Retrofitting Reservoir-Based Hydropower Plants: Turbine Upgrades for Enhanced Efficiency and Resilience

Hydropower plants are the primary source of renewable energy globally, but their performance and reliability naturally degrade over time due to aging equipment, changing environmental conditions, and shifts in operational demands. By 2030, nearly 20% of global hydropower turbines, totaling about 154 GW, will be over 55 years old, while in the United States, the average turbine age will exceed 60 years, leading to significant efficiency challenges.

Retrofitting aging hydropower plants is crucial for ensuring optimal performance and offers opportunities to improve the adaptability of these plants to changing conditions. Traditionally, retrofitting has relied on identical turbine replacements, with newer models replicating original designs optimized for the conditions at the time of construction. While these upgrades offer marginal efficiency gains, they fail to address evolving challenges, as original designs may become suboptimal in the face of a changing climate and evolving grid demands. Given that these turbines are expected to operate for 40 to 50 years in an increasingly uncertain future, adopting turbine designs optimized for future conditions presents a more effective solution. To guide this transition, a well-defined methodology is needed to determine when and how to upgrade turbines, ensuring optimal and sustainable outcomes.

This study addresses this need for large-scale hydropower upgrades by using a newly developed toolbox to determine optimal turbine replacement strategies under uncertain inflow, demand, and energy price scenarios. It combines multi-objective optimization and advanced simulations for detailed comparisons between existing and optimized turbine configurations. The optimization focuses on maximizing capacity during peak demand, enhancing energy generation across fluctuating reservoir levels, addressing risks and costs associated with aging turbines, and ensuring efficient operation under low-flow conditions to support environmental releases. The toolbox is applied to the Hoover Hydropower Plant (HPP) in the Colorado River Basin, which operates 17 Francis turbines installed in 1936. These turbines were initially replaced with identical models around 50 years later (1986–1993). However, by 2012–2015, declining reservoir levels made the original turbines inefficient, leading to the replacement of five turbines with lower-head models, a rare example of non-identical replacement to adapt to changing conditions.

Preliminary results from a retrospective analysis of Hoover HPP highlight the benefits of optimizing replacement strategies. Optimized configurations across multiple objectives generally recommend (1) earlier turbine replacements to reduce efficiency losses (2) lower-head turbines to accommodate fluctuating reservoir levels especially due to droughts, (3) require a lower number of turbine replacement overall while increasing annual energy generation.