Sunset so soon? (Catamount) Duke Energy, one of the biggest coal-burning utilities in the U.S., just added another clean-energy company to its growing portfolio. The Charlotte, NC-based company will pay $320 million for Catamount Energy Corp., a small wind-power developer based in Vermont.

There are a few possible readings here. First, maybe rising capital costs of coal and nuclear power plants�as well as rising fuel costs for coal and natural gas�really are turning the tables against traditional ways to generate power and...