Renewable energy sources like wind and solar generation now account for over 20% of electricity in the U.S. — and keep growing after large-scale production more than doubled since 2000. Still, high-profile power failures illustrate persistent challenges from the lack of available capacity to provide enough energy at times of need, said Chiara Lo Prete, an associate professor of energy economics in the John and Willie Family Department of Energy and Mineral Engineering at Penn State.

Doctors may be able to spare patients unnecessarily aggressive breast cancer treatments by collecting and testing cancer cells in patients' blood, research from the University of Michigan and the University of Kansas suggests.