Conjunctive operation of hydroelectric and thermal power-plants

An integrated approach combining deterministic dynamic programming and simulation models has been developed and applied to determine the optimal operation policy and performance of a mixed hydrothermal power system consisting of a reservoir, and several run-of-the-river hydroelectric and thermal power plants. The objective of the Optimization model is to maximise annual firm energy generation while treating the outputs of the run-of-the-river and thermal power plants as parameters. Simulation of the combined system is based on a standard operating rule, imposing an additional constraint of target demand derived from the dynamic programming model. Stochastic behaviour of the system is considered implicitly by introducing synthetic flows. Comparison of combined and separate operations of the reservoir with the run-of-the-river and thermal power plants shows that combined operation is advantageous. For the investigated system in Nepal, combined operation improves the output by 26%. The target demand of 1226.7 GWh is satisfied with a mean overall reliability of 98.8%, a dry season reliability of 97.2%, maximum deficit of 5.6%, and average maximum number of consecutive failure months of 4.2.