Ethanol, biodiesel, and wind power hog the attention when it comes to alternative energy these days. But a new report finds there is enormous untapped potential for geothermal energy, in particular around the Pacific Rim, and anywhere else there's been volcanic activity.

Unlike solar or wind power, heat from the rocks is always on. A recent report from the Massachusetts Institute of Technology, MIT, concludes that the geothermal option has been undervalued as a way of meeting future energy needs.

Geothermal power is at work in Boise, Idaho, on the western slope of the Rocky Mountains. Around town, furnaces are gobbling up fuel to heat buildings and keep occupants warm. But 55 downtown buildings share a hidden secret: cheap heat from deep beneath the earth. Geothermal engineer Kent Johnson says most people have no idea that is where the warmth is coming from. "It's interesting talking to people that I know work downtown. I'll say, 'Oh, you work in one of our buildings that is one of our geothermal customers.' They go, 'Oh, really?'"

Idaho's capital city is home to the oldest geothermal central heating system in the U.S. The first distribution line dates back more than a century. Johnson says that after languishing for years, the geothermal service is drawing renewed interest, in part because it's up to 30 percent cheaper. "Primarily it's because the price of natural gas has risen so much in the last three to four years," he observes, "but I also think there's more interest in renewable energy, too."

The government-funded report from MIT concluded that non-polluting geothermal plants should become a bigger part of America's energy portfolio. At present, there are just a few other American cities with geothermal utilities. Reno, Nevada, is one. Susanville, California, is another. Klamath Falls, Oregon, installed geothermal heating coils under downtown sidewalks to melt snow and ice.

A member of the expert panel that wrote the MIT report, geothermal consultant Susan Petty, says cities now using geothermal provide just a taste of what's possible. She admits that it's a viable alternative only where the heat source is very shallow. She gestures toward the color-coded maps that cover the walls of her Seattle office. They show where hot rocks lie close to the surface. But, she adds, "there are some easy-to-do incremental improvements to current technology that could bring an awful lot of this energy into being economic."

The MIT panel backs a new approach to mining heat from the earth that can work pretty much anywhere by injecting surface water deep underground. Then you drill a separate well nearby to recapture that water, which is now boiling hot. Petty says the resulting steam can spin a power turbine before being re-injected to start the cycle over again. "We'll be able to manage this flow so we don't lose this water," she explains. "And that was a really big breakthrough because a lot of the high temperature bodies of rock in the U.S. are in the western U.S., where it's sometimes very arid and there's not a lot of water available."

There are two basic categories of geothermal power. There's drilling really deep for super-heated water to use to make electricity. That's Petty's interest. Then there's direct use of moderately hot water that might lie beneath a city or a business property. That's actually more widely accessible.

The Flora Company of Boise uses the hot water under its land to heat its greenhouse and fishponds. The owners drilled a 200-meter well to tap a geothermal aquifer. Head grower Jayson Grazel shows off trays of bedding plants in the toasty warm greenhouse complex. "We have a leg up," he says. "It really saves on the bottom dollar versus paying for gas or extra heat from various ways." He estimates that using geothermal energy cuts the company's heating bill by 75 percent.

The warm water circulates under the floor of the greenhouses or runs through growing tables. It keeps the geraniums, pansies and poppies happy. And the grower, too. "The beauty of it is that it goes back to the earth. It comes out [of the greenhouse] the same way it goes in, just a few degrees cooler."

The recent MIT study on geothermal potential proposed a public investment of $800 million over the next 15 years to jump-start this energy sector. But President Bush's proposed 2008 federal budget does not include money for the suggested geothermal surveying and test drilling or technology prototypes. Other countries are taking the lead on mining deep geothermal deposits. France is taking advantage of European Union subsidies. In Australia, private investors are shouldering the risk.