Norwegian hydropower has an excellent potential to balance power production in a future Central-West European power system with large shares of variable wind and solar resources. The assessment of the realistic potential for Norwegian hydropower to deliver flexibility is based on two pillars, adequate hydropower modelling and the sufficient geographical area covered in the model. Analyses are done with state-of-the-art models including a detailed description of cascaded water-courses with more than thousand reservoirs. Interoperability between hydropower and renewable energy sources is ensured as the entire European electricity generation from renewables with high geographic and temporal resolution is included in the study. To properly account for the full uncertainty of weather variables, many historic years of climate data are applied. The results show that without more flexibility in generation or demand, power prices become very volatile and show expedient periods with capacity deficit and curtailment of demand. Prices vary significantly both from hour-to-hour and from year-to-year. Increases in flexible hydropower provide large benefits to the system: significantly decreasing peak prices and reducing the involuntary shedding of demand. As short-term effects become increasingly important due to large-scale integration of renewable energy sources the correct modelling of flexible hydropower is highly important. (C) 2018 Elsevier Ltd. All rights reserved.