Electricity can be stored directly for a short time in capacitors, somewhat longer electrochemically in, and much longer chemically (e.g. hydrogen), mechanically (e.g. pumped hydropower) or as heat. The first pumped hydroelectricity was constructed at the end of the 19th century around in Italy, Austria, and Switzerland. The technique rapidly expanded during the 1960s to 1980s,.
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is a storage form whereby hydrogen gas is kept under pressures to increase the storage density. Compressed hydrogen in hydrogen tanks at 350 bar (5,000 psi) and 700 bar (10,000 psi) are used for hydrogen tank systems in vehicles, based on type IV carbon-composite technology. Car manufacturers including Honda and Nissan have been developing this solution.
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