Performance Evaluation of a Pump as Turbine in a Simplified Pico Hydropower System with Provision for Water Recycling

Abstract

The performance of a pump used as a turbine (PAT) in a simplified Pico hydropower system with the provision for recycling water to an overhead reservoir (OHR) 7.2 m high was investigated. A vertical PVC pipe of diameter 0.0762 m reduced into four replaceable nozzles of diameters 0.0635, 0.0508, 0.0381 and 0.0254 m was used as penstock. A 1.5 Hp surface pump was used to lift water from an underground reservoir to the OHR and the PAT was coupled to a generator by a pulley and belt drive. The volume of water discharged was monitored for each nozzle diameter till the OHR was empty, and the voltage developed and current flowing through the load measured. The flow rate, shaft power, and efficiency of the PAT for the no-load tests and then including the electrical power for the on-load tests were computed. The highest and lowest efficiency of the system (0.694 and 0.497) corresponded to nozzle diameters of 0.0635 and 0.0254 m respectively, while the highest efficiencies for each nozzle diameter (0.684, 0.629, 0.550 and 0.497) were recorded for the highest respective flow rates for the no-load tests. For the on-load tests, the highest and lowest power developed (2.976 and 2.760 kW) were obtained for the largest and lowest nozzle diameters, with the highest power for each nozzle diameter corresponding to the highest respective flow rates. These results indicate the critical role played by the nozzle diameter in producing the torque required for power generation. This confirms the critical role of flow rate and available head for determining the site feasibility in conventional hydropower practice. Overall, the results show good potential for the system to be implemented as a clean, stand-alone, small power generation unit that will enhance end-user control.