Modeling the Endurance of Hydropower : Assessing the impact of model constraints on the endurance of the Lule River

Sammanfattning

The increasing share of variable renewable energy in the Nordic power system is causing greater long-term variability in electricity prices and new challenges in power system balancing. Swedish hydropower, with its inherent flexibility and large reservoirs, is well-suited to address these challenges. However, the extent to which hydropower can reliably balance multi-day variations in renewable output remains uncertain. This thesis explores the role of hydropower in future energy systems and provides insight on which model constraints are important in modeling the endurance and flexibility of hydropower systems. Critical constraints are identified and modeled using Vattenfall R&D’s deterministic detailed hydropower model and the Lule River as a case study. Nine different model constraints are developed, including constraints on flow limits, spillage costs, generator start-costs, and reserved capacity of ancillary services. The measures of sustained and forced capacity are used to quantify endurance during prolonged periods of both high and low price levels. Endurance is found to be heavily influenced by model constraints, highlighting the importance of incorporating operational and environmental limitations in hydropower modeling to accurately determine endurance. The findings specifically indicate that flow constraints have the greatest impact on endurance, underscoring the role of spillage near bottlenecks in maintaining high production. While these constraints have little effect under historical prices, they become critical in scenarios with multi-day price variations. Furthermore, hydropower is shown to handle intra-day price variations much better than multi-day price variations. The inclusion of flow constraints, seasonal reservoir limits, and reserved capacity for ancillary services is found to decrease the endurance significantly. Including these constraints, the Lule River is estimated to be able to sustain 84-96% of its installed capacity for one week and 44-81% for three weeks. During a three week low-price period, the Lule River is found to have must-run volumes that amount to 4-33% of installed capacity. High intra-annual variation of endurance is found, with decreased endurance in spring and summer.