Efficient Operation of Direct Coupled Solar Home PV System: A Case of Solar Home PV System Installed in Dodoma, Tanzania

Abstract

Direct coupled Photovoltaic (PV) system is a common topology among most of the off-grid communities in the world. This topology has less components hence resulting in low investment costs. However, it suffers much losses when battery operating voltage is far from maximum power point voltage of PV modules. This scenario can be attributed by different factors such as; variation in solar radiation, load profile and temperature. Efficient operation of these systems is required in order to reduce losses. Usually in direct coupled system, PV modules are connected in parallel with batteries through a charge controller hence making PV output to depend solely on battery operating points. For losses reduction, a proper voltage range of battery and PV modules has to be selected. The challenge to many technicians is on proper selection of ranges of voltages of battery and PV module. This results in installed PV systems being operating away from maximum power point hence much losses. This paper presents a model of solar home PV system developed using MATLAB software. Two types of solar PV modules; A Copper, Indium, Gallium, Selenium (CIGS) thin film and a polycrystalline PV module with 24V lithium nickel cobalt aluminum oxide as a storage were modeled. The Solar radiation data and load profiles were collected from Dodoma, Tanzania. In order to get optimum results, optimization tool was also developed by using genetic algorithm. For efficient operations of direct coupled PV systems, the ratio between 0.7 and 0.9 of battery to PV maximum power point voltages has been proposed. By using these ratios in PV system designing, one can have an assurance of operating PV system at minimum losses in areas with high solar radiation. This can be a simple method to be used when designing solar home system. However, more detailed analysis on battery capacity and PV modules are recommended.