Test rig development for overshot water wheels under low-head, low-flow conditions in pico-hydropower applications

Abstract

This study presents the development and validation of a controllable experimental test rig for overshot water wheels operating under low-head and low-flow conditions commonly found in pico-hydropower resources. Many potential pico-hydro sites operate at heads below 1.5 m with minimal flow, where conventional turbines often experience reduced efficiency and suitable laboratory-scale testing facilities remain limited. The developed system consists of two high-density polyethylene (HDPE) water tanks, an adjustable-inclination water channel, a circulation pump, and an overshot water wheel equipped with recyclable polyethylene terephthalate (PET) bottle blades. The test rig operates within hydraulic range of 0.525 - 1.169 m head and 0.01 - 0.02 m³/s flow rate, enabling the simulation of realistic pico-hydropower conditions. Water velocity was regulated using the water trajectory method by varying the channel inclination angle between 10° and 50°, producing velocities ranging from 1.494 m/s to 4.519 m/s. Experimental results show stable and repeatable hydraulic conditions with measurement uncertainty of approximately ± 0.03 m/s. These findings demonstrate that the developed test rig provides a reliable platform for future investigations of overshot water wheel performance parameters, including rotational speed, angular velocity, force, torque, mechanical power, and efficiency in pico-hydropower applications.