Residential solar in the U.S. grew 66 percent in 2015 over 2014, the largest annual growth rate to date, according to a recent report by GTM Research and the Solar Energy Industries Association, or SEIA. In 2015, residential solar installations amounted to 2,099 megawatts, which, when converted, equals more that 1,600 megawatts. By comparison, Montana's coal-fired Colstrip plant, the second-largest power plant west of the Mississippi River, has a peak output of 2,100 megawatts. The International Renewable Energy Agency reports that between 2010 and 2015 the cost of solar photovoltaic panels dropped 80 percent, fueling the solar surge around the world.
Forty-one states and the District of Columbia have mandatory net-metering rules, but the rapid growth in residential solar has states from New York to Montana wrestling with how to promote this renewable, distributed resource in a way that placates utilities challenged by integrating the power and apportioning the associated costs. Nevada, for example, the fifth-largest residential solar market in 2015 with 17,000 producers, recently implemented drastic changes to its net-metering policy that the Alliance for Solar Choice, in challenging the decision in court, called "a stake in the heart of future rooftop solar development." The crux of the debate is how much net-metered customers should be credited for putting excess energy onto the grid. Utilities and renewable energy advocates clash on cost-benefit analyses.