Photovoltaic Array Conversion Efficiency and Fill Factor Performances under Varying Intensity of Solar Irradiance

摘要

The overall performance of a photovoltaic array varies with varying irradiance and temperature. However, since most locations on earth are characterized by their different microclimatic seasonal conditions typified by respective average seasonal temperatures, it is reasonable to consider the performance of a photovoltaic array under varying irradiance while the temperature is kept at the seasonal average value. With the change in the time of day during each season the power received from the sun by the photovoltaic array changes. Two important performance parameters of the array that are affected by these changes are conversion efficiency and fill factor. The aim of this paper is to present the experimental results of the effects of changing irradiance on these array performance parameters. Although there are well documented efforts on the effects of irradiance on photovoltaic cell and module efficiencies, such efforts have not been extended to a complete array size. Although photovoltaic cell or module efficiency values may be analytically scaled to obtain corresponding array size values, this approach is not accurate due to obvious mismatch considerations. Furthermore, there are limited studies on the effect of irradiance on the fill factor of photovoltaic arrays. In this paper, effort has been made to document clear effects of irradiance on conversion efficiency and fill factor of a photovoltaic array installed at the Faculty of Engineering and Engineering Technology of Abubakar Tafawa Balewa University, Bauchi, Nigeria. Measurements were carried out to obtain exact dependence of conversion efficiency and fill factor on irradiance for the PV array. The measurements covered the 3 major microclimatic weather conditions of harmattan, cloudy and clear sunny seasons. Regression analysis is then performed on the data to obtain empirical relationships between fill factor and irradiance and between irradiance and conversion efficiency for all the seasons. The results show that both the conversion efficiency and fill factor of the array have a polynomial relationship with irradiance. The array attains its highest energy conversion efficiency of 13.12% during harmattan, while having a least efficiency of 12.17% during the clear sunny season. Similarly, the PV array attains its highest fill factor of 0.725 during harmattan while having its least fill factor of 0.0.697 during the clear sunny season. Furthermore, the exact empirical polynomial equations relating conversion efficiencies and fill factors of the array have been determined thus making it possible to predict the values of these parameters for any irradiance value during any of the prevailing weather conditions.