Abstract: In one embodiment, an exhaust heat collecting system of collecting exhaust heat in a fluid treatment system. The fluid treatment system includes a fluid path to convey at least an operating fluid or a cooled fluid among first and second heat source fluids, the operating fluid and the cooled fluid. The fluid treatment system further includes a fluid treatment module including an expansion module, a power generator and a condenser for the operating fluid, or including a heat absorbing module and a heat releasing module for the cooled fluid. The exhaust heat collecting system includes a water path to heat water by using the condenser or the heat releasing module, and a heater to heat the water from the water path by using the first or second heat source fluid or the operating fluid to produce the water to be used as hot water or to produce steam.

Abstract: In one embodiment, a solar heat collecting system includes a heat collector configured to heat a heat medium by a sunray, a heating device configured to heat a heat utilizing fluid by heat of the heat medium, and a heat medium flow path configured to circulate the heat medium between the heat collector and the heating device. The system further includes a controller configured to control circulation of the heat medium in the heat collector in accordance with an amount of solar radiation of the sunray, or in accordance with a temperature difference between a first temperature of the heat medium at a first position and a second temperature of the heat medium at a second position located downstream of the first position with respect to the heat medium.