Thermal energy storage can be integrated to new or existing CCGTs in a variety of ways, including fast start up and augmentation of steam flow. The thermal energy storage is charged (heated) by surplus electrical energy and then discharged in the form of steam when required.
The most efficient use of this stored energy (extracted in the form of steam) is to maintain temperature in the STG during a short term shutdown or introduce temperature into the HRSG and STG in advance of a start-up so the entire generating capacity of the CCGT (both GTG and STG) can achieve rated output at optimum operating efficiency as close as possible to the time of required dispatch.
The use of stored energy to undertake this function is highly efficient because it increases the flexibility and responsiveness of the CCGT unit using energy that would otherwise have been wasted. Round trip efficiency is high because the relatively small amount of energy used to heat the system results in substantially more generation at a marginal heat rate of zero – i.e. more generation from the same amount of fuel.