Experimental evaluation of a stationary parabolic trough solar collector: Influence of the concentrator and heat transfer fluid

Abstract

In this article, a parabolic trough solar collector (PTC) was built and evaluated in different configurations. The prototype was built to minimize the cost and complexity of construction and operation since these are the main difficulties related to the dissemination of this type of system. PTC was designed to operate stationary and the thermosyphon regime was used to eliminate pumping dependence. The evacuated glass receiver tube was connected directly to the thermal storage system, to avoid using additional connections. PTC was evaluated under different configurations, incorporating a concentrator or not, and using different heat transfer fluids (HTF): water and thermal oil. Parameters such as optical efficiency, thermal performance, and general coefficient of thermal loss were calculated. Despite reducing the thermal efficiency of the system, the use of the concentrator contributed to an increase of approximately 97% in the total useful energy gain. With the use of the concentrator, the maximum instantaneous efficiencies were obtained when the angle of solar incidence was close to zero and gradually reduces as the angle moves away from this value. The maximum overall heat loss coefficient of the system was 1.50 W K−1 demonstrating that the isolation of the PTC was adequate. The proposed system proved to be economically viable, with an average level heating cost of 0.035 US$ kWh−1. The proposed PTC is a high potential alternative for several medium temperature agro-industrial applications, where high efficiency is not necessary and ease of operation is important.