New Technology to Increase Hydropower Plant Operational Flexibility

In this paper a new way has been suggested to address operational restrictions in hydro power plants with outlet to rivers by a technical installation called “Air Cushion Underground Reservoir”. This is an excavated, air pressure regulated storage volume for the water in connection with the tailrace tunnel. ACUR has been designed to control the net flow into the river, making it possible to address today´s environmental restrictions but significantly increasing operational flexibility because power generating flow through the unit and discharge to the river is temporarily decoupled. Also, this system can be utilized to control pressure waves and store excess liquid in the hydropower plants as a closed surge tank system. To evaluate impact of this system on the hydroelectric power plants and rivers, the Norwegian river Nidelva, and the power plant Bratsberg has been selected and modelled with different scenarios. The results confirm that the ACUR can decouple the production flow and the discharge to the river, increasing operational flexibility while still providing the required environmental flow.