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Hydrogen economy
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The hydrogen economy is a proposed system of meeting energy needs by using hydrogen as a fuel source that could be generated from alternative fuels or other energy sources that don't give off greenhouse gases. Hydrogen (H2) gives off energy when it is combined with oxygen, but the hydrogen itself has to first be produced, which requires more energy than is released when it is used as a fuel.
To gather hydrogen as a fuel, it first has to be generated by electrolysis of water or another method.
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Encyclopedia
The hydrogen economy is a proposed system of meeting energy needs by using hydrogen as a fuel source that could be generated from alternative fuels or other energy sources that don't give off greenhouse gases. Hydrogen (H2) gives off energy when it is combined with oxygen, but the hydrogen itself has to first be produced, which requires more energy than is released when it is used as a fuel.
To gather hydrogen as a fuel, it first has to be generated by electrolysis of water or another method. A reduction in Carbon dioxide emission would only be achieved if the energy used to split the water is obtained from non carbon-based sources because the hydrogen fuel has to first be made with a substantial input of energy from another fuel source.
Some futurists promote hydrogen as potential fuel for motive power (including cars, boats and airplanes), the energy needs of buildings and portable electronics. They believe a hydrogen economy could greatly reduce the emission of carbon dioxide and therefore play a major role in tackling global warming. Countries without oil, but with renewable energy resources, could use a combination of renewable energy and hydrogen instead of fuels derived from petroleum, which are becoming scarcer, to achieve energy independence.
In the context of a hydrogen economy, hydrogen is an energy carrier, not a primary energy source (see nuclear fusion for an entirely separate discussion of using hydrogen isotopes as an atomic energy source). Nevertheless, controversy over the usefulness of a hydrogen economy has been confused by issues of energy sourcing, including fossil fuel use, global warming, and sustainable energy generation. These are all separate issues, although the hydrogen economy affects them all (see below).
Proponents of a world-scale hydrogen economy argue that hydrogen can be an environmentally cleaner source of energy to end-users, particularly in transportation applications, without release of pollutants (such as particulate matter) or greenhouse gases at the point of end use. A 2004 analysis asserted that "most of the hydrogen supply chain pathways would release significantly less carbon dioxide into the atmosphere than would gasoline used in hybrid electric vehicles" and that significant reductions in carbon dioxide emissions would be possible if carbon capture or carbon sequestration methods were utilized at the site of energy or hydrogen production.
Critics of a hydrogen economy argue that for many planned applications of hydrogen, direct distribution and use of energy in the form of electricity, or alternate means of storage such as chemical batteries, fuel plus fuel cells, or production of liquid synthetic fuels from locally-produced hydrogen and CO2 (see methanol economy), might accomplish many of the same net goals of a hydrogen economy while requiring only a small fraction of the investment in new infrastructure. Hydrogen has been called the least efficient and most expensive possible replacement for gasoline (petrol) in terms of reducing greenhouse gases. A comprehensive study of hydrogen in transportation applications has found that "there are major hurdles on the path to achieving the vision of the hydrogen economy; the path will not be simple or straightforward". 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".
Recent publicly describing the use of low cost materials and manufacturing processes challenge the popular critique. Hydrogen (renewable hydrogen) can be produced from renewable sources, thus enabling the intermittent and excess power generated to be stored for applications in transport, homes and businesses, thereby making off-grid wind and solar sources economic.
The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors (GM) Technical Center.
Rationale
A hydrogen economy is proposed to solve some of the negative effects of using hydrocarbon fuels in transportation, and other end-use applications where the carbon is released to the atmosphere. Modern interest in the hydrogen economy can generally be traced to a 1970 technical report by Lawrence W. Jones of the University of Michigan.
In the current hydrocarbon economy, the transportation of people and goods (so-called mobile applications) is fueled primarily by petroleum, refined into gasoline and diesel, and natural gas. However, the burning of these hydrocarbon fuels causes the emission of greenhouse gases and other pollutants. Furthermore, the supply of hydrocarbon resources in the world is limited due to their inherent nature, and the demand for hydrocarbon fuels is increasing, particularly in China, India and other developing countries.
Hydrogen has a high energy density by weight. The fuel cell is also more technically but not economically efficient than an internal combustion engine. The hydrogen internal combustion engine is said to be about 38% efficient, 8% higher than gasoline internal combustion engine, while the fuel cell is 2-3 times more efficient than an internal combustion engine. However, the high capital cost of fuel cell, about $5,500/kW, is one of the major obstacles of its development that is needed to be overcome before commercialization. Other technical obstacles of fuel cells include the purity requirement of hydrogen; with current technology, an operating fuel cell requires the purity of hydrogen to be as high as 99.999%. On the other hand, hydrogen engine conversion technology is more economical than fuel cells.
Perspective: current hydrogen market (current hydrogen economy)
Hydrogen production is a large and growing industry. Globally, some 50 million metric tons of hydrogen, equal to about 170 million tons of oil equivalent, were produced in 2004. The growth rate is around 10% per year. Within the United States, 2004 production was about 11 million metric tons (MMT), an average power flow of 48 gigawatts. (For comparison, the average electric production in 2003 was some 442 gigawatts.) As of 2005, the economic value of all hydrogen produced worldwide 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 both the world population and the intensive agriculture used to support it are 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. The scale economies inherent in large scale oil refining and fertilizer manufacture make possible on-site production and "captive" use. Smaller quantities of "merchant" hydrogen are manufactured and delivered to end users as well.
If energy for hydrogen production were available (from wind, solar or nuclear power), use of the substance for hydrocarbon synfuel production could expand captive use of hydrogen by a factor of 5 to 10. Present U.S. use of hydrogen for hydrocracking is roughly 4 million metric tons per year (4 MMT/yr). It is estimated that 37.7 MMT/yr of hydrogen would be sufficient to convert enough domestic coal to liquid fuels to end U.S. dependence on foreign oil importation, and less than half this figure to end dependence on Middle East oil. Coal liquefaction would present significantly worse emissions of carbon dioxide than does the current system of burning fossil petroleum, but it would eliminate the political and economic vulnerabilities inherent in oil importation.
Currently, global hydrogen production is 48% from natural gas, 30% from oil, and 18% from coal; water electrolysis accounts for only 4%. The distribution of production reflects the effects of thermodynamic constraints on economic choices: of the four methods for obtaining hydrogen, partial combustion of natural gas in a NGCC (natural gas combined cycle) power plant offers the most efficient chemical pathway and the greatest off-take of usable heat energy.
The large market and sharply rising prices in fossil fuels have also stimulated great interest in alternate, cheaper means of hydrogen production. Currently, most hydrogen are produced on site and the cost is approximately 0.32/lb and, if not produced on site, the cost of liquid hydrogen is about 1.00/lb to 1.40/lb.
Production, storage, infrastructure
Today hydrogen is produced for merchant use and captive industrial applications using mature, thermodynamically efficient technologies. Linking its centralized production to a fleet of light-duty fuel cell vehicles will require the siting and construction of a distribution infrastructure with large investment of capital. Further, the technological challenge of providing safe, energy-dense storage of hydrogen on-board the vehicle must be overcome to provide sufficient range between fillups.
Methods of production
Molecular hydrogen is not available on Earth in convenient natural reservoirs, though it is an atmospheric trace gas having a mixing ratio of 500 parts per billion by volume in addition to being produced by microbes and consumed by methanogens in a rapid biological hydrogen cycle. Most hydrogen on Earth is bonded to oxygen in water. Hydrogen is presently most economically produced using fossil fuels. In practice this is usually methane, though hydrogen can also be produced via steam reforming or partial oxidation of coal. It can also be produced via electrolysis using electricity and water, consuming approximately 50 kilowatt-hours of electricity per kilogram of hydrogen produced. Though the use of platinum as a catalyst for electrolytic separation of H2O into hydrogen and oxygen is well-known, some companies have now found ways to make fuel cells without platinum which can reduce the cost of this expensive element which can account for approximately 60% of the cost of the fuel cell. Nuclear power can provide the energy for hydrogen production by a variety of means, but its widescale deployment is opposed in some Western economies while it is embraced in others. Renewable energy is being used to produce hydrogen in Denmark and Iceland.
The environmental effects of hydrogen production can be compared with alternatives, taking into account not only the emissions and efficiency of the hydrogen production process but also the efficiency of the hydrogen conversion to electricity in a fuel cell.
While hydrogen (the element) is abundant on Earth, and indeed is the most abundant element in the universe, manufacturing hydrogen does require the consumption of a hydrogen carrier such as a fossil fuel or water. The former consumes the fossil resource and produces carbon dioxide, but often requires no further energy input beyond the fossil fuel. Decomposing water requires electrical or heat input, generated from some primary energy source (fossil fuel, nuclear power or a renewable energy).
Kværner-process
The Kværner-process or Kvaerner carbon black & hydrogen process (CB&H) is a method, developed in the 1980s by a Norwegian company of the same name, for the production of steam from hydrocarbons (CnHm), such as methane, natural gas and biogas.
Of the available energy of the feed, approximately 48% is contained in the Hydrogen, 40% is contained in activated carbon and 10% in superheated steam.
Fermentative hydrogen production
Fermentative hydrogen production is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Dark fermentation reactions do not require light energy, so they are capable of constantly producing hydrogen from organic compounds throughout the day and night. Photofermentation differs from dark fermentation because it only proceeds in the presence of light. For example photo-fermentation with Rhodobacter sphaeroides SH2C can be employed to convert small molecular fatty acids into hydrogen. Electrohydrogenesis is used in microbial fuel cells.
Biological production
Biological hydrogen can be produced in an algae bioreactor. In the late 1990s it was discovered that if the algae is deprived of sulfur it will switch from the production of oxygen, i.e. normal photosynthesis, to the production of hydrogen.
It seems that the production is now economically feasible by surpassing the 7–10 percent energy efficiency (the conversion of sunlight into hydrogen) barrier.
Biological hydrogen can and is produced in bioreactors that utilize feedstocks other than algae, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and CO2. The CO2 can be sequestered successfully by several methods, leaving hydrogen gas. A prototype hydrogen bioreactor using waste as a feedstock is in operation at Welch's grape juice factory in North East, Pennsylvania.
Electrolysis
The predominant methods of hydrogen production rely on exothermic chemical reactions of fossil fuels to provide the energy needed to chemically convert feedstock into hydrogen. But when the energy supply is mechanical (hydropower or wind turbines), hydrogen can be made via high pressure electrolysis or low pressure electrolysis of water. In current market conditions, the 50 kWh of electricity consumed to manufacture one kilogram of compressed hydrogen is roughly as valuable as the hydrogen produced, assuming 8 cents/kWh. The price equivalence, despite the inefficiencies of electrical production and electrolysis, are due to the fact that most hydrogen is made from fossil fuels which couple more efficiently to producing the chemical directly, than they do to producing electricity. However, this is of no help to a hydrogen economy, which must derive hydrogen from sources other than the fossil fuels it is intended to replace.
Photoelectrochemical water splitting
Using electricity produced by photovoltaic systems offers the cleanest way to produce hydrogen. Water is broken into hydrogen and oxygen by electrolysis--a photoelectrochemical cell (PEC) process which is also named artificial photosynthesis. Research aimed toward developing higher-efficiency multijunction cell technology is underway by the photovoltaic industry.
High pressure electrolysis
High pressure electrolysis is the electrolysis of water by decomposition of water (H2O) into oxygen (O2) and hydrogen gas (H2) due to an electric current being passed through the water. The difference with an standard electrolyzer is the compressed hydrogen output around 120-200 Bar (1740-2900 psi). By pressurising the hydrogen in the electrolyser the need for an external hydrogen compressor is eliminated, the average energy consumption for internal compression is around 3%.
High-temperature electrolysis
Hydrogen can be generated from energy supplied in the form of heat (e.g., that of concentrating solar thermal or nuclear) and electricity through high-temperature electrolysis (HTE). In contrast with low-temperature electrolysis, HTE 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 potentially far less energy is required per kilogram of hydrogen produced.
Nuclear
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, and offloading the extra output at night into a storable medium for energy.
It is possible that research into HTE and high-temperature nuclear reactors may eventually lead to a hydrogen supply that is cost-competitive with natural gas steam reforming. For example, some prototype Generation IV reactors have coolant exit temperatures of 850 to 1000 degrees Celsius, considerably hotter than existing commercial nuclear power plants. High temperature (950–1000 °C) gas cooled nuclear reactors have the potential to split hydrogen from water by thermochemical means using nuclear heat. 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 natural gas prices, hydrogen costs $2.70/kg. HTE has been demonstrated in a laboratory, at 108 megajoules (thermal) per kilogram of hydrogen produced, but not at a commercial scale.The first commercial generation IV reactors are expected around 2030.
Concentrating solar thermal
The high temperatures necessary to split water can be achieved through the use of concentrating solar power. Hydrosol-2 is a 100-kilowatt pilot plant at the Plataforma Solar de Almería in Spain which uses sunlight to obtain the required 800 to 1,200 °C to split water. Hydrosol II is in operation since 2008. The design of this 100-kilowatt pilot plant is based on a modular concept. As a result, it may be possible that this technology could be readily scaled up to the megawatt range by multiplying the available reactor units and by connecting the plant to heliostat fields (fields of sun-tracking mirrors) of a suitable size.
Thermochemical production
There are more than 352 thermochemical cycles which can be used for water splitting, around a dozen of these cycles such as the iron oxide cycle, cerium(IV) oxide-cerium(III) oxide cycle, zinc zinc-oxide cycle, sulfur-iodine cycle, copper-chlorine cycle and hybrid sulfur cycle are under research and in testing phase to produce hydrogen and oxygen from water and heat without using electricity. These processes can be more efficient than high-temperature electrolysis, typical in the range from 35 % - 49 % LHV efficiency. 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.
Reactive production
Hydrogen is the product of a number of chemical reactions with metals. Sodium is a classic example, with water and sodium metal reacting to form sodium hydroxide and hydrogen. Another example which has gained some recent interest is aluminium or an aluminium/gallium alloy reacting with water to produce aluminium hydroxide and hydrogen.
In all cases the metal is consumed. The reaction product(s) (other than the hydrogen) would then be recovered for regeneration in an energy-consuming process or directly in some application.
For further details see section Chemical production in the main article:Hydrogen production
Storage
Although molecular hydrogen has very high energy density on a mass basis, due in part to its low molecular weight, as a gas at ambient conditions it has very low energy density by volume. If it is to be used as fuel stored on board the vehicle, pure hydrogen gas must be pressurized or liquefied to provide sufficient driving range. Increasing gas pressure improves the energy density by volume, making for smaller, but not lighter container tanks (see pressure vessel). Achieving higher pressures necessitates greater use of external energy to power the compression. Alternatively, higher volumetric energy density liquid hydrogen or slush hydrogen may be used. However, liquid hydrogen is cryogenic and boils at 20.268 K (–252.882 °C or –423.188 °F). Cryogenic storage cuts weight but requires large liquification energies. The liquefaction process, involving pressurizing and cooling steps, is energy intensive. The liquefied hydrogen has lower energy density by volume than gasoline by approximately a factor of four, due to the low density of liquid hydrogen — there is actually more hydrogen in a liter of gasoline (116 grams) than there is in a liter of pure liquid hydrogen (71 grams). Liquid hydrogen storage tanks must also be well insulated to minimize boil off. Ice may form around the tank and help corrode it further if the liquid hydrogen tank insulation fails.
The mass of the tanks needed for compressed hydrogen reduces the fuel economy 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.
Distinct from storing molecular hydrogen, hydrogen can be stored as a chemical hydride or in some other hydrogen-containing compound. Hydrogen gas is reacted with some other materials to produce the hydrogen storage material, which can be transported relatively easily. At the point of use the hydrogen storage material can be made to decompose, yielding hydrogen gas. As well as the mass and volume density problems associated with molecular hydrogen storage, current barriers to practical storage schemes stem from the high pressure and temperature conditions needed for hydride formation and hydrogen release. For many potential systems hydriding and dehydriding kinetics and heat management are also issues that need to be overcome.
A third approach is to absorb molecular hydrogen into a solid storage material. Unlike in the hydrides mentioned above, the hydrogen does not dissociate/recombine upon charging/discharging the storage system, and hence does not suffer from the kinetic limitations of many hydride storage systems. Hydrogen densities similar to liquefied hydrogen can be achieved with appropriate absorption media. Some suggested absorbers include MOFs, nanostructured carbons (including CNTs) and clathrate hydrate.
The most common method of on board hydrogen storage in today's demonstration vehicles is as a compressed gas at pressures of roughly 700 bar (70 MPa).
Underground hydrogen storage is the practice of hydrogen storage in underground caverns, salt domes and depleted oil and gas fields. Large quantities of gaseous hydrogen are stored in underground caverns by ICI for many years without any difficulties. The storage of large quantities of hydrogen underground can function as grid energy storage which is essential for the hydrogen economy.
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 trailers, liquid hydrogen tank trucks or dedicated onsite production.
Because of hydrogen embrittlement of steel, natural gas pipes have to be coated on the inside or new pipelines installed like the over 700 miles of hydrogen pipeline currently in the United States. Although expensive to install, once in place, pipelines are the cheapest way to move hydrogen from point A to B. This can all be avoided however with distributed hydrogen production which makes hydrogen on site with medium or small-sized generators which make enough hydrogen for an entire neighborhood or personal use. In the end, a combination of options is most likely to succeed.
While millions of tons of hydrogen are distributed all around the world each year, to bring hydrogen to individual consumers would require an evolution of the fuel infrastructure. For example, according to GM, 70% of the U.S. population lives near a hydrogen-generating facility but has little public access to that hydrogen. The same study however, shows that building the infrastructure in a systematic way is much more doable and affordable than most people think. For example, hydrogen stations could be put within every 10 miles in metro Los Angeles and on the highways between LA and neighboring cities like Palm Springs, Las Vegas, San Diego and Santa Barbara for the cost of a Starbucks latte for every one of the 15 million residents.
A key tradeoff: centralized vs. distributed production
In a future (full) hydrogen economy, primary energy sources and feedstock would be used to produce hydrogen gas as stored energy for use in various sectors of the economy. Producing hydrogen from primary energy sources other than coal, oil, and natural gas, would result in lower production of the greenhouse gases characteristic of the combustion of these fossil energy resources.
One key feature of a hydrogen economy is that in mobile applications (primarily vehicular transport) energy generation and use is decoupled. The primary energy source need no longer travel with the vehicle, as it currently does with hydrocarbon fuels. Instead of tailpipes creating dispersed emissions, the energy (and pollution) can be generated from point sources such as large-scale, centralized facilities with improved efficiency. This allows the possibility of technologies such as carbon sequestration, which are otherwise impossible for mobile applications. Alternatively, distributed energy generation schemes (such as small scale renewable energy sources) can be used, possibly associated with hydrogen stations.
Aside from the energy generation, hydrogen production could be centralized, distributed or a mixture of both. While generating hydrogen at centralized primary energy plants promises higher hydrogen production efficiency, difficulties in high-volume, long range hydrogen transportation (due to factors such as hydrogen damage and the ease of hydrogen diffusion through solid materials) makes electrical energy distribution attractive within a hydrogen economy. In such a scenario, small regional plants or even local filling stations could generate hydrogen using energy provided through the electrical distribution grid. While hydrogen generation efficiency is likely to be lower than for centralized hydrogen generation, losses in hydrogen transport can make such a scheme more efficient in terms of the primary energy used per kilogram of hydrogen delivered to the end user.
The proper balance between hydrogen distribution and long-distance electrical distribution is one of the primary questions that arises in the hydrogen economy.
Again the dilemas of production sources and transportation of hydrogen can now be overcome using on site (home, business, or fuel station) generation of hydrogen from off grid renewable sources..
Efficiency as an automotive fuel
An accounting of the energy utilized during a thermodynamic process, known as an energy balance, can be applied to automotive fuels. With today's technology, the manufacture of hydrogen via steam reforming can be accomplished with a thermal efficiency of 75 to 80 percent. Additional energy will be required to liquefy or compress the hydrogen, and to transport it to the filling station via truck or pipeline. The energy that must be utilized per kilogram to produce, transport and deliver hydrogen (i.e., its well-to-tank energy use) is approximately 50 megajoules using technology available in 2004. Subtracting this energy from the enthalpy of one kilogram of hydrogen, which is 141 megajoules, and dividing by the enthalpy, yields a thermal energy efficiency of roughly sixty percent. Gasoline, by comparison, requires less energy input, per gallon, at the refinery, and comparatively little energy is required to transport it and store it owing to its high energy density per gallon at ambient temperatures. Well-to-tank, the supply chain for gasoline is roughly 80 percent efficient (Wang, 2002). The most efficient distribution however is electrical, which is typically 95% efficient. Electric vehicles are typically 3 to 4 times as efficient as hydrogen powered vehicles.
A study of the well-to-wheels efficiency of hydrogen vehicles compared to other vehicles in the Norwegian energy system indicates that hydrogen fuel-cell vehicles tend to be about a third as efficient as EVs when electrolysis is used, with hydrogen Internal Combustion Engines (ICE) being barely a sixth as efficient. Even in the case where hydrogen fuel cells get their hydrogen from natural gas reformation rather than electrolysis, and EVs get their power from a natural gas power plant, the EVs still come out ahead 35% to 25% (and only 13% for a H2 ICE). This compares to 14% for a gasoline ICE, 27% for a gasoline ICE hybrid, and 17% for a diesel ICE, also on a well-to-wheels basis.
Distributed electrolysis
Another pathway proposed for hydrogen production is distributed electrolysis. This method would bypass the problems of distributing hydrogen somewhat by distributing electricity instead. It would take advantage of existing infrastructure to transport electricity to small, on-site electrolysers located at filling stations. Hydrogen can be produced through electrolysis of water. However, accounting for the energy used to produce the electricity (i.e., enlarging the system boundary) and accounting as well for transmission losses will reduce this efficiency.
Natural gas combined cycle power plants, which account for almost all builds of new electricity plants in the United States, generate electricity at efficiencies of 60 percent or greater. Increased demand for electricity, whether due to hydrogen cars or other demand, would have the marginal impact of adding new combined cycle power plants. On this basis, distributed production of hydrogen would be roughly 40 percent efficient. However, if the marginal impact is referred to today's power grid, with an efficiency of roughly 40 percent owing to its mix of fuels and conversion methods, the efficiency of distributed hydrogen production would be roughly 25 percent. (Note that, analogous to hydrogen production from a fossil fuel, gasoline must be refined from crude oil, the "primary energy resource".)
The distributed production of hydrogen in this fashion will be expected to generate air emissions of pollutants and carbon dioxide at various points in the supply chain, e.g., electrolysis, transportation and storage. Such externalities as pollution must be weighed against the potential advantages of a hydrogen economy. 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 electricity.
In summary, the so-called 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.
End use: fuel cells as alternative to internal combustion
One of the main offerings of a hydrogen economy is that fuel cells can replace internal combustion engines and turbines as the primary way to convert chemical energy into kinetic or electrical energy. The reason to expect this changeover is that fuel cells, being electrochemical, are usually (and theoretically) more efficient than heat engines. Currently, fuel cells are more expensive to produce than common internal combustion engines, but are becoming cheaper as new technologies and production systems develop.
Some types of fuel cells work with hydrocarbon fuels while all can be operated on pure hydrogen. In the event that fuel cells become price-competitive with internal combustion engines and turbines, large gas-fired power plants could adopt this technology. Such commercialization would be an important step in driving down the cost of fuel cell technology.
Much of the interest in the hydrogen economy concept is focused on the use of fuel cells in cars. The cells can have a superior power-to-weight ratio , are much more efficient than internal combustion engines, and produce no harmful emissions. If a practical and engineer-able method to store and carry hydrogen is introduced and fuel cells become cheaper, they can be economically viable to power hybrid fuel cell/battery vehicles, or purely fuel cell-driven ones. The economic viability of fuel cell powered vehicles will improve as the hydrocarbon fuels used in internal combustion engines become more expensive, due to the depletion of easily accessible reserves or economic accounting of environmental impact through such measures as carbon taxes.
Currently it takes 2½ times as much energy to make a hydrogen fuel cell than is obtained from it during its service life.
Hydrogen codes and standards
Hydrogen codes and standards are codes and standards for hydrogen fuel cell vehicles, stationary fuel cell applications and portable fuel cell applications.
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.
Hydrogen safety
Additional to the codes and standards (RCS) for hydrogen technology products, there are codes and standards for hydrogen safety, for the safe handling of hydrogen and the storage of hydrogen for example the Standard for the installation of stationary fuel cell power systems from the National Fire Protection Association.
Hydrogen has been feared in the popular press as a relatively more dangerous fuel, and hydrogen in fact has the widest explosive/ignition mix range with air of all the gases except acetylene. However, in actual use, the buoyancy of hydrogen helps it escape from a leak so rapidly that the dangerous situation is often mitigated before any danger can occur.. Some differences with common fuels include the fact that pure hydrogen-oxygen flames burn in the ultraviolet color range and are nearly invisible to the naked eye, thus it requires a flame detector to detect if a hydrogen leak is burning. While many characterisitcs help make hydrogen a safe fuel to handle, it is flammable and the proper following of safety guidelines is essential to ameliorate any risks just like it is for any fuel.
One of the measures on the roadmap is to implement higher safety standards like early leak detection with hydrogen sensors. The Canadian Hydrogen Safety Program concluded that hydrogen fueling is as safe as, or safer than, CNG fueling.
Environmental concerns
Hydrogen gas can be created through the natural gas steam reforming/water gas shift reaction method, which is water , with electric charge will separate into hydrogen and oxygen 2H20 ? 2H2 + O2. The energy used to create electricity which drives this reaction, originates from carbon fuels(fossil fuels) and lots of them. The reaction of a typical carbon based combustion reaction; an example of a typical combustion reaction is CH4 + 2O2 ? CO2 + 2H2O. This creates carbon dioxide (CO2), a greenhouse gas, as a byproduct, along with H2O (water). Carbon dioxide (CO2) is a gas 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).
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; for example, in Germany, 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.
Costs
When evaluating costs, Oil and Gas (fossil fuels) are generally used as the cheapest reference, even though the true cost of those fuels is seldom considered. Being fossil fuels — a non-renewable source of energy — the thousands of years required to be formed inside the Earth seem to mean "no cost" in most calculations and only the production costs are considered. Given such calculated low cost reference, any number of watts required for hydrogen production seem too much even if those watts come from a rather opposite — renewable — source of power like the Sun. Moreover, if a system for hydrogen generation and usage needs to compete with systems which use renewably generated electricity more directly, for example in trolleybuses, or in battery electric vehicles, it will always be less efficient than them due to the low efficiency of multiple conversions.
From the above, hydrogen seems unlikely to be the cheapest carrier of energy over long distances.
Demonstrated advances in electrolyzer and fuel cell technology by ITM Power are claimed to have made significant in-roads into addressing the cost of electrolysing water to make hydrogen, making cost effective production of hydrogen from off-grid renewable sources (compared to hydrocarbon fuels) possible for refueling transport and applications for short range business and residential use.
Hydrogen pipelines are more expensive than even long-distance electric lines. Hydrogen is about three times bulkier in volume than natural gas for the same enthalpy, 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 distribute hydrogen to vehicles. In contrast, battery electric vehicles, which are already publicly available, would not necessitate immediate expansion of the existing infrastructure for electricity transmission and distribution, since much of the electricity currently being generated by power plants goes unused at night when the majority of electric vehicles would be recharged. A study conducted by the Pacific Northwest National Laboratory for the US Department of Energy in December 2006 found that the idle off-peak grid capacity in the US would be sufficient to power 84% of all vehicles in the US if they all were immediately replaced with electric vehicles.
Different production methods each have differing associated investment and marginal costs. The energy and feedstock could originate from a multitude of sources i.e. natural gas, nuclear, solar, wind, biomass, coal, other fossil fuels, and geothermal.
Natural Gas at Small Scale: Uses steam reformation. Requires of gas, which, if produced by small 500 kg/day reformers at the point of dispensing (i.e., the filling station), would equate to 777,000 reformers costing $1 trillion dollars and producing 150 million tons of hydrogen gas annually. Obviates the need for distribution infrastructure dedicated to hydrogen. $3.00 per GGE (Gallons of Gasoline Equivalent)
Nuclear: Provides energy for electrolysis of water. Would require 240,000 tons of unenriched uranium — that's 2,000 600-megawatt power plants, which would cost $840 billion, or about $2.50 per GGE.
Solar: Provides energy for electrolysis of water. Would require 2,500 kWh of sun per square meter, 113 million 40-kilowatt systems, which would cost $22 trillion, or about $9.50 per GGE.
Wind: Provides energy for electrolysis of water. At 7 meters per second average wind speed, it would require 1 million 2-MW wind turbines, which would cost $3 trillion dollars, or about $3.00 per GGE.
Biomass: Gasification plants would produce gas with steam reformation. 1.5 billion tons of dry biomass, 3,300 plants which would require 113.4 million acres (460,000 km²) of farm to produce the biomass. $565 billion dollars in cast, or about $1.90 per GGE
Coal: FutureGen plants use coal gasification then steam reformation. Requires 1 billion tons of coal or about 1,000 275-megawatt plants with a cost of about $500 billion, or about $1 per GGE.
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 around the world, particularly in Portugal, Iceland, Norway, Denmark, 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. Presently, it imports all the petroleum products necessary to power its automobiles and fishing fleet. Iceland has large geothermal resources, so much 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 2,000 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 aluminium -smelting industry. Aluminium 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.
Neither industry directly replaces hydrocarbons. Reykjavík, Iceland, had a small pilot fleet of city buses running on compressed hydrogen, and research on powering the nation's fishing fleet with hydrogen is under way. For more practical purposes, Iceland might process imported oil with hydrogen to extend it, rather than to replace it altogether.
The Reykjavík buses are part of a larger program, HyFLEET:CUTE, operating hydrogen fueled buses in eight European cities. HyFLEET:CUTE buses also operate in Beijing and Perth (see below).
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 when there is little wind.
A joint venture between NREL and Xcel Energy is combining wind power and hydrogen power in the same way in Colorado.
Hydro in Newfoundland and Labrador are converting the current wind-diesel Power System on the remote island of Ramea into a Wind-Hydrogen Hybrid Power Systems facility.
A similar pilot project on Stuart Island uses solar power, instead of wind power, to generate electricity. When excess electricity is available after the batteries are full, hydrogen is generated by electrolysis and stored for later production of electricity by fuel cell.
The UK started a fuel cell pilot program in January 2004, the program ran two Fuel cell buses on route 25 in London until December 2005, and switched to route RV1 until January 2007.
The Hydrogen Expedition is currently working to create 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 concluded 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 refueled at a station in the northern Perth suburb of Malaga.
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:
Solving many of the generation, transportation and storage problems which plague hydrogen, compressed air suffers from a low energy density (energy available, per mass of necessary pressure storage tank). Compressing any gas also has to contend with inefficiencies due to heat lost in compression and decompression. See Polytropic process.
Ammonia economy
An alternative way to utilize hydrogen as an energy carrier is to bond it with the nitrogen in the air to produce ammonia which can then be easily liquefied, transported and used (directly or indirectly) as a clean and renewable fuel. The toxicity of ammonia is one of the main issues holding back an ammonia economy.
The electrical grid plus batteries
The electrical grid and chemical storage battery pose viable long term alternatives to hydrogen in transmission. The solar cell might also be used in some areas to make energy locally for battery powered autos which in turn could supply energy in the evening. 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 are a more viable option. Both the EV1 and the Rav4 EV proved the technology and were highly popular vehicles. A primary problem with lead storage batteries is that they wear out relatively quickly over time and are relatively expensive to replace. For these reasons, few new EVs prefer to use lead-acid batteries. NiMH and long-life variants of lithium-ion batteries (phosphates, titanates, spinels, etc) have been shown to have a much longer lifetime, with A123 expecting their lithium iron phosphate batteries to last for at least 10+ years and 7000+ charge cycles, and LG Chem expecting their lithium–manganese spinel batteries to last up to 40 years.
Vegetable oil
A vegetable oil economy would use green plants and sunlight to make oil from water, CO2 and macro and micro-nutrients. Vegetable oil is safer to use and store than gasoline or diesel, as it has a higher flash point. Vegetable oil works in diesel engines if it is heated first, and is easily converted to biodiesel which can directly replace diesel. Transition to vegetable oil based transportation could be gradual and relatively easy. Auto fueling stations might start with one pump for vegetable oil (as some do now for diesel) and add more, as needed. Since CO2 for this projected use is removed from the atmosphere by green plants to make the vegetable oil and then returned to the atmosphere after it is burned in an engine, there is no net increase in carbon dioxide, so this method is carbon neutral. Green plant derived oils are an example of a renewable energy store that is also safe and easy to make, store, and use. There is interest in using algaculture methods to produce vegetable oil from algae. The main drawbacks of this approach appears to be the inflationary pressure over vegetable food used to produce these oils, and competition with food crops for agricultural cropspace. The per-acre energy yield is too small to make this viable as a widespread replacement, although it is likely to maintain niche applicability for the foreseeable future.
Hydrogen production of greenhouse-neutral alcohol
This is one such artificial hydrocarbon-production plan. Hydrogen in a full "hydrogen economy" was initially suggested as a way to make renewable energy in non-polluting form, available to automobiles which are not all-electric. However, a theoretical alternative to direct elemental hydrogen use in vehicles would address the same problem by using centrally produced hydrogen immediately, to make liquid fuels from a CO2 source. Thus, hydrogen would be used captively to make fuel, and would not require expensive hydrogen transportation or storage.To be greenhouse-neutral, the source for CO2 in such a plan would need to be from air, biomass, or from CO2 which would otherwise be scheduled to be released into the air from non-carbon-capture fuel-burning power plants (of which there are likely to be many in the future, since economic carbon capture and storage is site-dependent and difficult to retrofit).
Captive hydrogen production to make more easily transportable and storable transportation fuels (such as alcohols or methane), using CO2 input, can thus be seen as the artificial, or "non-biological green" analogue of biomass, biodiesel, and vegetable oil technologies. Green plants, in a sense, already use solar power to make captively-produced hydrogen, which is then used to make easier-to-store-and-use fuels. In the plant leaf, solar energy is used to split water into hydrogen and oxygen, the latter gas being released. The hydrogen produced is then used "on-site" by the plant to reduce CO2 from the air into various fuels, such as the cellulose in wood, and the seed oils which are the basis for vegetable oil, biodiesel, etc.Hydrogen-produced alcohols would thus act as a very similar, but non-biological greenhouse-neutral way of producing energy stores and carriers from locally-produced hydrogen (solar or otherwise). By not requiring hydrogen to be produced entirely by plant leaves, they would save cropland. The fuels, however, would be used for purposes of transportation exactly as in plans to use "green fuels." Rather than be transported from its production site, hydrogen in such plans would instead be used centrally and immediately, to produce renewable liquid fuels which may be cycled into the present transportation infrastructure directly, requiring almost no infrastructure change. Moreover, methanol fuel cells are beginning to be demonstrated, so methanol may eventually compete directly with hydrogen in the fuel cell and hybrid market. See methanol economy and ethanol economy.
Captive hydrogen synthetic methane production
In a similar way as with synthetic alcohol production, hydrogen can be used on-site to directly (nonbiologically) produce greenhouse-neutral gaseous fuels. Thus, captive-hydrogen-mediated production of greenhouse-neutral methane has been proposed (note that this is the reverse of the present method of acquiring hydrogen from natural methane, but one that does not require ultimate burning and release of fossil fuel carbon). Captive hydrogen (and carbon dioxide) may be used onsite to synthesize methane, using a Sabatier reactor. This process is about 80% efficient, reducing the round trip efficiency to about 20 to 30%, depending on the method of fuel utilization. This is even lower than hydrogen, but the storage costs drop by at least a factor of 3, due to methane's higher boiling point and higher energy density. Liquid methane has 3.2 times the energy density of liquid hydrogen and is easier to store. Additionally, the pipe infrastructure (natural gas pipelines) are already in place. Natural-gas-powered vehicles already exist, and are known to be easier to adapt from existing internal engine technology, than internal combustion autos running directly on hydrogen. Experience with natural gas powered vehicles shows that methane storage is inexpensive, once one has accepted the cost of conversion to store the fuel. However, the cost of alcohol storage is even lower, so this technology would need to produce methane at a considerable savings with regard to alcohol production. Ultimate mature prices of fuels in the competing technologies are not presently known, but both are expected to offer substantial infrastructural savings over attempts to transport and use hydrogen directly.
Hybrid strategy of electricity and synthetic methanol
Electricity can be more efficiently used in a storage battery than electrolysing water to hydrogen. For example, a storage battery may retain about 90% of the electricity used to charge it, and be able to provide about 90% of the electricity that it can store, resulting in a "round trip" efficiency of about 81%. This is compared with a 70% efficiency of electrolysis and perhaps 60% efficiency of a fuel cell, resulting in a round trip efficiency of only about 40% for hydrogen — only about half the efficiency of batteries.
The electrical grid plus methanol fuel cells
Many of the hybrid strategies described above, using captive hydrogen to generate other more easily usable fuels, might be more effective than hydrogen-production alone. Short term energy storage (meaning the energy is used not long after it has been captured) may be best accomplished with battery or even ultracapacitor storage. Longer term energy storage (meaning the energy is used weeks or months after capture) may be better done with synthetic methane or alcohols, which can be stored indefinitely at relatively low cost, and even used directly in some type of fuel cells, for electric vehicles. These strategies dovetail well with the recent interest in Plug-in Hybrid Electric Vehicles, or PHEVs, which use a hybrid strategy of electrical and fuel storage for their energy needs. See plug-in hybrid electric vehicle.
Hydrogen storage has been proposed by some to be optimal in a narrow range of energy storage time, probably somewhere between a few days and a few weeks. This range is subject to further narrowing with any improvements in battery technology. It is always possible that some kind of breakthrough in hydrogen storage or generation could occur, but this is unlikely given the physical and chemical limitations of the technical choices are fairly well understood.
See also
See also alternative fuel, zinc economy, lithium economy or liquid nitrogen economy, hydrocarbon economy, low-carbon economy, wood economy.
See also
Further reading
- at Global Public Media.
- Hydrogen economy = "laughable a fantasy" p. 115
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External links
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- [ftp://ftp.cordis.europa.eu/pub/fp7/energy/docs/hydrogen_synopses_en.pdf European Projects 2002-2006 FP6]
- [https://www.hfpeurope.org/hfp/jti European Projects 2007-2013 FP7]
- - Published by the Rocky Mountain Institute, a major hydrogen economy proponent.
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- - Economic renewable hydrogen from low cost materials (non platinum, fluorocarbon free) & manufacturing processes - electrolyzers & fuel cells
- article by Robert Zubrin in The New Atlantis
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