A novel method to determine the optimal operating point for centrifugal pumps applied in photovoltaic pumping systems

Abstract

Every centrifugal pump has an optimum efficiency duty point, known as Best Efficient Point (BEP), which is usually specified by the manufacturer. In conventional pumping systems, the centrifugal pump must operate at the rated speed and as close as possible to the BEP for optimal performance. This design approach, based on the BEP concept, is suitable only when the centrifugal pump is supplied by sources that can maintain the pump’s operation at the rated frequency (50 Hz or 60 Hz) and voltage (220 V or 380 V). In photovoltaic pumping systems, the conventional centrifugal pump works at different speeds according to the availability of solar irradiance. Therefore, the BEP concept does not offer the best performance in terms of efficiency. This paper presents a method to determine the operating point that provides maximum efficiency for a given photovoltaic pumping system composed of a conventional centrifugal pump driven by a power control system. This point, referred to as Solar Best Efficiency Point (SBEP), is calculated considering the entire operating range of the pump for a given irradiance and photovoltaic cell temperature profile. According to the results, the SBEP operation, compared to the BEP operation, can increase the daily efficiency of the photovoltaic pumping system by up to 6.7%, depending on the centrifugal pump used. Furthermore, the theoretical approach developed in this paper shows that the selection of the motor-pump set cannot be based solely on the pump’s characteristics, as the motor quality significantly influences system performance.