Abstract
Design processes and analytical modeling are presented showing creation of a low-cost concentrating photovoltaic thermoelectric (PV/TE) hybrid power system for research and laboratory teaching built using a small upcycled satellite dish. Today, concentrated solar hybrid PV/TE systems are drawing significant research attention and funding investment. However, the literature lacks examples of how this cutting-edge energy technology can be made accessible at low cost for STEAEM education at universities, vocational institutions, and high schools. By applying Energy Engineering Laboratory Module (EELM (TM)) design principles and pedagogy, a process is presented to make this technology easily accessible at low cost.
The concentrating solar hybrid PV/TE system presented here is divided into four subsystems: 1) a concentrator, 2) a PV/TE generator, 3) data acquisition, and 4) a cooling system. The key engineering decisions governing the design for each sub-system are described. In addition, a thermodynamic analysis is presented to predict the on-sun steady-state temperature profile of the PV/TE generator at the focus of the concentrator and to determine how much electrical power it will produce.
The concentrator used is a salvaged miniature satellite dish, which is coated with mirrored tape to reflect sunlight upon a focal point. Scavenged at no cost, the satellite dish is a sectioned paraboloid of rotation offset from the vertex and the axis of symmetry. However, which paraboloid section the dish represents is unknown. A technique is presented to find the focal point and to use this information to correctly position a shadow-casting gnomon to ensure proper on-sun alignment. A method to experimentally confirm the focal location and size the PV is also provided.
A key research question for solar concentrating hybrid PV/TE power systems at this size scale is whether it is better to actively cool the TE cold side via forced convection or simply allow cooling via natural convection. The thermodynamic heat balance analysis presented to address this question finds that while forced convection does better cool the PV module, increasing its efficiency and power output, the parasitic energy expenditure of the cooling fan far exceeds the additional power produced. It is therefore more beneficial to rely on natural convection on the TE cold side to maximize power production of the overall PV/TE module.
Two experimental apparatuses were built consisting of a PV module backed by TE generators and instrumented with thermocouples to determine the internal temperature gradient while multi-meters read steady-state PV and TE power output. A halogen lamp placed at various distances from this array approximates concentrated sunlight, which is measured via pyranometer. These experiments validate conclusions drawn from the theoretical model.