Next, they must answer questions about dispatchability, or rapid demand-response; intermittent- generation technologies; economic viability when tax credits expire; and the technologies' ability to serve load without a costly combustion-turbine backup.

Despite its dwindling share, coal remains an important energy source, provided the emissions from combustion can be mitigated. The EPA's proposed powerplant rule to reduce emissions from coal plants is based on the idea that carbon capture and sequestration technology is feasible at commercial scale.

By fits and starts, perhaps more despite Washington's influence than because of it, a U.S. energy policy seems to be emerging at last. In the following pages, you will see how engineers get superior combustion from old powerplants by adding natural-gas capability, how an independent power producer is responding to current conditions, and how solar and wind power are becoming more significant parts of the mix.