Energy Storage Systems

A New Era in Energy Storage

Power generation is going through a major change.

The market share of unpredictable renewable generation has dramatically increased and will continue to make up an ever-increasing proportion of total global capacity. Coal and nuclear plants will be retired and are unlikely to be replaced due to high CAPEX and environmental issues.

Gas turbines' technical characteristics make them the industry choice for flexible generation - they enjoy low CAPEX, but suffer from higher fuel costs.

With a greater proportion of power generation coming from renewable sources there is a strong incentive to develop energy storage technologies.

In addition to standalone electricity storage, Isentropic Ltd is developing energy storage systems which can be integrated into both new and existing gas power plants.


Pumped heat electricity storage (PHES) is our original energy storage system. It will be the lowest-cost site-independent method of storing electricity.

How Isentropic PHES Works

The cycle uses a proprietary reciprocating heat pump/engine developed in-house by Isentropic Ltd, powered by electricity from the grid, to charge Isentropic Thermal Stores.

The heat pump compresses argon gas up to 12 bar and 500°C. The gas then passes through crushed rock in a pressure vessel, the “hot store”. This crushed rock is an inexpensive, abundant and safe medium of energy storage.

The argon gas, now at near-ambient temperature, exits the hot store and enters a second heat pump cylinder. In that cylinder, it is expanded down to around 1 bar, which cools it to -160°C. This cold gas enters a second thermal store, the “cold store”, cooling its contents.

The argon gas is now at ambient pressure and ambient temperature, and the cycle recommences.

The cycle stores electrical energy as a temperature difference. When the electricity is needed again, the temperature difference is used to drive the heat pump as a heat engine, driving a generator and producing electricity.

Isentropic Ltd has designed a number of key features in the heat pump/engine and thermal stores that will enable a round-trip efficiency of 70-75% (ac to ac).

The use of natural materials allows for a projected ex-factory cost of $140/kWh.

The components are engineered to give each installation a life of 25 years with no limitation on number of cycles or depth of discharge.

PHES combines the three essential features required of an electricity storage technology: high efficiency, low capital cost and long life.


GTI-Boost can increase the power output of a combined-cycle gas turbine (CCGT) plant in a matter of seconds by up to 20%.
With a cost of $250/kW for one hour of boost, GTI-Boost is ideal for generating income from grid services markets.


Isentropic Gas Turbine Integrated - Compressed Air Energy Storage

GTI-CAES (gas turbine integrated compressed air energy storage) integrates an Isentropic Thermal Store and an underground cavern into a combined cycle gas turbine (CCGT) power plant to store the energy created by the compression stage of the gas turbine. The requirements both for flexible primary electricity generation and for electricity storage are combined in this technology, since the gas turbine can be used as a conventional power source and for storage charge/discharge.

With a capital cost of only $618/kW for 6 hours of storage ($375/kW power machinery and $40/kWh stored energy) and a round-trip efficiency in excess of 90% this has both lower capital cost and lower marginal generating cost than a conventional CCGT. These figures are confirmed in a detailed analysis by engineering consultants Parsons Brinckerhoff. For large scale energy storage it has the potential to revolutionise power generation.


The ultra low cost and high efficiency make this a commercially and technically compelling proposition in markets around the world.

The Company is therefore looking to work with power equipment manufacturers and EPCs to commercialise this offering. Contact us to discuss this further.