Abstract
Based on our field experiment on a solar thermal collector without using optical surfaces, the maximum available temperature of the collector is about 80℃. This paper describes possibility and meaning of a steam Rankine cycle driven under the temperature range of ambient to 80℃. The working fluid is water. According to a simple cycle calculation, thermal efficiency of the present system was estimated 5% at the highest. As far as the present conversion coefficients of the photovoltaic cells (i.e. 5-10%) are concerned, the electricity generated by the solar heat is above 2% of that by the photovoltaic cells. This suggests that the electricity generation by solar heat seems to be very promising, even if the operation temperature of the steam cycle is rather low. On such low temperature cycle, sophisticated pressure control of the system is considered to be one of the major breakthrough subjects.
