Exergy analysis of a solar photovoltaic module

Serrano-Casares, Francisco Víctor; Zaragoza, E.

Exergy analysis of a solar photovoltaic module

Serrano-Casares, Francisco Víctor,Zaragoza, E.

Published: 2016-07-07
Repository: riuma.uma.es
Language: en

Abstract

PV energy is the direct conversion of solar radiation into electricity. In this paper, an analysis of the influence of parameters such as global irradiance or temperature in the performance of a PV installation has been carried out. A PV module was installed in a building at the University of Málaga, and these parameters were experimentally determined for different days and different conditions of irradiance and temperature. Moreover, IV curves were obtained under these conditions to know the open-circuit voltage and the short-circuit current of the module. With this information, and using the first law of thermodynamics, an energy analysis was performed to determine the energy efficiency of the installation. Similarly, using the second law of thermodynamics, an exergy analysis is used to obtain the exergy efficiency. The results show that the energy efficiency varies between 10% and 12% and the exergy efficiency between 14% and 17%. It was concluded that the exergy analysis is more suitable for studying the performance, and that only electric exergy must be considered as useful exergy. This exergy efficiency can be improved if heat is removed from the PV module surface, and an optimal temperature is reached.

Full text

Exergy Analysis of a Solar Photovoltaic Module F. Serrano-Casares and E. Zaragoza Escuela Tecnica Superior de Ingenieria Industrial. Universidad de Malaga Campus de Teatinos E29071-Málaga (Spain) e-mail: fserr[email protected] ENERGY EFFICIENCY: Figure 1. Exergy balance of the module on a sunny day. E G R ENERGY GROUP 𝜂𝜂𝑒𝑒𝑒𝑒 =𝑉𝑉0𝐶𝐶 ·𝐼𝐼𝑆𝑆𝐶𝐶 ·𝐹𝐹𝐹𝐹 𝐴𝐴·𝐺𝐺 EXERGY EFFICIENCY: Exergy analysis includes aconsideration of energy quality or capability.This analysis quantifies both the usable energy (availability)and unusable energy (irreversibility), which allows amore effective and efficient evaluation of the use of energy potential to know the efficiency in energy utilization. Figure 2. Exergy and energy efficiency of the module on a sunny day. 𝜂𝜂𝑒𝑒𝑒𝑒 = 𝑉𝑉0𝐶𝐶 ·𝐼𝐼𝑆𝑆𝐶𝐶 ·𝐹𝐹𝐹𝐹 +𝑄𝑄1−𝑇𝑇 𝑎𝑎 𝑇𝑇 𝑚𝑚 𝐴𝐴𝐺𝐺 1−4 3 𝑇𝑇 𝑎𝑎 𝑇𝑇 𝑠𝑠 +1 3 𝑇𝑇 𝑎𝑎 𝑇𝑇 𝑠𝑠 4 In Figure 1, one can see the exergy input and the exergy output, divided in electric exergy and thermal exergy.It can also be seen that the exergy loss is very high, constituting around 85%of the exergy input, due to irreversibilities in the process. In Figure 3, it can be seen that the efficiency is proportional to the module temperature.Common sense tells us that increasing the module temperature should not be beneficial for exergy efficiency, as thermal losses increase with temperature,and thus irreversibilities.Therefore, we came to the conclusion that thermal exergy should not be considered as an exergy output, but rather an exergy loss. CORRECTED EXERGY EFFICIENCY: 𝜂𝜂𝑒𝑒𝑒𝑒 =𝑉𝑉0𝐶𝐶 ·𝐼𝐼𝑆𝑆𝐶𝐶 ·𝐹𝐹𝐹𝐹 𝐴𝐴𝐺𝐺 1−4 3 𝑇𝑇 𝑎𝑎 𝑇𝑇 𝑠𝑠 +1 3 𝑇𝑇 𝑎𝑎 𝑇𝑇 𝑠𝑠 4 Figure 3. Exergy efficiency, module temperature and ambient temperature of the module on a sunny day. Figure 4. Corrected exergy efficiency and module temperature on a cloudy day. ACKNOWLEDGEMENT The authors wish to thank to Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech the support for presenting this work.