to demonstrate the capability of hydrogen fuel cells.

Western Australia's Department of Planning and Infrastructure currently operates three Daimler Chrysler Citaro fuel cell buses as part of its Sustainable Transport Energy for Perth Fuel Cells Bus Trial in Perth. The buses are operated by Path Transit on regular Transperth public bus routes. The trial began in September 2004 and will conclude in September 2006. The buses' fuel cells use a proton exchange membrane system and are supplied with raw hydrogen from a BP refinery in Kwinana, south of Perth. The hydrogen is a byproduct of the refinery's industrial process. The buses are refuelled at a station in the northern Perth suburb of Malaga.

Conclusion

Before the technical and economic challenges of implementing a "hydrogen economy" can be fully addressed, the fundamental problem of renewable energy production requires a solution. Even then, there are many problems to be solved before hydrogen can serve as a universal energy medium. These include difficulties with hydrogen production, transportation, storage, distribution and end use. It will take many decades to solve all of these problems, and hydrogen may never be the most economically feasible energy storage medium for most uses.

References

  • Jeremy Rifkin (2002). The Hydrogen Economy. Penguin Putnam Inc. ISBN 1585421936.
  • Roy McAlister (2003). The Solar Hydrogen Civilization. American Hydrogen Association. ISBN 0-9728375-0-7.
  • Joseph J. Romm (2004). The Hype about Hydrogen, Fact and Fiction in the Race to Save the Climate. Island Press. ISBN 155963703X. Author interview at Global Public Media.
  • James Howare Kunstler (2006). The LONG EMERGENCY. Grove Press. ISBN 0802142494. Hydrogen economy = "laughable a fantasy" p. 115

See also

Template:Sustainability and energy development group

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