PNNL

Abstract

Thermoelectric power plants often depend on multipurpose reservoirs to supply cooling water. Although reservoirs may help buffer natural hydrologic variability, severe droughts can deplete storage below critical thresholds, or to levels at which the effluent water temperature becomes too high to meet the environmental compliance requirement for cooling. This study explores the effects of projected climate change and drought events on water storage at 30 major reservoirs that collectively provide cooling water for about two thirds of thermoelectric power capacity in the Electric Reliability Council of Texas (ERCOT) power grid. Multi-ensemble future runoff projections generated from eleven downscaled hydroclimate simulations are mapped to key watersheds to create spatially correlated multi-reservoir inflow sequences. These data are used to drive reservoir operations, which are linked to an industry-adopted metric of “thermal capacity at risk” using critical thresholds intended to represent storage volumes below which generation could become severely disrupted. The projected impacts of climate change are mixed, with results indicating an increase in the occurrence of widespread thermal disruption under only half of climate models, while three models project reduced occurrence of widespread thermal disruptions. A critical threshold of 30% storage volume—applied to all reservoirs—results in disruption to about one fifth of ERCOT thermal generation during a small number of severe projected droughts. The study highlights an important role for detailed reservoir behavior simulations for better understanding the effects of drought and climate change on thermoelectric plant performance. Site-specific reservoir specifications, including intake levels and withdrawal and effluent temperature limits, are required to enhance results with quantified, plant-specific thermoelectric derating impacts associated with simulated droughts.