Exelon (EXC -0.62%) is one of the largest power companies in the U.S., and the largest provider of nuclear power in the nation. Investors in this company could see a major upside, but there are key metrics to be followed and understood, to know when is the right time to buy. In this video, Motley Fool energy analyst Taylor Muckerman tells us how low natural gas prices are a continued threat to Exelon's margins and how, when those prices come back up, the gains could be huge. He also discusses the company's recent exposure to more competition, and the continuation of government subsidies for renewable energy sources, which may mean even further competition from renewables like wind energy.