Overall efficiency improvement of photovoltaic-thermal air collector: numerical and experimental investigation in the de
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ORIGINAL RESEARCH
Overall efficiency improvement of photovoltaic‑thermal air collector: numerical and experimental investigation in the desert climate of Ouargla region Naoui Khenfer1,2 · Boubekeur Dokkar2 · Mohamed Taher Messaoudi1,2 Received: 11 April 2020 / Accepted: 2 July 2020 © Islamic Azad University 2020
Abstract In the Ouargla region, the desert area of Algeria, photovoltaic fields (PV) suffer from hard climate conditions with hightemperature levels. This temperature level causes a significant fall of PV cells efficiency which requires an integrated cooling system. For achieving this purpose, a thermal part based on airflow provided along a straight channel under the PV module (150 W) is added. It extracts the accumulated heat by air natural convection, then, the airflow passes through an upper glass extension (0.56 m) to reinforce the heat collection. The evaluation of the whole system performance is experimentally conducted by performing several variations of operating parameters and air channel depth. This photovoltaic-thermal (PV/T) system has modeled by a set of balanced energy equations that are resolved numerically using Matlab software. The experimental results show that the increase in the channel depth causes a significant reduction of thermal efficiency and a slight effect on the electrical one. The numerical data are compared and validated by the experimental results, where the characteristic curves (efficiencies, polarization, powers, temperatures) show good concordance with experimental data. The root means square of percentage deviation (RMSD) is between 1.75% and 16.25%. For a channel depth of 10 cm, the energy and exergy efficiency reach their mean values of 58.5% and 14.7%, respectively. The glass extension of 1.6 m gives a net improvement of 5% in the overall energy efficiency. Keywords PV/T system · Airflow · Plate absorber · Natural convection · Overall efficiency Nomenclature BIPV/T Building-integrated photovoltaic/thermal CPC Compound parabolic concentrator ER Relative error LCA Life cycle assessments RMSD Root means square deviation PV Photovoltaic PV/T Photovoltaic/thermal
* Naoui Khenfer [email protected] Boubekeur Dokkar [email protected] Mohamed Taher Messaoudi [email protected] 1
Laboratoire de Valorisation et de Promotion des Ressources Sahariennes (VPRS), University of Kasdi Merbah, Ouargla, Algeria
Department of mechanical engineering, faculty of applied sciences, University of Kasdi Merbah, Ouargla, Algeria
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Symbols A Area ACh Cross-section of the channel area bch Breadth of channel ca Specific heat capacity (kJ/kg K) G Solar radiation intensity (W/m2) h Coefficient of heat transfer hp1 Penalty factor hp2 Penalty factor I Circuit current (A) ṁ Air mass flow rate (kg/s) P Power (W) qu Thermal energy (W) qexo Exergy overall (W) T Temperature Ub Overall back loss coefficient from flowing air to ambient through the insulator (Wm−2 K−1) UT Coefficient of conductive heat transfer from the solar cell to air through tedler U
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