At this point it can be stored in tanks, or what Highview call CRYObatteries. Nitrogen comprises 78% of air content, and the gas liquefies at -196☌ (-320☏). This leaves a greater concentration of nitrogen gas, which is then passed through a refrigeration unit and cooled down to a temperature at which the gas becomes liquid. The surplus electricity generated by renewable energy sources will be used to compress air to the point where its carbon dioxide content and water vapour separates out. The new LAES plant to be built by Highview Power takes a big step towards decreasing the UK's carbon emissions. This could mean that waste thermal energy from industrial applications, peak plants (usually gas-powered) and LNG regasification plants could also be channelled to achieve greater efficiencies. The thermodynamic cycle of a LAES plant can also interface with other thermal processes situated in close proximity. It is not, however, a prerequisite, since the system is self-contained and can be located anywhere. This reduces the heat and electricity lost during transmission. Its efficiency is further increased if the plant is located close to its energy source. In order to increase its efficiency, the Highview Power system can harness excess heat that would normally be vented during the cryogenic compression process. Compressing air until it is liquid, as in the proposed LAES or cryogenic battery, can provide energy efficiencies of between 25% and 70%. CAES requires a large underground cavern to store a high volume of compressed air, and is typically only half as efficient (about 40%) in producing electricity as PHS. PHS is relatively (up to 80%) efficient, but requires a lot of water storage space and has a significant environmental footprint. Stored power can be discharged to meet peaks in demand from power plants, and is currently available using the pumped hydro storage system (PHS) or the compressed air energy storage system (CAES). These arise out of changes in the requirements of consumers, power plants or the national grid. Once at high pressure and high temperature, the air is expanded in a gas turbine to produce electricity.Electricity is stored in bulk mainly to accommodate fluctuations in supply and demand. To recover the electricity, the liquid air is passed through a series of exchangers, first with the fluid of the “cold store” for its evaporation and later with the “heat store” to return to a temperature around 400 ✬. Once in a liquid state, the air is stored in tanks until it is time to recover the energy. To extract the heat, another fluid is used, which is also stored in a tank for later use, known as the “cold store”. Then, in the liquefaction process, the air is cooled down to a temperature around -160 ✬. Due to the compression, the air is heated up to 400 ✬ and that heat is carried through an exchanger and stored in molten salt tanks for later use. The process begins with the compression of atmospheric air. To recover the energy, it is followed in a reverse process, heating until the air evaporates and finally decompressing it in a turbine to generate electricity. LAES technology (Liquid Air Energy Storage), stores energy by compressing and cooling air to a liquid state, allowing large amounts of air (and therefore energy) to be stored in a small space.
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