A detailed working fluid investigation for solar parabolic trough collectors

Solar energy is a promising energy source for covering a great variety of applications from low up to high temperature levels. In this study, the most mature concentrating technology, a commercial parabolic trough collector (Eurotrough ET-150), is investigated energetically and exergetically for a great temperature range from 300 K to 1300 K. Pressurized water, Therminol VP-1, nitrate molten salt, sodium liquid, air, carbon dioxide and helium are the examined working fluids; each one to be studied in the proper temperature range. In the first part of this study, the optimum mass flow rate is determined to every working fluid separately. After this point, the exergetic and the energetic performance of the collector operating with all these working fluids is examined. The final results prove that the liquid sodium leads to the global exergetic maximum efficiency (47.48%) for inlet temperature equal to 800 K, while the maximum exergetic performance of helium, carbon dioxide and air to be 42.21%, 42.06% and 40.12% respectively. Moreover, pressurized water is the best working medium for temperature levels up to 550 K, while carbon dioxide and helium are the only solutions for temperatures greater than 1100 K. The thermal analysis is performed with the EES tool.