Abstract
Implementation of EU’s Water Framework directive, meant to ensure sustainability of the hydropower production, may lead to new environmental constraints on hydropower systems. This can result in loss of production, reduced operational flexibility and consequently reduced income from production. Flexibility is here defined as the ability to adapt production to variations in power prices, whereas the production income is strongly influenced by the price level and sum production. This paper presents and evaluates two different measures that are used to quantify how new constraints affect system flexibility in the Norway and Sweden. These measures are the established Flexibility Factor, comparing achieved price with average price, and an imaginary equivalent electrical storage unit, which is parametrized by the equivalent storage and power capacity needed to compensate for the lost flexibility. The calculation and evaluation of the two measures are exemplified using two Norwegian water courses.