Monitoring and Evaluation of a Direct Coupled Photovoltaic Pumping System

In this research, a direct coupled photovoltaic (DCPV) pumping system has been monitored and evaluated in order to assess energy losses due to mismatching between the photovoltaic (PV) array and the pump motor and to identify the errors associated with traditional procedures used for PV system sizing. The pumping system under study included a 12VDC, 94W PV module and a 12VDC, 7A, positive displacement 3-chamber diaphragm pump. The most common sizing method for this kind of system uses the monthly average of daily solar radiation to estimate energy generated and water pumped. To assess the above mismatching and errors, the actual PV energy converted to mechanical work in the PV pumping system was compared to the hypothetical energy converted by the system when working at the maximum power point (MPP), and to the theoretical energy predicted by the equations commonly used to size PV systems. The PV pumping system was installed at University of Concepcion in the central part of Chile and a data acquisition system was designed and implemented to measure the energy generated and water pumped. Analysis of 17 days of data showed that the most common sizing method for PV pumping systems estimated that only 84% of the energy would be available compared to operating the PV array at its maximum power point. Additionally, the most common sizing method overestimated by 15% the energy converted into useful work by the load.