A recent National Renewable Energy Laboratory (NREL) report noted that wind and solar, despite being intermittent sources, could supply 30% of the annual power for the Eastern grid without increasing reliability concerns. Noting that wind and photovoltaic are the fastest growing electricity sources in the U.S., the authors determined that “under the study assumptions, generation from approximately 400 GW of combined wind and PV capacity can be balanced on the transmission system at a 5-minute level.” However, despite what many renewable energy advocates would consider to be good news, it was also clear that to do so would mean much more frequent start-ups and shut downs of fossil fuel plants – activities that can put stress – and increase maintenance costs – on these facilities. That said, the authors also left demand response and storage solutions out of their assumptions, which could increasingly counterbalance potential negatives of an increasingly green energy supply mix. The study itself can be found here.