Selecting a high specific speed pump for low head hydro-electric power generation

Small-scale hydroelectric power systems are emerging as a promising source of renewable energy generation, but they require low cost hydraulic and electric equipment to make them economically feasible. Using a pump as turbine (PAT) and induction motor as generator can save substantial capital investment. Recent power electronics development can produce 60 Hz electric power for a wide range of generator speeds, providing additional flexibility. Specifically direct drive systems can be operated over a range of head conditions without flow control. The selection of the correct pump for the turbine service has been difficult due to the lack of PAT performance data. This is especially true at high specific speeds. This paper presents a simple approach to predict PAT performance to aid in pump selection. A micro-hydro site producing 25 kW electric power from 5.5 meters of gross head is presented as a case study.