Evaluation of hydropower equivalents in electricity capacity expansion models

Journal article, 2026

As a dispatchable and flexible carbon-free generator, reservoir hydropower provides a significant value to the electricity system. However, with an expected surge in the European electricity demand and an increasing share of variable renewable generation, the role of hydropower is expected to change. Yet, in capacity expansion models, the flexibility of hydropower tends to be overestimated due to an exceedingly simplified implementation, leading to underestimations of investments in other dispatchable technologies. This work aims to improve the representation of hydropower in such models by identifying important constraints from detailed hydropower models.Three hydropower equivalents are applied to the Swedish hydropower system in an energy system model of northern Europe. It is concluded that an equivalent that captures the physical limitations of a river system is preferred, especially if grid expansion is an option within the model. The limitations pertain to not having water in the appropriate parts of the river system to facilitate sustained generation at high levels, losses due to spillage at bottlenecks, and the dispatch of water to avoid flooding of smaller reservoirs during periods with a low marginal cost of electricity. Regarding the future role of Swedish hydropower, the findings show that hydropower manages multiday variations in wind power production to a greater extent than the diurnal variations of the electricity demand.