Author(s): Phoebe Pellew; Jaime Michavila; Gerald Muller

Linked Author(s): Phoebe Pellew, Jaime Michavila

Keywords: Ultra-Low Head; Hydropower; Hydrostatic Pressure Wheel; Prototype; Irrigation

Abstract: Effective use of land and water resources in agriculture is increasingly important. Additional power is required to irrigate land above irrigation canals and incorporate water-saving irrigation techniques. Hydropower potential within existing irrigation infrastructure offers an alternative to diesel generators for off-grid locations. Hydropower in irrigation canals exists at drop structures, and can be induced by introducing weirs to create a low head difference around 0.2 m to 1 m. Such ultra-low head hydropower sites are difficult to use however since standard hydropower converters are not cost-effective in this range. The Hydrostatic Pressure Waterwheel (HPW) was developed at Southampton University for ultra-low head situations. It is a straight-bladed waterwheel driven by hydrostatic pressure difference across the blades. Theory suggests that efficiencies increase with reducing head difference. Experiments have confirmed the theory with efficiencies up to 80% under laboratory conditions. Full-scale prototype tests are required to confirm the HPW as a viable hydropower converter. In co-operation with aQysta Ltd. (Delft, Netherlands), a full-scale installation was developed for an irrigation canal in Hijar, Spain. Flow rates ranged from 0.4 m³/s to 2.0 m³s/1. A 1.0 m high weir was built in the canal to generate head differences between 0.2 and 1.0 m, providing a hydropower potential of 0.6 kW to 6 kW. Whilst allowing for maximum flow during wheel shutdown scenarios, preliminary laboratory tests showed the HPW as a viable solution for this situation. A 24 bladed wheel with diameter 3.55 m and width 0.77 m was designed and installed by aQysta. The wheel powered a diaphragm pump that lifted water to a reservoir 30 m above the canal to irrigate nearby higher land. Tests were conducted in July and October 2020. Total flowrate was approximated from velocity and depth readings upstream at a sluice gate. Effective flowrate and input power were determined from RPM and depth readings up- and downstream of the wheel. Output power was calculated from readings of pressure, flow rate and head loss within the pump network. During testing, total flow rates recorded were between 1.1 m³s/ and 2.0 m³/s, with effective flow rates through the wheel of 0.1 m³/s to 1.0 m³/s and head differences from 0.18 m to 0.92 m. The power output ranged from 0.655 kW to 2.068 kW, with efficiencies of 60 to 80%. The site tests showed the HPW allowed for the effective use of head differences as low as 0.18 m. The HPW performance reflected the theory and laboratory results, indicating the validity of theory and small-scale tests as design tools. Design improvements were identified to increase the proportion of the flow through the wheel, and improve overall installation efficiency. The HPW was found to be an effective technology for ultra-low head hydropower.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221049

Year: 2022