Hard-coupling of water and power system models increases the complementarity of renewable energy sources

Multi-sector modelling frameworks are fundamental platforms for exploring the complex interactions between the water and energy sectors. While acknowledging the pivotal role of hydropower within the energy system, it is essential to understand the feedback mechanisms between power and water systems to guide the design of hydropower operations and enhance water-energy management strategies. Here, we developed a novel modelling approach that hard-couples a reservoir system model and a power system model. The two-way dynamic feedback mechanism between the models allows for operational decisions to be made contingent upon the states of both water and energy systems. Operating the system as a whole offers flexibility in managing the physical storage of hydropower reservoirs to buffer the variability in other renewables, such as wind or solar. We evaluate the framework on a real-world case study based on the Cambodian grid, which relies on hydropower, coal, oil and imports from neighboring countries. In light of the country’s plan to further decarbonize its grid, we tested the framework on three grid configurations, the as-is grid, and the grid with two different levels of installed solar. To evaluate the effects of hard coupling, the experiments were simulated with and without feedback, and external inputs were varied with 1,000 stochastic generations of streamflow, solar and load. As demonstrated in our results, hard-coupling the water and energy systems brings benefits such as reduced operating costs, and boosts decarbonization efforts by supporting the integration of renewables in the grid. The two main external factors that determine the effectiveness of the feedback mechanism are streamflow and load. Under favorable conditions (large reservoir inflow and low electricity demand), the system experienced a 44% saving in annual operating costs and 53% reduction of CO₂ emissions. A spatio-temporal analysis on the reservoir operations and transmission line usage reveals that the timing of the monsoon and interconnections between the grid components also play significant roles in influencing the system’s responses to the hard coupling. Overall, our modeling framework paves way for optimized operations within the water-energy nexus. By accounting for the interdependencies between the reservoir and power system, a more efficient operating scheme for hydropower reservoirs can be derived, leading to greater complementarity of renewable energy sources.