Reliability Implications of Riverflow Variations in Planning Hydropower Systems

The variability and uncertainty with river flow characteristics in hydro-dominant power systems create considerable challenges in planning adequate generation capacity to maintain a target level of reliability. Unlike other firm capacity generation sources, hydropower sources are energy-limited by seasonal and climactic variability in water restrictions. These utilities face energy wastage caused by water spillage during high inflow season or low load period of the day. On the other hand, they have inadequate generation capacity to meet the load during peak load period or low inflow season. It becomes very important for hydro dominant utilities to properly manage and utilize their water resource to maintain or enhance the system reliability. Energy-based utilities are also concerned on the suitable reliability criteria they should use to fully capture energy management based on hydrological characteristics. This paper presents reliability models of run-of-river and large storage-type hydro plants to recognize their energy and capacity characteristics and proposes a methodology to incorporate water management strategies for reliability enhancement of hydro dominant power systems. The usefulness of NERC recommended reliability criterion in energy-based hydro dominant system has also assessed and discussed in the studies. The reliability impacts of proposed methodology with river flow variations, load uncertainty and maintenance schedule coordination with load levels and inflow restrictions are evaluated using the IEEE Reliability Test System that is modified to create a hydro dominant system.