Testing time for Isentropic thermal store concept

James Macnaghten, CEO, said: "We have built and tested two thermal stores with 12 tons and 26 tons of storage media respectively. Our results demonstrate the concept and confirm theoretical predictions giving a storage efficiency of 98.5%."

The Isentropic thermal store is an enhancement of a packed bed store. In the Isentropic system the store is subdivided into a number of layers. Valves are used to select the layers at which gas enters and leaves the store, restricting gas flow to the part of the store in which store material is actively being heated or cooled. Non-active parts of the store are bypassed.

Since only the thermally active part of the store is exposed to gas flow, pressure drop through the store is significantly reduced. This allows the use of smaller particles than would conventionally be selected. Smaller particles have much better heating and cooling characteristics than larger particles and so the efficiency of the process is increased.

The subdivision of the store into actively controlled layers also allows precise control of the heat exchange process and allows the active part of the store to be much smaller than in a simple, unlayered store. This makes the fraction of the store available for full heating and cooling cycles proportionally bigger, resulting in greater heat storage capacity for a given size of store in conjunction with improved efficiency.

As well as the gas-turbine-integrated storage concept described in last month's issue, Isentropic is developing a stand- alone energy storage system (Pumped Heat Electricity Storage (PHES)), based on a novel, high efficiency reciprocating engine combined with large-scale thermal storage.

Both use Isentropic's layered thermal store technology, with crushed rock employed as the storage medium.

(Originally published in MPS January 2016)