drive the shaft 16 and thereby to obtain electric energy from the generator 12 in this case since the efficiency in the turbine 14 depends upon the difference in temperature in the incoming hydrogen and the exhaust hydrogen it may be more effective to provide a heater not shown in the hydrogen inlet conduit 22 to improve the operation efficiency of the gas turbine 14 u201c volumetric efficiency u201d in an expansion device such as turbine 14 for use with a generator 12 using ultra low pressures requires the system to utilize a high volume of hydrogen throughput ideally use of low pressure can be subatmospheric and a negative pressure environment relative to ambient may be used to generate electrical power from latent or solar heat the better the volumetric efficiency the more work is obtained from a similar volume of gas since hydrogen gas has a low mw 2 016 it is liable to leak past seals blades vanes more or easier than than higher mw gases like steam mw 18 or dichlorodifluoromethane freon u00ae mw 102 thereby reducing the volumetric efficiency it has been found that a marked increase in the volumetric efficiency of hydrogen in an expansion device can be achieved by operating at very low or subatmospheric pressures hydrogen volume at very low pressure is so high that the percentage of hydrogen that leaks past internal seals or leaks out of the closed system 10 without doing any work is reduced thereby substantially increasing volumetric efficiency and increasing overall expansion efficiency it has also been disclosed that deuterium can replace hydrogen as a diffused gas in metal hydrides while the increase in volumetric efficiency provides a benefit when using molecular hydrogen added or enhanced efficiencies may result from the use of deuterium.