Optimization of wind power generation to minimize operation costs in the daily scheduling of hydrothermal systems

This paper assesses some important economic issues that arise with increased wind power penetration in hydrothermal systems. It is shown that it may become necessary to restrict the injection of wind power into the grid to reduce the total operation cost, even in predominantly hydro systems which are very suitable to offset the variability in wind power. In the approach applied in this paper for the Daily Operation Scheduling (DOS) of hydrothermal systems, although wind power plants are designed to be dispatched with priority as compared to other sources, their power injection into the grid is not mandatory. Thus, the level of generation of each wind power plant becomes one of the decision variables of the optimal system generation dispatch, and therefore wind can be curtailed not only due to feasibility requirements, but also to obtain a more economic operation. The DOS problem is solved via Mixed-Integer Programming, considering the unit commitment constraints of thermal generating units and many operational constraints of hydroelectric power plants, in addition to the representation of the electric grid. A system based on the IEEE Reliability Test System (RTS) was used, with real data from wind, thermal and hydroelectric power plants of the Brazilian power system. The results show that restricting the injection of mandatory wind generation into the grid can reduce the total operation cost, even when the hydro share in the generation mix is high. In addition, the economic benefits of storing energy in pumped-storage hydroelectric plants to consume the surplus wind energy in this hydro-dominated context are also assessed.