Effects of the maximum flow ramping rates on the long-term operation decisions of a hydropower plant

Abstract

This paper presents a study on the influence of maximum ramping rates (MRR) on the annual operation of a real hydropower plant. For this purpose, an annual optimization model based on incremental dynamic programming (IDP) with weekly steps is used, each step being evaluated by mixed integer linear programming (MILP) on an hourly basis. The model considers hourly water inflows and energy prices, limits on reservoir level and water discharge, power generation dependence on the available head, wear and tear costs of hydro units caused by power variations, start-up and shut-down costs of hydro units, and minimum environmental flows and maximum ramping rates. The main contribution of the proposed model is the consideration of the released flow as a second state variable to define the state diagram of the problem, with the aim of guaranteeing the continuity of flow between consecutive weeks and thus the fulfilment of MRR. The results obtained in a case study with a real plant are discussed. The inclusion of the released flow as state variable does not show a significant impact in the estimated annual revenue, but certain differences observed in some periods of the year might justify its consideration in shorter time horizons.