> As I understand gas turbines are around 64% efficient with various tricks. These super-high efficiency gas turbines are not 'pure' gas turbines, but so-calle

> As I understand gas turbines are around 64% efficient with various tricks. These super-high efficiency gas turbines are not 'pure' gas turbines, but so-called combined cycle plants. Basically you first have a 'normal' gas turbine driving a generator (which, by itself, maybe gives you ~45% efficiency), but then you take the host exhaust of that gas turbine and use that to drive a secondary steam cycle driving another generator. I'm not sure such a thing is doable in a closed Brayton cycle, at least I haven't read anything about anything like that. An interesting thing with closed cycle Brayton is that instead of air you can use another fluid as the working fluid. Supercritical CO2, for instance, has some nice properties leading to extremely compact machinery. Of course there's an uphill battle in commercializing this technology; if you use air (or nitrogen) you can just adapt one of the many existing gas turbine cores with $zillions of R&D and decades of experience behind them.