Dr. Mike Wagner is an associate professor of mechanical engineering at the University of Wisconsin Madison.  His work focuses on the optimization of renewable energy production, in particular from concentrating solar plants, in order to maximize efficiency and profitability of those systems.  We talk about how concentrating solar plants work and what advantages they offer when compared to other renewables like wind or photovoltaics.  We also discuss grid frequency and stability and how the increasing presence of variable renewable power sources is creating challenges in terms of maintaining grid frequency and stability.