You are terribly overestimating. http://www.tribology-abc.com/abc/thermodynamics.htm http://www.tribology-abc.com/abc/thermodynamics.htm gives just 2kwh for 2

You are terribly overestimating. http://www.tribology-abc.com/abc/thermodynamics.htm http://www.tribology-abc.com/abc/thermodynamics.htm gives just 2kwh for 250L tank at 150atm. Which is at most 10 miles of radius, probably less, and efficiency of about 40%