Siemens and Oswald Consultancy are working with Storelectric to develop our ideas on CAES into reality. Following a number of iterations, they have developed a system, using only slight modifications of existing products, that achieves 63% efficiency with a 100% renewable CAES system. This is comfortably above the threshold for profitability set by Storelectric at <60% for the higher efficiency peak smoothing operation of our plant. Moreover, it only uses a small part of Storelectric's efficiency improvement ideas.
Because of size and time constraints (it is 7-14 times larger, and stores from season to season rather than for half a day at a time), the mass storage operation of our plant will have to operate with little thermal management and no pressure control. Even so, Siemens and Oswald have developed a 53% efficient system. This burns gas, but only 1/3 of the amount as an equivalent gas-fired power station - and we're all still working on an entirely renewable version of it.