As global energy demand rises, the need for sustainable and flexible electricity production grows. Renewable sources like wind and solar are crucial for reducing carbon emissions, but their variability creates challenges for the stability of the power system. Hydropower plays a key role in balancing these fluctuations by quickly adjusting its production. In response to new European Union regulations, Sweden is currently evaluating and imposing environmental restrictions on its hydropower plants. This study analyzes the operational flexibility of hydropower plants under these environmental constraints on the Ume River, using a metric called Equivalent Energy Storage (EES). The EES results are compared to other flexibility metrics, including Flexibility Factor (FF), Modified Flexibility Factor (MFF), and the Stress Test. Flexibility was evaluated using operational data from May 2023 and November 2016. The results for EES indicate that environmental constraints negatively impact the flexibility of hydropower plants. Specifically, stricter constraints require larger EES values to compensate for the loss of flexibility. The EES metric aligns well with MFF results but diverges from FF and the Stress Test in the minimum spillage scenario. While EES and MFF indicate reduced flexibility under minimum spillage constraints, the Stress Test remains unchanged, and FF results are ambiguous.
Feldman et al. (Wed,) studied this question.