Coal-producing states like Kentucky are warily eying federal regulations that have begun moving the country away from fossil fuels.

Even so, Sue Tierney says she thinks coal will be around for awhile, though it will be cleaner and make up less of the nation’s energy mix. Tierney was the Assistant Secretary for Policy in the U.S. Department of Energy under President Bill Clinton. She’s giving a talk on what she calls “sustainable energy” in both the U.S. and China next week.

“I think of sustainable energy as a category or a way to categorize energy supplies as highly efficient, a relatively light footprint on the environment, provides a way for people to have affordable energy supplies over time,” Tierney said.

Renewable energy is getting closer to being sustainable, she says, because over time it will likely become more affordable. But Tierney’s definition of sustainable energy also doesn’t preclude fossil fuels like coal and natural gas.

She says that’s a pragmatic approach.

“The major countries of the world have enormous fossil fuel endowments,” she said. “We have to get to a point where we are including fossil fuels in a lighter way from the point of view of issuing greenhouse gas emissions.”

Tierney says that means furthering research and development for technology like carbon capture and sequestration.

But that also means using energy more efficiently. Right now, a lot of energy is wasted. And Tierney says that’s partly because there aren’t sufficient incentives for people to conserve energy. Those incentives could mean higher rates—because the more electricity costs, the less many people will use. But Tierney says it doesn’t necessarily mean higher bills.

“People where I live, which is Boston, have very high electricity rates, especially compared to people in Kentucky,” she said. “But over the years, we’ve had much bigger economic incentive to tighten our belts—to tighten up the windows, to put in light bulbs that are more efficient and so on.”

Because of that, Tierney says the average residential electricity bill in Boston is actually lower than the average residential bill in parts of the country where electricity rates are lower.

Tierney will also discuss Chinese energy development in her talk next week. She says China is investing more in cleaner energy sources than the United States is.

“[China has] been able to set high targets for adopting renewable energy, set high targets for reducing energy use in their major industries, including really heavy industry,” she said. “So they’re getting very efficient and they’ll really banking on some of these new technologies having markets globally.”

Of course, Chinese power plants are still burning a lot of coal, and as air pollution there grows worse, Tierney says Chinese scientists are increasingly interested in developing ways to burn coal more cleanly.

Tierney’s visit is sponsored by the World Affairs Council of Kentucky and Southern Indiana. She’ll speak at the Green Building on Monday evening at 6:30. Tickets are available on the World Affairs Council’s website.