The solar industry wants certainty, not approximations because a lot rides on the separation of exact from merely close. Uncertainty, or margin of error, can cost a solar module manufacturer millions of dollars. “This is over a $30 billion industry now,” said Keith Emery, a consultant to the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) and, before he retired in 2016, the point person for the laboratory’s work to measure the effic...