Upgrading of Hydropower Plants to Pumped Storage Plants: Tunnel System Hydraulics

Abstract

Energy storage is needed to enable the transition from fossil to renewable electrical energy sources. As wind and solar power are unregulated and volatile, energy storage is necessary. Pumped hydro can deliver both short- and long-term electrical energy storage. The motivation of this work is to enable cost-efficient and more environmentally friendly construction of pumped storage plants, by finding solutions to the technical challenges. This thesis presents research on hydropower tunnels for pumped storage plants with multiple surge tanks that resulted in three journal papers. This thesis is organized to answer the following four research objectives: (1) Review of existing Norwegian pumped hydro: design challenges, technological solutions, and operational experience. (2) Verify hydraulic scale modelling for investigations of reconstruction of HPPs to PSPs. Demonstrate on a case-study. (3) Identify main challenges associated with the upgrade in terms of tunnel system design and provide solution alternatives. (4) Assess the effect of brook intakes on mass oscillations stability, and its implications for upgrading of hydropower plants with brook intakes. The three research methods applied to answer the research objectives are: field measurements, 1D numerical simulations, and hydraulic scale modelling. Much of the work is conducted based on a case-study, namely the 50 MW Roskrepp hydropower plant located in southern Norway. A feasibility study for reconstructing this HPP to a PSP is currently undertaken by the power plant owner Sira-Kvina kraftselskap, making it an ideal case-study for the work. The power plant owner granted access to conduct field measurement during operation, a 3D scanning of the tunnel system, and available documentation and reports. The work results in three journal papers, presented in this thesis. In addition, four secondary papers are published. The main contributions from this work are: 1. A technical review of currently existing Norwegian PSPs. This review provides a foundation for future development of PSPs. 2. A new method for determining the distribution of head loss factors in hydropower tunnel systems with multiple surge shafts. 3. Identification of the main limitations for upgrading HPP to PSP and provided solution alternatives. 4. An investigation of the effect of brook intakes on the stability of mass oscillations in existing hydropower plants. It is concluded that it is possible to upgrade existing hydropower plants to pumped storage plants by using the existing tunnel system infrastructure with minor modifications. Suggestions for future work are included at the end of this thesis.