The Western Wind and Solar Integration Study (WWSIS), released yesterday by the National Renewable Energy Lab, proclaims the good news: integration of 30% wind and 5% solar is “feasible” in the west. There are some minor caveats, notably a dramatic increase in forecasting accuracy along with increasing generator scheduling granularity from hourly to several times an hour. Conspicuous in absence is the lack of extensive discussion on the role of energy storage for regulation. (The authors admit, in the most conditionalized language possible, that “Energy storage may be a cost effective alternative to generation options for providing regulation and load following. Detailed subhourly analysis of storage was not performed, but could warrant further investigation.”) If WWSIS authors had considered previous work, they may have found that existing energy storage technologies could have mitigated the minor hiccups in the study at dramatically lower costs than traditional generators. The WWSIS study is a sturdy piece of work, but it should be considered a worst case scenario. Storage will enable 35% renewables with even fewer hurdles.