Analytical approach for performance estimation of BSPVT system with liquid spectrum filters

The terrestrial solar spectrum is not monochromatic; it consists of ultraviolet, visible and infrared radiations. The most commonly used single junction silicon solar cell responds to the visible and near infrared part of the solar spectrum. The ultraviolet and the infrared part of the solar spectrum causes thermal losses in the solar cell, thus reduces its electrical conversion efficiency. In order to reduce these thermal losses, and to improve the conversion efficiency of the solar cells, the concept of spectrum filtration is introduced. Use of liquid spectrum filters for photovoltaic thermal systems (PVT) is reported in some of the recent literatures. In this technique, the selective liquids are used to filter the incoming solar radiations; the desired solar spectrum for photo electricity is only allowed to enter in. The unfiltered part of the spectrum is used separately as heat for the thermal systems. The system gives heat and electricity simultaneously and it is known as Beam Split Photovoltaic Thermal System (BSPVT). The experimental feasibility of these systems has been reported in recent literatures. In the current article, an analytical approach for the performance estimation of a BSPVT system with liquid spectrum filters is reported. C-Si PV module with three different liquids as spectrum filters viz; water, silicone oil and coconut oil are considered. The mathematical analysis is based on the estimation of radiation attenuation by the liquid spectrum filters. The 'Transmissivity Absorptivity product (τα)' of the liquid spectrum filters is determined using Snell's law and Bouger's law. The maximum average thermal and electrical efficiency of the system are estimated as 79% and 14% respectively. The detailed analytical approach is discussed in this article.