Energy potential assessment and design of a run-of-river hydropower plant

Abstract

The global phenomenon of climate change has forced mankind to relook at its way of living. The subsequent worldwide effort to reduce harmful emissions has resulted in a search for using more renewable energy resources to replace the non-renewable energy types such as fossil fuels in energy production. In this intensified search for more renewable energy generating opportunities, South Africa amongst many countries, launched its own renewable energy independent power producer procurement programme (REIPPPP) to create more renewable energy projects. After five bidding windows for new tenders, the country had secured 105 new projects. Under the small projects segment, multiple small projects of under 5 MW capacity were already allocated. However, the minimum cut-off capacity of 1 MW, is excluding micro and pico hydropower options. Hence this research looked at the hydropower potential at wastewater treatment plants to supplement the electricity supply. The Zandvliet Wastewater Treatment Works was selected for this research. The turbine options for hydropower at this site were evaluated and the Archimedes screw turbine was found to be the best candidate. A comparison of the energy yield was drawn between installing the hydropower scheme at the discharge point of the plant, against implementing it in the river in which the plant is discharging. The best turbine for the river was found to be the hydrostatic pressure machine. The energy of the two sites was simulated in MATLAB and the resultant energy potential of the two sites was compared to indicate the maximum possible energy generation. The results show that the hydropower scheme at the wastewater plant generates considerably more power than the scheme at the river, even with additional water flow at the river. The turbine at the wastewater treatment plant generates 7.9 kW and 9.8 kW power for a low and high-efficiency turbine respectively, while the turbine at the river produces average power of 3 kW. The potential energy yield found in this study gives authorities and prospective owners an indication if there is merit in further investigations into hydropower projects at wastewater treatment plants. If only 20% of the more than 850 wastewater treatment plants in SA have a head of 1.5 m or more, they would have a collective annual energy potential of 10.4 GWh.