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New heat storage technology on the way

What is said to be the world’s first grid-scale pumped heat energy storage (PHES) system has been commissioned by the technical team at the Sir Joseph Swan Centre for Energy Research at Newcastle University. 

Based in Fareham, Hampshire, the facility includes grid-coupled PHES technology rated at 150 kW and able to store up to 600 kWh of electricity. 

The demonstration facility uses a reversible heat engine, which converts electrical energy to thermal energy and then back again to electrical energy when required.

Taking excess electricity from the grid, the system drives the heat engine to compress argon gas until it reaches 500°C, and stores the heat produced. On the cold side, argon gas is expanded down to a temperature of -160°C. In both cases, the gas is then passed through ‘thermal batteries’ – chambers containing rocks – and gives up its energy to the storage material. The gas then leaves the store at ambient temperature.  What is left behind is a ‘hot rock battery’ and a ‘cryogenic cold battery’, both of which are able to store their energy for up to eight hours.

To release the stored energy, the cycle is reversed. The argon gas flows in the opposite direction and uses the hot and cold energy to turn the heat engine to generate electricity that can be returned to the grid.

During recent testing, the 150 kW reversible heat pump/engine was operated in compression and expansion modes, i.e. as a heat pump and a heat engine, with evidence to support sub-second charge/discharge mode switching. 

The system was originally developed as part of the Energy Technologies Institute (ETI) Distribution Scale Energy Storage Project. With its supporting R&D infrastructure, it puts the UK in a world-leading position in the research and development of low cost and grid-scalable electrical and thermal energy storage, says the ETI.

Dr Andrew Smallbone, Co-Director of the National Facility for Pumped Heat Energy Storage said: ‘Our initial tests have been very promising. We can very quickly change our system control from charge to discharge in a few milliseconds. The analysis of system performance indicated that the current system operates with an efficiency which yields a round trip efficiency of 60–65%. This figure is very exciting… and already sufficiently high to put the technology in the mix for being the lowest cost and most flexible grid-scale energy storage technology.’ 

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