As weather dependent renewable generation grows, it is important to understand the covariance of renewable resources and load. In a power grid with a high penetration of renewable energy, periods of high system risk no longer correspond only to peak hours. In particular, high renewable energy complicates the stress extreme weather events already place on the grid, and it shifts what types of weather conditions are most problematic. Accordingly, reliability assessments in long-term planning studies may change dramatically in the coming years. This may impact how utilities and grid operators assess reliability in long-term planning. Weather that stresses grid resilience typically does so by creating peak loads across a broad region, at the same time as placing constraints and increasing outage potential for transmission and generation. Two examples are cold snap event like the “Polar Vortex” of January 2014 and extreme heat events like that which the Southwest United States experienced in June 2017. The Extreme cold weather event saw record low temperatures extending from the northern tier states all the way to the Gulf coast, which led to extreme heating loads and the forced outage of conventional generators in states where generating plants were ill equipped to deal temperatures.
