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Adiabatic storage power plants
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Axial-radial compressor, suitable for the low pressure component (LP in fig. 4)
© MAN TURBO AG, Oberhausen
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AA-CAES - research objectives

'Adiabatic storage power plants' (AA-CAES) store not only the compressed air, but also the heat (in a separate heat storage tank) which is released upon compression of the air (fig. 3). For generation of electricity, the heat is returned to the compressed air which flows to the turbine. This renders the use of natural gas unnecessary. Operated with only regenerative electricity, AA-CAES should achieve efficiency of up to 70 %. The development of such plants is supported by the European Union, but is still in its infancy. Almost all components must be newly developed. The researchers are correspondingly cautious with predictions as to when the technology will be ready for implementation. A demonstration power plant could be built in five to ten years. Until then, there are still numerous challenges to overcome:

Heat storage tanks with a storage capacity of up to 1,200 MWth at temperatures of over 600 °C are required. Two lines of development are being investigated:

  • Solid stores made of ceramic, natural stones, concrete, or cast iron, could be directly charged and discharged. They have proven themselves in industry, are simple in structure, and have a large heat transfer surface. However, solid stores require a pressure-resistant shell.
  • Another technology, also proven many times over in industry, uses commercially available fluids. Charging and discharging occur via heat exchangers, so corresponding temperature losses and pressure losses are incurred. But on the other hand, low-cost containers can be used.

Compressors for charging the store should cope with temperatures of up to 600 °C, and generate pressures of up to 160 bar. Other requirements are: high efficiency, a variable flow rate, and rapid availability with a start-up time of a few minutes. Design studies for appropriate radial compressors are encouraging.
Air turbines must be newly developed, to achieve capacities of up to 300 MW by expansion of the compressed hot air to atmospheric pressure. Here, the challenges include: high power density, high entry temperatures, large volume flows, and changes in volume flow. Simultaneously, high efficiency should be achieved across the entire load range, with low specific costs.

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Project coordination
RWTH Aachen, IAEW