A Simulation-Optimization Model for Cascade Multi-Reservoir Hydropower Systems Operations

Sequential streamflow routing (SSR) with control on reliability of meeting energy demand is a common method for assessing energy potential in practical hydropower projects' design and operation in Iran. This approach results in developing a reliability-based simulation (RBS) model which is used for design of single- reservoir hydropower projects. On the other hand, in most cascade hydropower systems in the country, a single-reservoir RBS model is usually used for design and operation of each reservoir, independently. Considering the fact that the integrated analysis of the system may lead to design variables and system energy potential which could be different from those obtained by subsequent single-reservoir analysis, a multi-reservoir simulation-optimization model is proposed considering the integrated system operations. The core of the model developed is the same as what is used in a single-reservoir RBS model as a simple and well-known model in professional applied hydropower practices. However in multi-reservoir RBS model, the energy equation in each time period becomes indeterministic with more than one unknown variable, i.e. turbine releases. Therefore, an iterative single-period linear programming (LP) model is used in each time step of the simulation model. The LP model minimizes the sum of reservoir releases and/or maximizes the sum of reservoir storages subject to continuity equations, minimum energy demand requirement and bounds on state and decision variables as model constraints. Another multi-reservoir model was also tested in which a heuristic operating policy is used. The application of the above-mentioned models is analyzed in the Khersan hydropower reservoir system located in Iran as the case study. For reliability of meeting energy demand equal to 90%, results indicate that the multi-reservoir RBS model proposed increases the system firm energy by 7.9% compared to the model which sequentially uses single-reservoir RBS models.