Radial- and mixed-flow turbines for low head microhydro systems

This paper describes the design of two different specific speed microhydro turbines operating at heads between 6 and 12 m, at small scale and up to heads of 50 m at larger scales. The features are specifically tailored for ease of manufacture and uniquely resistant to debris blockage. Test machines are described and test results given; hydraulic efficiencies of over 70% have been achieved in all test models despite the fact that the turbine blades are made from flat plate, specifically to simplify manufacture. Outline drawings are given with key dimensions for each reference model, along with the equations for scaling to arbitrary sizes. These turbines are the mixed- and radial-flow members of a family of turbines developed to cover the microhydro range from 2 to about 50 m of head, which is below the range where Pelton wheels are applicable.