thermal cycle is operable with high efficiency for the solar intensity above 600 kcal hr m 2 but otherwise operable with only limited efficiency on the other hand the thermal cycle using the hydrogen pump 38 is operable even for weak solar intensity with desired efficiency but under intense solar energy it suffers from a great heat loss due to its structural complexity therefore such selective operation of the thermal cycles as shown in this embodiment may provide an extensive and stable day time operation with improved efficiency see dotted curve on fig9 it should be understood that although only the automatic selection of the thermal cycles is employed in the above example for dealing with different conditions of temperature or the solar energy intensity manual selection may be alternatively employed when a solar heater is used a timer may be employed for controlled daily operation a third embodiment using zrmn 1 5 co 0 5 al 0 1 as a high temperature alloy mh 1 and with mmni 3 7 co 0 8 used as mh 3 is now is explained as shown in fig1 containers 51 52 that can stand high pressure are filled with about 20 kg of mh 1 ground to about 100 mesh and so are the containers 53 54 with mh 3 ground to about 100 mesh they have respective heat exchangers 55 the containers 51 and 54 are connected with.