Approximate formulae for the assessment of the long-term economic impact of environmental constraints on hydropeaking

The establishment of more severe hydrological environmental constraints, usually minimum flows and maximum ramping rates, on hydropower operation is a growing trend in the world. This paper presents the results of an attempt to assess the long-term economic impact of the above-mentioned constraints by three approximate formulae which quantify their effects, both separately and jointly, on a hydropower plant characterised by two parameters. The formulae are the result of three regression models developed from the solutions of 476 deterministic long-term hydro-scheduling problems corresponding to ten hydropower plants located in Spain. They were tested with 98 additional problems corresponding to two other Spanish hydropower plants. The formulae have a final average relative error of 8.2% and a final relative error of 19% with a confidence interval of 95%. This paper also offers some insight about the difficulties for tracking the energy prices when these constraints are present. Finally, the analysis of the hourly results indicates some additional effects of these constraints on hydropower operation related to the energy generated by the plant, the amount of water spilled from the reservoir, and the number of operating hours and of start-ups and shut-downs of the hydro units.