Experimental Determination of Power Losses and Heat Generation in Solar Cells for Photovoltaic-Thermal Applications
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JMEPEG https://doi.org/10.1007/s11665-018-3604-3
Experimental Determination of Power Losses and Heat Generation in Solar Cells for Photovoltaic-Thermal Applications Bruno Lorenzi, Maurizio Acciarri, and Dario Narducci (Submitted April 17, 2018; in revised form July 16, 2018) Solar cell thermal recovery has recently attracted more and more attention as a viable solution to increase photovoltaic efficiency. However, the convenience of the implementation of such a strategy is bound to the precise evaluation of the recoverable thermal power and to a proper definition of the losses occurring within the solar device. In this work, we establish a framework in which all solar cell losses are defined and described. The aim is to determine the components of the thermal fraction. We therefore describe an experimental method to precisely compute these components from the measurement of the external quantum efficiency, the current–voltage characteristics, and the reflectivity of the solar cell. Applying this method to three different types of devices (bulk, thin film, and multi-junction), we could exploit the relationships among losses for the main three generations of PV cells available nowadays. In addition, since the model is explicitly wavelength dependent, we could show how thermal losses in all cells occur over the whole solar spectrum, and not only in the infrared region. This demonstrates that profitable thermal harvesting technologies should enable heat recovery over the whole solar spectral range. Keywords
heat recovery, photovoltaic, thermal losses
1. Introduction Photovoltaic (PV) technologies play a dominant role in electric power generation using renewable resources, with PV market expansion and PV conversion efficiency improvements sustaining each other (Ref 1). Enhancements of the solar conversion efficiency are therefore highly desirable to promote further diffusion of solar converters (Ref 2). A possible way to improve solar energy conversion comes from technologies combining PV devices with systems able to recover the heat unavoidably produced within solar cells. Co-generation of warm water or the use of thermoelectric generators (TEGs) provides typical examples (Ref 3-8). In all cases, the profitability of hybrid solar harvesters is limited by the requirement of keeping PV cells at the lowest possible temperature, as their efficiency decreases with temperature at a rate depending on the specific PV material. This is a very well-known hurdle in the making of effective hybrid solar cells, as reported in previous papers by the present authors (Ref 9) and by other This article is an invited paper selected from presentations at ‘‘GiTE 2018’’ (Thermoelectricity Days), held February 21-22, 2018, in Santa Margherita Ligure, Italy, and has been expanded from the original presentation. Bruno Lorenzi, Department of Materials Science, University of Milano Bicocca, Via R. Cozzi 55, 20125 Milan, Italy; and Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; Maurizio Acciarri and Dario N
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