PHES Thermal Stores are split into layers to achieve
high efficiency of thermal transfer, low pressure drop
and higher energy density than other 'packed bed' stores.
Thermal Stores work by direct heat exchange between high pressure gas and particles of crushed rock or gravel. The design of a 'packed bed' store is normally a compromise between pressure drop and heat transfer. Reducing the particle size improves heat transfer efficiency but smaller particles offer more resistance to gas flow through the store. (The reverse is true for larger particles). The particle size of the storage media must therefore be carefully selected to mediate between these loss mechanisms.
The most important contribution to 'packed bed' storage is the layered store
. Gas flow can be confined to the region where heat exchange is active, termed the 'thermal front', while inactive areas, above and below, are bypassed. This allows the use of small particles for efficient heat exchange whilst maintaining a low pressure drop through the store. Active control of the thermal front allows for much higher energy density by ensuring that the front is kept short.
Simple to Produce
The packed bed is contained within an insulated pressure vessel, such as the ones shown in the image below. The patented thermal store design is unique. Current designs envisage peak pressures of 25 bar and peak temperatures of 550°C. The external pressure vessel can be manufactured by a wide range of suppliers.
Two Thermal Stores installed at our site in Fareham
Following an extensive development programme, we have built two thermal stores with 12 tons and 26 tons of storage media, respectively. A range of successful tests have been conducted which confirm the principles of operation and the efficiency of energy recovery of the system. Energy recovery can exceed 95%.
The video below, generated from test data, shows the movement of a real thermal front through an PHES