  Previous research has raised concerns about energy droughts in
renewables-based energy systems. This study explores the ability of reservoir
hydropower to sustain a high output and, thereby, mitigate such energy
droughts. Using detailed modelling, we estimate that Swedish hydropower can
sustain 67-92% of its installed capacity for 3 weeks, with higher values
possible in springtime. The variation of the sustained output, equivalent to
the capacity of 3-4 Swedish nuclear reactors, under-scores the importance of
understanding the potential output levels when devising strategies to
counteract energy droughts. Moreover, we find that regulations imposed on the
flows in river bottlenecks hinder higher sustained output levels. With the
upcoming renewal of environmental permits for hydropower plants in Sweden,
these findings provide valuable insights for policymakers. Furthermore, the
sustained output capabilities demonstrated in this study challenge the
prevalent simplified representations of hydropower in energy models, suggesting
a need for more-sophisticated modelling approaches.
