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Highview’s 300kW/2.5MWh CES plant at SSE’s Slough Heat and Power plant, UK. The project has been supported by the UK Govt’s Dept. of Energy and Climate Change (DECC).

         

             

                                           

                 

                                         

Cryogenic Energy Storage (CES) – briefing note

CES involves four core processes:

1. Charge: The system operates by using electrical energy (excess or off-peak) to drive an air liquefier. Similar equipment is widely deployed for the production of bulk liquid LNG, nitrogen, oxygen or argon. 2. Storage: The liquid air is stored in an insulated tank at low pressure, which functions as the energy store. Again, such equipment is widely deployed as bulk liquid LNG, nitrogen, oxygen or argon storage, and millions of tonnes of liquefied gases are commercially stored and transported around the world. 3. Regasification / Power Recovery: When power is required, liquid air is drawn from the tank and pumped to high pressure. Ambient (or above ambient waste*) heat is applied to the liquid air via heat exchangers resulting in a phase change from liquid air to a high pressure gas which is then used to drive a turbine and generator. Novelty: Cold Recycling: During the power recovery, very cold gas is exhausted, which is then recycled back into the liquefaction process (stage 1) reducing the energy demands for producing liquid air and thereby increasing the overall round-trip efficiency.  

Cryogenic Energy Storage (CES), also referred to as Liquid Air Energy Storage (LAES). The word “cryogenic” refers to a gas in a liquid state at very low temperatures. The working fluid is Liquefied Air or Liquid Nitrogen (78% of air). Uniquely the systems can also harness low grade waste heat from co-located processes, converting it to electricity. Although Highview’s process is novel at a system level (patents pending), as a whole it draws heavily on established processes from the turbo-machinery, power generation and industrial gas sectors. The components and sub-systems are mature technologies available from major OEMs. Highview is currently at Grid-connected pilot demonstration stage: 300kW/2.5MWh, hosted in the UK (Slough nr. London). A multi-MW commercial demonstrator project is in advanced development.    

* Added value: Harnessing waste heat (optional). The introduction of waste heat (including low grade waste heat i.e. sub 100°C) into the power recovery system (stage 3) increases the amount of power which can be extracted. Waste heat is added through heat exchangers rather than direct into the turbine to simplify its capture. Given working fluid is cryogen (-196°C), it can use low grade/very low grade waste heat. The systems convert waste heat to power at approx. 40-50% efficiency. i.e. 4 x typical Organic Rankine Cycle processes.    

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