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Power storage can improve the efficiency and reliability of the electric utility system by reducing the requirements for spinning reserves to meet peak power demands, making better use of efficient base load generation, and allowing greater use of intermittent renewable energy technologies. Energy storage technologies include utility battery storage, flywheel storage, superconducting magnetic energy storage, compressed air energy storage, pumped hydropower, and super capacitors. Additionally, hydrogen may be used as an energy storage medium.
Since hydrogen is one of the lightest elements and has very small molecules it can escape from tanks and pipes more easily than conventional fuels. However, if it is to be used as a fuel for transport or power generation then there must be ways of storing it cost-effectively. There is also a need to get it from the place where it is generated to the place where it is used.
Storing hydrogen can be done in three main ways: in compressed form, liquid form and by chemical bonding.
Hydrogen Production
Many people think that hydrogen will be both a primary fuel and "energy carrier" (as electricity is today) of the future, and that it will supply the energy we need for heat, electric power, and transportation. We are exploring a number of photo biological and electrochemical ways to produce hydrogen, which is bonded to other elements in nature. One technique we use, photolysis, involves using light to "split" water molecules into hydrogen and oxygen. There is also a significant environmental advantage in using electricity from renewable energy resources (for example, solar and wind energy) to split off the hydrogen from water.
Compressed hydrogen
Compressing hydrogen is similar to compressing natural gas, though as hydrogen is less dense the compressors need better seals. Hydrogen is normally compressed to between 200 and 250 bar for storage in cylindrical tanks of up to 50 liters. These tanks may be made from aluminum or carbon/graphite compounds and can be used for either small industrial projects or transportation. If the compressed hydrogen is to be used on a larger scale then pressures of 500-600 bar may be employed, though some of the largest compressed hydrogen tanks in the world (about 15,000 cu meters) use pressures of only 12-16 bar.
Liquid hydrogen
In order to reduce the volume required to store a useful amount of hydrogen - particularly for vehicles - liquefaction may be employed. Since hydrogen has does not liquefy until it reaches -253°C (20 degrees above absolute zero), the process is both long and energy intensive. Up to 40% of the energy content in the hydrogen can be lost. However, with a renewable power source providing the energy to compress and liquefy gaseous hydrogen such as the Krouse Turbine, this would be a “free” process. The advantage of liquid hydrogen is its high energy: mass ratio, three times that of gasoline. It is the most energy dense fuel in use (excluding nuclear reactions), which is why it is employed in all space programs. However, it is difficult to store and the insulated tank required may be large and bulky.
Bonded hydrogen
Metal and liquid hydrides and adsorbed carbon compounds are the principal methods of bonding hydrogen chemically. They are the safest methods as no hydrogen will be released in the event of an accident, but they are also bulky and heavy.
Metal hydrides such as FeTi compounds are used to store hydrogen by bonding it to the surface of the material. To ensure that large volumes of hydrogen can be stored it is essential to use small granules of the base material to make a large surface area available. The material is 'charged' by injecting hydrogen at high pressure into a container filled with the small particles. The hydrogen bonds with the material and releases heat in the process, and this heat must be put back in to release the hydrogen from its bond.
Carbon adsorption techniques rely on the affinity of carbon and hydrogen atoms. Hydrogen is pumped into a container with a substrate of fine carbon particles where it is held by molecular forces. This method is about as efficient as metal hydride technology but is much improved at low temperatures, where the distinction between liquid hydrogen and chemical bonding needs to be considered.
(some parts reprinted from www.nrel.gov)
Hydrogen Storage
There are many environmental benefits to using hydrogen as a fuel. In addition to the possibility of producing it using hydropower or micro-hydropower, which are environmentally benign, hydrogen burns without pollution--it produces only water vapor. This makes it a very attractive transportation fuel. Unfortunately, a convenient automotive hydrogen storage system does not exist today. The current technologies include compressed gases (like propane and natural gas are transported), which occupy large volumes, and metal hydrides, which are very heavy and therefore result in a reduced driving range. Carbon nanotubes are essentially tiny, lightweight cylinders with diameters the size of several hydrogen molecules, and they may provide a solution to the storage problem. Researchers at NREL have shown that hydrogen may be drawn up into these carbon tubes just as water is drawn up into a drinking straw. Researchers around the United States are working to fabricate bundles of aligned nanotubes. Such a configuration would essentially be a light-weight hydrogen sponge ideal for a vehicular hydrogen storage system. This system could easily integrate with Hydro Green Energy's Krouse Turbine to provide a stand-alone hydrogen production and storage unit that allow the generation and storage facility to be placed close to point sources of need.
Fuel Cells
Hydrogen and oxygen are also important components of advanced fuel cell technologies, which convert the chemical energy of a fuel directly into electrical energy without generating airborne pollutants. In a typical fuel cell, hydrogen and oxygen react electrochemically at separate electrodes, producing electricity, heat, and water. Fuel cells are an efficient link between alternative fuels (such as hydrogen) and electricity production.
Transport and Storage
The use of hydrogen as a fuel and energy carrier will require an infrastructure for safe and cost-effective hydrogen transport and storage.
Existing Transport and Storage Methods
Hydrogen is currently stored in tanks as a compressed gas or cryogenic liquid. The tanks can be transported by truck or the compressed gas can be sent across distances of less than 50 miles by pipeline. Hydro Green Energy's Krouse Turbine could provide a stand-alone hydrogen production and storage unit that allow the generation and storage facility to be placed close to point sources of need.
Compressed hydrogen
Compressing hydrogen is similar to compressing natural gas, though as hydrogen is less dense the compressors need better seals. Hydrogen is normally compressed to between 200 and 250 bar for storage in cylindrical tanks of up to 50 liters. These tanks may be made from aluminum or carbon/graphite compounds and can be used for either small industrial projects or transportation. If the compressed hydrogen is to be used on a larger scale then pressures of 500-600 bar may be employed, though some of the largest compressed hydrogen tanks in the world (about 15,000 cu meters) use pressures of only 12-16 bar.
Liquid hydrogen
In order to reduce the volume required to store a useful amount of hydrogen - particularly for vehicles - liquefaction may be employed. Since hydrogen has does not liquefy until it reaches -253°C (20 degrees above absolute zero), the process is both long and energy intensive. Up to 40% of the energy content in the hydrogen can be lost. However, with a renewable power source providing the energy to compress and liquefy gaseous hydrogen such as the Krouse Turbine, this would be a “free” process. The advantage of liquid hydrogen is its high energy: mass ratio, three times that of gasoline. It is the most energy dense fuel in use (excluding nuclear reactions), which is why it is employed in all space programs. However, it is difficult to store and the insulated tank required may be large and bulky.
Bonded hydrogen
Metal and liquid hydrides and adsorbed carbon compounds are the principal methods of bonding hydrogen chemically. They are the safest methods as no hydrogen will be released in the event of an accident, but they are also bulky and heavy.
Metal hydrides such as FeTi compounds are used to store hydrogen by bonding it to the surface of the material. To ensure that large volumes of hydrogen can be stored it is essential to use small granules of the base material to make a large surface area available. The material is 'charged' by injecting hydrogen at high pressure into a container filled with the small particles. The hydrogen bonds with the material and releases heat in the process, and this heat must be put back in to release the hydrogen from its bond.
Carbon adsorption techniques rely on the affinity of carbon and hydrogen atoms. Hydrogen is pumped into a container with a substrate of fine carbon particles where it is held by molecular forces. This method is about as efficient as metal hydride technology but is much improved at low temperatures, where the distinction between liquid hydrogen and chemical bonding needs to be considered.
(some parts reprinted from www.nrel.gov)
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