Storelectric: aiming to breathe new life into CAES 19 February 2016

The idea of using compressed air for energy storage is not new, nor is the concept of using naturally occurring salt caverns rather than manufactured vessels. But to date commercialisation has proved challenging. UK-based start-up Storelectric is hoping to bring some new thinking to the technology with the aim of increasing efficiencies and reducing costs.

It has developed and owns the IPR for what it describes as an "innovative form" of compressed air energy storage (CAES) that has "the potential for rapid international rollout" and "can address the vast market disruption and system risk caused by the mass build-up of renewable energy."



The only two commercial scale compressed air storage facilities currently in operation, Huntorf, Germany, and McIntosh, USA (entering service in 1978 and 1991, respectively) employ the compressed air in gas fired power plants for regeneration, limiting efficiency and creating emissions, while the proposed Storelectric scheme concept does not require fossil fuel, employing a compressor and expander in conjunction with a thermal management system.



Similar fossil-fuel-free compressed air energy storage schemes have been proposed before and are under various stages of development around the world, but Storelectric believes its approach has particular advantages. "We have both innovated and simplified the process, and sought out existing technologies with which to embody it," the company says. It says its partners have analysed its proposed processes and identified "specific proven equipment and designs that will deliver it", corroborating an efficiency of 62.3% for a 40 MW pilot plant, "expected to be 68-70% efficient when scaled up to a full 500 MW, 21 GWh" - with the possibility of getting to 75- 85% with existing technologies (compared with an estimated threshold for viability of 60%).



The cost of the first full scale facility is estimated to be about £400 million, dropping subsequently to less than £300 million.



Storelectric believes it can achieve a levelised cost of electricity of £100/MWh, "cheaper than gas-fired peaking plants" and levelised cost of storage of £68/MWh, "cheaper than pumped hydro."



Already partnering with PwC, Storelectric says it is currently in advanced detailed discussions with the likes of Siemens, Balfour Beatty, GE etc, with aim of finalising the design and developing what it describes as "a standardised roll out facility of 500 MW."



The current focus of activity is in the United Kingdom, which, in common with most of Europe, is facing a severe energy challenge, says Storelectric, pointing out that over the last three years, the electricity generating capacity margin has fallen from 17% to 4% and is still declining. This has been caused mainly by an ongoing programme of closure of aging baseload power stations, including coal and nuclear.



In addition, political emphasis has been placed on building renewable sources of electricity, predominantly wind and solar power. Wind and solar are, by definition, not base load but "peaky"; the power is only available when natural weather conditions allow, not always when the power is needed. This type of power generation is not capable of fast response when there is an urgent need for power to support a surge in demand. Wind power in particular often produces electricity at night when it is not required and cannot then respond to peak surges in demand. So the investment in renewables has disrupted the traditional power market, marginalising conventional power stations, but is unable to respond to peak demand, Storelectric notes.



The quickest and most effective solution to this problem is to harness renewable energy when it is available and store it for when it is needed. Energy can be "harvested" when it is available at low demand times and therefore cheaper; then released when the demand and price is higher. Storage can smooth the current demand-supply imbalance of the grid system and is available very quickly to meet a surge in demand.



The Storelectric proposal for the UK is storage of compressed air in underground salt caverns. Renewable energy is utilised at low cost low demand times to operate compressors to fill the underground caverns with compressed air. Large numbers of salt caverns are available, both in the UK (for example in Cheshire) and internationally, says Storelectic, and more can be made cheaply. Salt caverns are naturally hermetic and "self-healing" thus providing an effective natural seal, the company says. The concept has been known about for many years, but "until now it has not been possible to convert the compressed air cost effectively", says Storelectric. "This has now changed, also political emphasis has changed. The need for storage has now become critical", with "electricity storage poised to be the biggest growth industry of the 21st century."



The University of Chester in the UK is building the first demonstration and test facility with Storelectric. Capable of generating 200 kW for 10 hours, it is being built at the university's Thornton Science Park and will also have a secondary role of proving the concept of 100% renewable energy back up at a building scale, eg for hospitals. Currently, "such back up comes from heavily polluting diesel generators", notes Storelectric.



In parallel with this first step, work is continuing to develop the first commercial grid-scale project, at a location in Cheshire, where there are five caverns ready for operation. This facility will be capable of 20 MW for 50 hours and is planned to be operational within two years.



In parallel with both of these activities, Storelectric says work is continuing to develop the first full-scale commercial facility, capable of 500 MW, again in Cheshire, and planned to be operational within four years.



Storelectric introduced its technology to a group of companies/organisations to develop the system design and costing further, to construct a proven prototype and prepare for the installation of the 500 MW facility:



• Siemens - who are contributing to the pump and generation design, using predominantly off-the-shelf equipment.

• PwC - financial and strategic adviser to Storelectric, with an equity interest, whose advice covers the negotiation of the joint venture between the companies, developing the commercial and revenue contracting strategy of the JV, full financing of the 500 MW plant, roll-out strategy and exit.

• GE (formerly Alstom) - thermal management technology, involving releasing the heat of compression to the cold of expansion, leading to high closed- loop round-trip efficiencies.

• Civil engineering - Balfour Beatty is currently looking at project management, as well as detailed costings for the civil engineering aspects of the 500 MW plant.

• Six universities - Manchester, Imperial College, Chester, Lancaster, UCLan and UCD.



Storelectric points out that its pilot plant plus first full-scale plant has been recognised as a "project of common interest" by ENTSO-E.



Among its competitors, Storelectric identifies Dresser Rand ("traditional" concept with compressed air used in gas combustion), isothermal technology developers (Lightsail and General Compression (recently merged with

SustainX), and adiabatic system developers (ADELE consortium and Chinese Academy of Sciences).



A problem for isothermal systems, says Storelectic, is the need to "re-invent" compressor and expander technology, including reciprocating compressors capable of handling sufficiently high speeds and capacities.



Use of cylinders for compressed air storage is much more expensive than the salt caverns, with Storelectric estimating that a 1 million m3 salt cavern costs less than a 1000 m3 cylinder.



A problem for adabiatic systems is large scale thermal storage, with the ADELE ceramic thermal store (equivalent to "two night storage heaters, each as big as a tower block") proving problematic, entailing high costs and large parasitic loads.

(Originally published in MPS January 2016)