Hydrogen economy

This article only concern with the use of hydrogen in an energy system but not any other economic system.

In a hydrogen economy or a hydrogen energy system, hydrogen, H₂, will be used as a transportation fuel via the chemical reaction H₂ + 1/2 O₂ → H₂O (water). Due to the exothermicity of this reaction, 285.77J of energy will be released from each mole of hydrogen and the energy generated by this reaction will then be converted into kinetics energy to power vehicle.

However, hydrogen, although being the simplest kind of chemical element, rarely exist by itself in nature. For example, air only contain 0.5ppmv of hydrogen. In ground state hydrogen can only be found in large quantaty in the form of water (H₂O), fossil fuel (C_mH_n) and organic chemical of many kinds. Therefore, there have been a great deal of research about the extractions of hydrogen from these three natural resources since approximately the beginning of the 20^th century. Namely, electrolysis can extract hydrogen from water by supplying electrical energy to break its chemical bond (H₂O → H₂ + 1/2O₂) and steam methane reforming can extract hydrogen from both methane (a common form of fossil fuel) and water at high temperture (CH₄ (mathane) + 2H₂O (water/ steam) → CO₂ (carbon dioxide) + 4H₂ (hydrogen)). It is important to note that there are many other methods of producing hydrogen as well but most of the are still in research state, such as direct water splitting and decarbonization of methane.

Rationale

Elements of the hydrogen economy

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 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, 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 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)

Timeline

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.

Production, storage, infrastructure

Main article: 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.

Methods of production

Main article: Hydrogen 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. More expensively 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, the actual amount of known or projected platinum in Earth would allow for less than a hundredth of a cubic centimeter for every one out of three people on Earth for private use or ownership. 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). The economics and environmental impact of any implementation of any future hydrogen economy will largely be determined by future energy development.

Biological production

Main article: Biological hydrogen production (Algae)

Biohydrogen 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 trespassing the 7–10 percent energy efficiency (the conversion of sunlight into hydrogen) barrier.

Biohydrogen 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

Electrolysis of water ship Hydrogen challenger

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 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.(The first commercial generation IV reactors are expected around 2030). In 2003, steam reforming of natural gas yielded hydrogen at $1.40/kg. At 2005 natural gas prices, hydrogen costs $2.70/kg.

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.

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.

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 (as an aluminium/gallium alloy) reacting with water to produce aluminium oxide and hydrogen. In all cases the pure metal is consumed.

Storage

Main article: 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, 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). 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.

Infrastructure

Main article: Hydrogen infrastructure

Praxair Hydrogen Plant

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, hydrogen tube trailers, liquid tankers or dedicated onsite production.

Because of hydrogen embrittlement of steel, natural gas pipes have to be coated on the inside with carbon fibers. 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, according to GM, 70% of the U.S. population lives near a hydrogen-generating facility but has just about no access to hydrogen, despite its wide availability for commercial use. The distribution of hydrogen fuel for vehicles in the U.S. would require new hydrogen stations costing 20 billion dollars. and 4.6 billion in the EU.

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.

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. 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".)

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

Main article: Fuel cell

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 it's service life.

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 millions 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 efficay of multiple conversions.

From the above, 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 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 15.9 million cubic feet (450,000 m³) 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.

• DOE Cost targets

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).

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.

Safety

The Hindenburg a few seconds after catching fire.

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. Hydrogen also usually escapes rapidly after containment breach. Additionally, hydrogen flames are difficult to see, so may be difficult to fight. An experiment performed at the University of Miami attempted to counter this by showing that hydrogen escapes while gasoline remains by setting alight hydrogen- and petrol-fuelled vehicles.

In the LZ 129 Hindenburg disaster, two thirds of the passengers and crew survived, though the skin of the Hindenburg may have contributed to the accident. It was concluded at the time by the board of enquiry that the fire was cause by electrostatic discharge of hydrogen leaking from the rear of the craft. Recent research by Addison Bain indicates that the outer fabric was highly inflammable, and that electrostatic sparks ignited the fabric first, which then spread to the hydrogen within.

In a more recent event, an explosion of compressed hydrogen during delivery at the AEP Muskingum River Coal Plant caused significant damage and killed one person.

One of the measures on the roadmap is to implement higher safety standards like early leak detection with hydrogen microsensors.

The Canadian Hydrogen Safety Program concluded that hydrogen fueling is as safe as, or safer than, CNG fueling.

Examples and pilot programs

A Mercedes-Benz O530 Citaro powered by hydrogen, in Brno.

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:

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.

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 instance, deep-discharge batteries may cost $65/KWH, and yield 400 charge-discharge cycles at 80% depth of discharge, yielding a cost of about $.20 per kwh discharged, roughly twice the average cost of US electricity.. 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.

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. Ulimate mature prices of fuels in the competing technologies are not presently known, but both are expected to offer substantial infrastructual 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, etc.

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 alternative fuel, zinc economy, lithium economy or liquid nitrogen economy, hydrocarbon economy, low-carbon economy.

See also

• Energy development
• Hydrogen vehicle
• Grid energy storage
• Hydridic Earth theory
• The Hype about Hydrogen
• Hydrogen prize
• Renewable energy in Iceland
• Renewable energy in Scotland
• Hydrogen energy plant in Denmark

Further reading

• Jeremy Rifkin (2002). The Hydrogen Economy. Penguin Putnam Inc. ISBN 1-58542-193-6.
• 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 1-55963-703-X. Author interview at Global Public Media.
• James Howare Kunstler (2006). The LONG EMERGENCY. Grove Press. ISBN 0-8021-4249-4. Hydrogen economy = "laughable a fantasy" p. 115
• M. Wang (2002). "Fuel Choices for Fuel Cell Vehicles: Well-to-Wheels Energy and Emissions Impact". Journal of Power Sources. 112: 307–321. doi:10.1016/S0378-7753(02)00447-0.
• F. Kreith (2004). "Fallacies of a Hydrogen Economy: A Critical Analysis of Hydrogen Production and Utilization". Journal of Energy Resources Technology. 126: 249–257. doi:10.1115/1.1834851.
• Nakicenovic; et al. (1998). Global Energy Perspectives. Cambridge University Press. {{cite book}}: Explicit use of et al. in: |author= (help) Summary
• National Research Council (2004). The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs. National Academy Press.
• Novelli, P.C., P.M. Lang, K.A. Masarie, D.F. Hurst, R. Myers, and J.W. Elkins. (1999). "Molecular Hydrogen in the troposphere: Global distribution and budget". J. Geophys. Res. 104(30): 427–30.{{cite journal}}: CS1 maint: multiple names: authors list (link)
• T. K. Tromp (2003). "Potential Environmental Impact of a Hydrogen Economy on the Stratosphere". Science. 300: 1740–1742. doi:10.1126/science.1085169. PMID 12805546.

External links

• International Partnership for the Hydrogen Economy
• European Hydrogen Association
• Canada
• U.S.-Department of Energy
• European Projects 2002-2006 FP6
• European Projects 2007-2013 FP7
• 20 Hydrogen myths - Published by the Rocky Mountain Institute, a major hydrogen economy proponent.
• Does a Hydrogen Economy Make Sense?
• Hydrogen and Fuel Cell Wiki