100% renewables doesn’t equal zero-carbon energy, and the difference is growing

“To guarantee 100 percent emissions reductions from renewable energy, power consumption needs to be matched with renewable generation on an hourly basis,” said Sally Benson, co-author of the paper and co-director of the Precourt Institute for Energy. “In California, gas is often the marginal generation source and has a higher emissions rate than average grid power, which is why purchasing renewables can result in a net negative carbon footprint,” said de Chalendar. By using its energy storage to maximize purchases of electricity in the afternoon when solar power dominates the California grid, Stanford could reduce emissions from heating and cooling by an additional 40 percent, according to a study published earlier this month by the authors of this paper.

Source: energy.stanford.edu