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Hybrid photovoltaic/thermal collectors (PV/T) usually consist of common photovoltaic modules cooled by a suitable fluid, and convert solar radiation simultaneously into both thermal and electric energy. The heat transfer between PV cells and cooling fluid allows lowering the temperature of the PV cells, thus improving their efficiency; it also generates low-grade heat made available for specific applications. As a consequence, PV/T modules have a very interesting overall energy efficiency.
In this paper, the Second Law analysis of a water-cooled PV/T module is discussed; the study aims to underline one main drawback for the optimal exploitation of such a technology: the electricity production from PV cells increases at low temperatures, whereas the usability of the thermal energy is higher at high temperatures.
The results may allow a real optimization of PV/T collectors, and lead to the definition of those operational conditions that maximize the total exergy harvested by the system.
PV panels, mathematical modeling, heat recovery, exergy efficiency
This research has been developed in the framework of the industrial research project on “New Photovoltaic Technologies for Intelligent Systems Integrated in Buildings” (PON 01_01725), financed by the Italian National Program on Research and Competitiveness 2007-2013.
[1] M. Cucumo, D. Cucumo, A. De Rosa, V. Ferraro, D. Kaliakatsos, V. Marinelli, Analisi teorica di un collettore solare cogenerativo PV/T a liquido, Atti Congresso Nazionale ATI, 2009.
[2] N. Aste and F. Groppi, Impianti solari termici – Manuale per ingegneri, architetti, installatori, Editoriale Delfino, Milano, 2007.
[3] W.A. Beckman and A. Duffie, Solar Engineering of thermal processes, John Wiley & Sons, 1980.
[4] H.A. Zondag, D.W. de Vries, W.G.J. van Helden, R.J.C. van Zolingen, A.A van Steenhoven, The thermal and electrical yield of a PV-thermal collector, Solar Energy, vol. 72 (2), pp. 113-128, 2002.
[5] T. Fujisawa and T. Tani, Annual exergy evaluation on photovoltaic-thermal hybrid collector, Solar Energy Materials and Solar Cells, vol. 47, pp. 135-148, 1997.
[6] J.S. Coventry and K. Lovegrove, Development of an approach to compare the ‘value’ of electrical and thermal output from a domestic PV/thermal system, Solar Energy, vol. 75, pp. 63-72, 2003.
[7] A.S. Joshi and A. Tiwari, Energy and exergy efficiencies of a hybrid photovoltaic-thermal (PV/T) air collector, Renewable Energy, Vol. 32, pp. 2223-2241, 2007.
[8] A.D. Sahin and M. Rosen, Thermodynamic analysis of solar photovoltaic cell systems, Solar Energy Materials and Solar Cells, vol. 91, pp. 153-159, 2007.
[9] T.T. Chow, G. Pei, K.F. Fong, Z. Lin, A.L.S. Chan, J. Ji, Energy and exergy analysis of photovoltaic-thermal collector with and without glass cover, Applied Energy, Vol. 86, pp. 310-316, 2009. 141
[10] 10.R. Saidur, G. BoroumandJazi, S. Mekhlif, M. Jameel, Exergy analysis of solar energy applications, Renewable and Sustainable Energy Reviews, Vol. 16, pp. 350-356, 2012.
[11] S. Agrawal and G.N. Tiwari, Energy and exergy analysis of hybrid micro-channel photovoltaic thermal module, Solar Energy, Vol. 85, p. 356-370, 2011.
[12] S. Agrawal and G.N. Tiwari, Overall energy, exergy and carbon credit analysis by different types of hybrid photovoltaic thermal air collectors, Energy Conversion and Management, Vol. 65, pp. 628-636, 2013.
[13] 13.A. Bejan and M.J. Moran, Thermal Design and Optimization, John Wiley & Sons, 1996.
[14] 14. M. Pons, On the reference state for exergy when ambient temperature fluctuates, International Journal of Thermodynamics, vol. 12 (3), pp. 113-121, 2009.
[15] 15.R. Petela, Exergy of heat radiation, ASME Transaction Journal of Heat Transfer, vol. 2, pp. 187-192, 1964.
[16] 16. M. Pons, Exergy analysis of solar collectors, from incident radiation to dissipation, Renewable Energy, vol. 47, pp. 194-202, 2012.
[17] 17. S.M. Jeter, Maximum conversion efficiency for the utilization of direct solar radiation, Solar Energy, vol. 26 (3), pp. 231-236, 1981.