63. Solar Thermal Collectors with Low and High Concentration

This chapter describes the performance analysis of different concentrating technologies through experimental and numerical modeling activities. Two solar thermal systems with different designs and, accordingly, different concentration ratios have been studied. The first solar device is a stationary compound parabolic concentrator (CPC) collector: it is provided with truncated or full CPC reflectors and evacuated tubes. Each evacuated tube is composed of an outer glass envelope and a glass absorber with selective coating in thermal contact, via absorber fin, with a U-shaped channel for the liquid flow. The second system is a parabolic trough concentrator (PTC) with two-axis solar tracking: the primary optics consists of a segment of parabolic cylinder which concentrates the direct normal irradiance (DNI) on a linear receiver. In this system, two types of flat receivers have been tested. One receiver has been designed for thermal energy extraction, and it consists of a canalized roll-bond plate provided with a semi-selective coating. The other receiver has been designed for cogeneration of electricity and heat (CPVT), and it is equipped with triple-junction photovoltaic cells, which are actively cooled by an aluminum roll-bond heat exchanger. The performance of the described collectors has been experimentally characterized at the Solar Energy Conversion Laboratory of the University of Padova (45.4°N, 11.9°E), Italy. The collectors have also been mathematically modeled, and the numerical data have been validated against the experimental measurements.