On September 1 2017, an extreme late-summer heat wave hit California and much of the west coast. The heat wave included normally temperate coastal cities in addition to inland areas. For example, San Francisco set an all-time high temperature record of 106 degrees, beating the old record by 3 degrees. In spite of this, the California ISO (CAISO) peak demand for the day still did not exceed the record peak of 50,270 MW set on July 24, 2006. In this Insight, we examine the CAISO demand and supply dynamics of 9/1/2017, focusing on the hourly performance of traditional generators and renewable technologies. We then extrapolate that information to see what it can tell us about a high renewable future in California.