Hi there !
Cleantech industry is looking for new technologies to store electricity, storing meaning both consuming electricity during a moment of the day and delivering it back at another time. While a great deal of articles are about how battery would change the world (or not), my personal bet is that thermodynamical technologies are the best suited for mid to large scale distributed energy storage (from 1 to 100 MW). So this is a review of some interesting technologies :
- Compressed Air Electrical Storage (CAES) and Advanced-Adiabatic CAES (AA- CAES)
Storage of electricity through compressing, storing and expanding air is a process well known since the 70s. Here below is main concept (from http://www.arup.com) :
Two existing units of big capacity have been built (and are still in operation), using ground cavern to store the compressed air :
- in 1978, the 290 MW Huntorf plant, in Germany, with discharge capacity of 3 hrs.
- in 1991, the 110 MW McIntosh plant , Alabama, USA with discharge capacity up to 26 hrs. This units works in conjunction with heat recovery fro gas turbine outlet to provide additional energy for the air discharge.
Others prototypes units are said to be in operation, or under development, including for surface CAES, meaning that the air is not stored anymore in cavern, there allowing more places to allow such installation.
– One key drawback of CAES plant is their low efficiency (30 to 40%). Storing separately heat and compressed air in an adiabatic system allows to improve drastically the efficiency of the process up to 65%. You can understand it quiclky with the ADELE concept described :
– Another challenge to overcome is to maintain a relatively stable pressure at turbine outlet during discharge. While emptying the storage, pressure goes down, and therefore, both turbine power (because there is less air flow) & efficiency (because the turbine works out of its nominal point) are reduced.
Among the new developments, you may find the lightsail concept interesting combining a piston power block (reverse generator or motor engine), a close to isothermal compression and featuring a heat capture & storage system. Some additional technical description can be found on one of the founder blog here
Another concept that may be promising is the Hydrostor concept of storing air underwater. Therefore, maintaining a constant pressure while discharging the air storage is possible. With the following video, you may share the concept with your 4years old kids.