A photovoltaic-powered water pumping system, employing an induction motor pump, capable of supplying a daily average of 50 m3 at 37-m head has been developed. The system was installed on a desert well in Jordan, where: the average solar radiation amount to 5.5 kW h/m3/day, to provide the Bedouins living in the well area with drinking water.
A mathematical model to enable testing the system performance by computer simulation was developed. This model allows the representation of motor torque in function of speed (and slip) at different supply frequencies, as well as the flow rate and efficiency of the system in function of supply frequency and pumping head.
Prior to its installation on the desert well, the system performance, in accordance with frequency and head, was thoroughly tested in the laboratory. As illustrated in this paper, simulation and laboratory testing results are well matched. At constant pumping head, the flow rate is proportional to the supply frequency of the motor. At constant flow rate, the pumping head is proportional to the supply frequency squared only in the range below the peak efficiency of the pump. For higher flow rate values, a special algorithm based on the experimental results could be developed.
Higher system efficiency is achievable at higher frequency. It is advisable to operate the motor pump at the nominal frequency, flow rate and head corresponding to maximum efficiency. Long-term field testing of the system shows that it is reliable and has an overall efficiency exceeding 3%, which is comparable to the highest efficiencies reported elsewhere for solar powered pumps.
Source: Najah National University
Author: Abdel-Karim Daud, Marwan M. Mahmoud