Operation dependent costs of non-optimal hydropower production : Effects on the operational pattern of the Small Lule River

Abstract: In the present electrical market there is an increasing penetration of intermittent energy sources. Several studies have examined its effect on the planning of hydropower operation and the conclusion is that an increasing intermittent production is likely to result in a more variable hydropower operation, utilising a wider span of operational set points. The wear of a hydropower unit is generally at a minimum when operated close to best efficiency and increases when operating at higher or lower set points. This study introduces a method to calculate an operation dependent cost (ODC) function for an arbitrary hydropower unit or unit combination based on vibration measurements and operational data. The method is tested in a case study where an ODC is implemented in Akkats, located in the Small Lule River in order to evaluate its effect on operational pattern, profitability and balancing contribution. The results show that the implemented ODC mainly affects Akkats. For an increasing ODC, Akkats is operated closer to the best point of efficiency and the operational pattern gets less variable and the effect gets more apparent the lower the spot price. Akkats ability to follow the spot price is reduced, decreasing the earning per produced energy with a few percent­ages. Akkats balancing contribution decreases significantly more, due to a less variable operational pattern. The study compares the reduced ODC to the reduced spot income and concludes that the wear cost in Akkats has to be above 1,21 €/MWh in order to be economically feasible to include in the planning. The operational pattern for the simulated river is close to unchanged at highest price hours but during lower price hours an increasing ODC results in an increased production, due to an increasing mean flow and changed operational pattern in Akkats. More production during low prices hours results in a decreasing profitability for all plants along the river. The balancing contribution is close to unchanged in all plants except Akkats, since the production still follows the same pattern.