Modernising RoR Hydropower: A Study on Retrofitting Aged Turbines for Optimal Performance

Hydropower stands out as an economical, reliable, sustainable, and renewable source of energy. It has been the leading source of renewable energy across the world, generating more than 15 % of total electricity in 2022. Therefore, it will likely play a crucial role as the energy system shifts towards a carbon-free future. The turbine system is at the heart of the hydropower plant and converts flowing water into mechanical energy. Remarkably, around 154 gigawatts, or one-fifth of the installed hydropower turbines, will be more than 55 years old by 2030 globally. Modernising these aged turbines is essential for sustaining optimal plant performance and this will create opportunities to retrofit hydropower facilities to improve their adaptability to changing hydrological conditions. A well-defined methodology is necessary to evaluate feasibility and select optimal solutions for upgrades. 

This study addresses this critical necessity in the context of run-of-river (RoR) hydropower plants with the HYPER_OP toolbox to efficiently evaluate and choose optimal turbine replacement or upgrade options. HYPER_OP provides operational optimization capabilities coupled with design flexibility and expanded simulation features for complex turbine configurations. It facilitates the selection of turbine systems featuring large and small turbines. The effectiveness of this toolbox is illustrated through the  case study of the Bonnington RoR hydropower plant, commissioned in 1927 on the upper reaches of the River Clyde in Scotland, United Kingdom. Bonnington RoR features a pair of two identical Francis turbines, each designed for a discharge of 12 m³/s and equipped with an installed capacity of 5.5 MW.

Our analysis indicates that, by prioritising Net Present Value (NPV) maximisation through a single objective function and considering historical discharge records, HYPER_OP offers a novel configuration featuring non-identical Francis turbines with design discharges of 16.13 and 9.13 m³/s.  Optimal design increases power production by approximately 3.4 GWh (~7 %) annually by providing operational flexibility and retaining high efficiency over a range of discharge values. The optimal design yields an NPV of approximately 3 million dollars (USD), factoring in the additional energy increase as revenue, turbine replacement cost, and lifetime operation cost. The payback period for this investment is projected to be 15 years when considering only the additional energy as revenue. It's worth highlighting that the optimised design notably outperforms the current configuration, particularly in response to variable streamflows, including both high and low flows. Therefore, optimal design is expected to be less vulnerable to climate change due to higher efficient configuration.