Stream water wheels as renewable energy supply in flowing water: Theoretical considerations, performance assessment and design recommendations

Water wheels were the earliest hydraulic machines used in antiquity to convert water energy into mechanical one. Due to their simple installation, low maintenance costs, and thanks to the possibility to use local manpower and material for their construction, nowadays water wheels are again used as energy supply, especially in remote localities and emerging countries. In particular, stream water wheels are installed in flowing water where there are not head differences. The performance depends on the blockage ratio, so that they can be subdivided into three main categories: stream wheels in shallow subcritical flow, shallow supercritical flow and deep flow. In this paper, experimental, theoretical and numerical data on stream water wheels were systematically collected from literature and analyzed. Guidelines for their design were discussed focusing especially on wheel dimensions, supporting structures, blades and speed. More light on their hydraulic behavior was shed, adopting the previous classification for a better explanation and understanding. Results showed that in shallow water an head difference can be generated by the wheel, increasing the power output. In deep flow, accurate hydrodynamic floating/supporting structures allow the hydrostatic force of water to be exploited in addition to the kinetic energy of the flow. As a consequence, power output can improve from 0.5 to more than 10 kW per meter width, so that stream wheels can represent an attractive energy supply in zero head sites.