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A hydrogen economy is a hypothetical Economy in which the Energy needed for motive power (for automoblies or other vehicle types) or electricity (for stationary applications) is derived from reacting Hydrogen (H2) with oxygen. While the primary purpose is to provide an energy carrier to replace dwindling supplies of Petroleum , a secondary goal is to eliminate the use of carbon-based Fossil Fuel s and thus reduce Carbon Dioxide emissions. In the context of a hydrogen economy, hydrogen is an energy storage medium, not a primary energy source (see Nuclear Fusion for an entirely separate discussion of using hydrogen as an atomic energy source). Nevertheless, controversy over the usefulness of a hydrogen economy have 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 impacts them all (see below). Proponents of a hydrogen economy suggest that hydrogen is 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. Analyses have concluded 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 are utilized at the site of energy or hydrogen production.http://www.nap.edu/openbook.php?isbn=0309091632 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 Cell s, or production of liquid Synthetic Fuel s from 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). Hydrogen cars may be a long time coming 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".http://www.nap.edu/openbook.php?isbn=0309091632 RATIONALE A hydrogen economy is proposed to solve the ill effects of using Hydrocarbon fuels in transportation, and other end-use applications where the carbon is released to the atmosphere. In the current economy, the Transportation of people and goods (so-called ''mobile applications'') is Fuel ed 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, and the demand for hydrocarbon fuels is increasing, particularly in China, India and other developing countries. In a hydrogen economy, hydrogen fuel would be manufactured from some primary energy source and used as a replacement for hydrocarbon-based fuels for transport. The hydrogen would be utilized either by direct combustion in Internal Combustion Engines or as fuel in proton exchange membrane Fuel Cells . The primary energy source can then become a stationary plant which can use Renewable , Nuclear or Coal -fired energy sources, easing the pressure on finite liquid and gas hydrocarbon resources. There is no carbon dioxide emission at the point of use. With suitable primary energy sources, Greenhouse Gas emissions can be reduced or eliminated. Excepting minor NOx generation from hydrogen internal combustion engines, the emission footprint of a hydrogen economy remains that of the underlying energy generation technology. Hydrogen has a high Energy Density by Weight . 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 35-45% efficient (some even higher) (not accounting for losses in the actual production of hydrogen, which would result in an overall efficiency of about 25%) and together with the electric motor and controller, the drive train overall efficiency approaches 24% with low idling losses. PERSPECTIVE: CURRENT HYDROGEN MARKET (CURRENT HYDROGEN ECONOMY) Hydrogen production is a large and growing industry. Globally, some 50 million Metric Ton s 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 ( N H3) 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 Sand s 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 (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 http://www.dis.anl.gov/ceeesa/documents/NuclearHydrogen_ANL0530Final.pdf, 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 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 have also stimulated great interest in alternate, cheaper means of hydrogen production. http://www.dis.anl.gov/ceeesa/programs/hydrogen_markets.html PRODUCTION, STORAGE, DISTRIBUTION See Also: Hydrogen technologies 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. 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 renewables) can be used. 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. Methods of production See Also: Hydrogen production Molecular hydrogen is not available on Earth in convenient natural reservoirs, though it is an atmospheric trace gas having a , published 2005-01-14, accessed 2007-05-14 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 ). The Economics and Environmental impact of any implementation of any future hydrogen economy will largely be determined by Future Energy Development . 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 Electrolysis of Water . In current market conditions, the 50 kWh of electricity consumed to manufacture one kilogram of 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 any source other than fossil fuels if it is to achieve the goals which primarily drive it. High-temperature electrolysis (HTE) 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. HTE has been demonstrated in a laboratory, but not at a commercial scale. HTE processes are generally only considered in combination with a nuclear heat source, because the only 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. 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 Reactor s 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. Hence, just within the United States, a savings of tens of billions of dollars per year is possible with a nuclear-powered hydrogen supply of this type. Much of this saving 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, and offloading the extra output at night into a storable medium for energy. If hydrogen can be produced economically, this scheme would compete favorably with existing Grid Energy Storage schemes for electrical power. There is sufficient hydrogen demand in the United States that all daily peak generation could potentially be handled by such plants, with their excess generation converted to hydrogen at other times. Thermochemical production Some thermochemical processes, such as the Sulfur-iodine Cycle , can produce hydrogen and oxygen from water and heat without using electricity. These processes 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. Passive Production Researchers at Purdue University have further developed a technology to create hydrogen gas passively without input power. The new process involves running water across an aluminum/gallium alloy. This new process will be presented on September 7, 2007 at the Second Energy Nanotechnology International Conference. Childhood dreams may soon come true: Engines that run on water Storage See Also: Hydrogen 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 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, in part 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). Storage tanks must also be well insulated to minimize 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. 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 , Nanostructure d 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 ). Many people believe that the energy needed to compress hydrogen to these pressures presents a major barrier to a hydrogen economy. For example, if one considers the entire world using hydrogen just in their cars, then a large amount of energy would be needed simply to compress the hydrogen for storage, of the order of 30% of the total energy used for transport. If this energy was not recovered in any way, the net energy used to compress it would be wasted. Currently, vehicle fuel cells are very expensive, typically 100 times more expensive per kW output than conventional internal combustion engines. It further has been suggested that cars utilizing Li-ion or Li-polymer Batteries for onboard energy storage are capable of being more efficient than hydrogen-fueled 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 . For long trips, the electrolyte can even be completely replaced/exchanged at filling stations, which then recharge and recycle the spent electrolyte. Distribution 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. 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 (Kreith, 2004). 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. 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, which is roughly 70 percent efficient (using the lower heating value for hydrogen). 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" (Nakicenovic, 1998).) 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 See Also: Fuel cell One of the main offerings of a hydrogen economy is that fuel cells can replace Internal Combustion Engine s and Turbine s 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 commercialisation 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 Car s. 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 engineerable 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 Tax es. INFRASTRUCTURE Since hydrogen causes Hydrogen Embrittlement of steel, it is not clear if hydrogen can simply 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 distribution of hydrogen fuel for vehicles in the U.S. would require an entirely new infrastructure costing hundreds of billions of dollars, or more. Costs Hydrogen seems unlikely to be the cheapest carrier of energy over long distances. Advances in electrolysis and fuel cell technology have not addressed the underlying cost problem. Hydrogen pipelines are more expensive http://www.ef.org/documents/NDakotaWindPower.pdf 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. Similarly, Battery Electric Vehicle s, which are in the demonstration phase, would necessitate expansion of existing infrastructure for electricity transmission and distribution if such vehicles were placed in widespread service on the order of 100 million 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. Some facts and figures have recently been suggested by the magazine ''Popular Mechanics'' (November, 2006): ;Natural Gas at Small Scale: Uses steam reformation. Requires 15.9 Million cubic feet of gas, which, if produced by small 500kg/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 km&2) 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.
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: ;Compressed air: 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). ;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. http://www.memagazine.org/contents/current/webonly/webex710.html http://www.energy.iastate.edu/becon/ammonia.html ;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 is 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. Thus, over the long term, the cost of energy storage in batteries is driven largely by the high cost of the replacement of batteries themselves, not the cost of the energy which is temporarily stored in them over their lives. Presently, the cost of storing energy for any extended length of time is prohibitive when using the present generation of batteries, even when compared with hydrogen storage. This may change as battery technology improves. Nimh batteries have been shown to have a much longer lifetime, although they eventually self-discharge and can not be used for long term storage. Some of these problems are addressed in the ''artificial'' production of hydrocarbon fuels from hydrogen (see below), which (as envisioned) do not require the intermediary of green plants. 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 technolgies. 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 and 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 .
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REFERENCES http://www.popularmechanics.com/technology/industry/4199381.html?page=3 http://www.tgdaily.com/content/view/33570/113/ FURTHER READING
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