Critics say that regulated utilities often default to building gas plants because it’s a familiar technology and because, in many states, they earn a guaranteed profit from capital projects. They don’t always have the same incentive to adopt energy-efficiency programs that reduce sales or to plan transmission lines that can import cheaper wind power from elsewhere.

“The big utilities are typically most comfortable with one way of doing things: building those big, conventional power plants,” said Heather O’Neill, president of Advanced Energy United, a trade group representing low-carbon technology companies.

There are other ways to meet rising demand that require burning fewer fossil fuels, some experts say. Utilities could get more creative about helping customers use less electricity during peak hours or make better use of batteries, reducing strains on the grid. Advanced sensors and other technologies could push more renewable energy through existing transmission lines. Some utilities are pursuing these options, but many are not.

Over the coming months, environmentalists and other groups aim to challenge utility plans at state regulatory proceedings. In some cases, they’ll argue that the utility has overestimated future demand growth or neglected alternatives to gas. While these debates can get technical, they could have a significant impact on the nation’s energy future.

The tech companies and manufacturers that are driving up electricity demand could also play a big role. Many firms have pledged to use clean electricity for their operations, and it remains to be seen how hard they actually push power companies to provide it.

“A big question,” said Brian Janous, a former vice president of energy at Microsoft who now focuses on ways to clean up the grid, “is how much outside pressure utilities and state regulators will face to do things differently.”