Wind and Solar Droughts over western North America

Abstract:

Wind and solar electricity generation is projected to expand substantially over the next several decades due both to rapid declines in their costs as well as legislation passed in the service of climate and sustainability goals. With increasing reliance on wind and solar generation, future energy systems will have the potential to be sensitive to previously underappreciated variations in near-surface wind speed and surface solar radiation. Even energy systems that incorporate long-distance electricity transmission and sufficient energy storage to buffer the daily solar cycle will still be vulnerable to synoptic-scale (several thousand kilometer spatial scale and several day timescale) events characterized by low wind and/or surface solar radiation – wind and solar droughts. Here, we use western North America (WNA) as a case study region to investigate the typical meteorological causes of wind droughts, solar droughts and compound wind & solar droughts. We also investigate the covariability between wind and solar droughts and potential changes in energy demand via heating and cooling degree days. We find that wind droughts tend to occur in late summer and are characterized by a mid-level ridge over British Columbia and high sea level pressure on the lee side of the Rockies. Wind droughts are associated with reductions in both heating and cooling degree days. Solar droughts occur near winter solstice when the seasonal minimum in incoming solar radiation combines with a pattern of low pressure off the west coast of WNA which advects warm moist air and causes cloudy conditions over the U.S. southwest. Solar droughts are associated with reduced winter heating degree days. Compound wind & solar droughts largely consist of the aforementioned meteorological set up of wind droughts occurring near winter solstice. They are associated with cold conditions and thus increased heating degree days. We find that wind droughts are associated with solar surpluses (and vice versa) both seasonally and in terms of synoptic meteorology, which supports the notion that these energy resources can be utilized as complements in a diversified energy portfolio. Studying these events from a meteorological perspective should help facilitate their prediction as well as inform studies on how they might evolve under future global warming.