Design and performance evaluation of a pump-as-turbine micro-hydro test facility with incorporated inlet flow control

In the context of micro-hydro power schemes the initial cost of conventional Francis turbine units is often prohibitive. As such there is growing interest in pump-as-turbine (PAT) technology offering a more cost effective, yet still highly efficient, power generating alternative, finding uses in remote area power supply and energy recovery systems. However, the implementation of a PAT is highly problematic in terms of predicting the installed best operating point coupled with poor off-design performance due to the fixed geometry and absence of inlet flow control. In the current work a micro-hydro test facility and turbine unit is developed utilising a commercially available pump impeller together with a customised housing for incorporation of inlet flow control. Working initially from established PAT theory, this paper presents the design and performance testing of a hydraulic turbine unit suitable for use in rural micro-hydro, and energy recovery installations. Maximum efficiency of the unit was found to be 79%, marginally higher than that of the parent pump, while the off-design efficiency offered considerable improvement over previously published data of traditional PAT systems. The design provides a cost effective power generator in comparison to small scale Francis turbines, while providing a greater operational range than traditional PAT units.