اثر کارایی فتوولتائیک وابسته به دما (PV) بر تولیدات PV در جهان

ABSTRACT Temperature Dependent Photovoltaic (PV) Efficiency and Its Effect on PV Production in the World – A Review

The important role of the operating temperature in relation to the electrical efficiency of a photovoltaic (PV) device, be it a simple module, a PV/thermal collector or a building-integrated photovoltaic (BIPV) array, is well established and documented, as can be seen from the attention it has received by the scientific community. There are many correlations expressing Tc, the PV cell temperature, as a function of weather variables such as ambient temperature, Ta, local wind speed, Vw, and solar radiation flux/irradiance, I(t), with material and system-dependent properties as parameters, e.g., glazing-cover transmittance, , etc. An equally large number of correlations expressing the c, can also be retrieved, although many of them assume the familiar linear form, differing only in the numerical values of the relevant parameters which, as expected, are material and system dependent. With regard to the relevant weather variables, and qualitatively speaking, it was found that the PV cell temperature rise over the ambient is extremely sensitive to wind speed, less to wind direction, and practically insensitive to the atmospheric temperature [1].

On the other hand, it obviously depends strongly on the impinging irradiation, i.e. the solar radiation flux on the cell or module. From the mathematical point of view, the correlations for the PV operating temperature are either explicit in form, thus giving Tc directly, or they are implicit, i.e. they involve variables which themselves depend on Tc. In this last case, an iteration procedure is necessary for the relevant calculation. Most of the correlations usually include a reference state and the corresponding values of the pertinent variables.

The electrical performance is primarily influenced by the type of PV used. A typical PV module converts 6-20% of the incident solar radiation into electricity, depending upon the type of solar cells and climatic conditions. The rest of the incident solar radiation is converted into heat, which significantly increases the temperature of the PV module and reduces the PV efficiency of the module. This heat can be extracted by flowing water/air beneath the PV module using thermal collector, called, photovoltaic thermal (PVT) collectors. In practice, only a-Si and crystalline Si have been found in the literature on PVT. The higher efficiency of crystalline Si will result in a higher electrical efficiency and a higher electrical-to-thermal ratio of the PVT than in the case of a-Si. Tripanagnostopoulos et al. [2] presents experimental measurements on PVT-liquid and PVT-air collectors for both a-Si and c-Si. He finds that at zero reduced temperature, for his PVT liquid collector, the efficiency of his c-Si prototype is 55% and his a-Si prototype 60%, while for his PVT air collector the c-Si prototype is 38% and the a-Si prototype 45%. However, the electrical performance for the c-Si modules is 12% and for the a-Si it is 6%. A higher thermal yield was also found for a-Si by Ji et al. [3]. However, in other experiments a lower thermal efficiency was found for a-Si than for c-Si, Affolter et al. [4, 5] and Platz et al. [6]. Zondag et al. [7] compared a conventional PV module, an unglazed PVT module and a glazed PVT module. The average annual electrical efficiency was found to be 7.2%, 7.6% and 6.6%, respectively. Chow [8] calculated the electrical performance of a thermosyphon PVT collector with the PV at the high end and at the low end of the absorber. For the colder low end, he found a 3% higher electrical efficiency. Naveed et al. [9] examined a PVT air system in which PV was connected to an unglazed transpired collector. It was found that a temperature reduction of 3-9oC resulted in an improved electrical performance, allowing a reduction in PV area from 25 to 23 m2. Krauter and Ochs [10] and Krauter [11, 12] have developed an unglazed integrated solar home system, in which a PV laminate is connected to a triangular water tank. The tank temperature reduction of about 20oC is reported relative to a conventional solar home system, which leads to a 9-12% increase in electrical yield, depending on the stratification.