Experimental evaluation of a solar window incorporating rotationally asymmetrical compound parabolic concentrators (RACPC)

Building integrated photovoltaic (BIPV) systems have been proposed to make solar photovoltaic systems more attractive. These systems are not only capable of generating electricity, but can also contribute to minimise energy consumption in buildings by providing natural illumination, space and water heating, ventilation and shading. Despite these advantages, one of the issues that still prevents the widespread adoption of BIPV systems is their high capital cost. This paper discusses a novel type of non-imaging optical concentrator that can be used to reduce the capital cost of a BIPV system. This new concentrator, known as rotationally asymmetrical compound parabolic concentrator (RACPC), has a flat entrance aperture that facilitates integration within a double-glazing window and reduces fabrication costs. The RACPC, which has a geometrical concentration of 3.66x, also offers other advantages over conventional solar concentrators: suitability for fenestration, ease of integration with square PV cells, and passive tracking. Several experiments were carried out on a double-glazing solar window incorporating an array of 4x3 concentrator-PV cells. The experiments were carried out indoors under standard test conditions. The results show that the RACPC-PV window effectively increases the short-circuit current by a factor of over 3 at normal incidence when compared with a non-concentrated solar window. The solar window also shows an increase in maximum power generation by a factor of nearly 3.