The U.S. geothermal energy industry ended 2012 with a growth of 5 percent, which is modest but nevertheless a good progress for an industry that feels a bit left out of the renewable energy boom.

The country added 147.05 megawatts of new generation capacity last year, bringing the total capacity to date to about 3.39 gigawatts, according to the Geothermal Energy Association, which issued its annual report Tuesday.          

"The industry has continued to grow, and policy and technology are there to help moving things forward," said Karl Gawell, executive director of the association, during a press conference call Tuesday.

The new capacity may seem paltry compared with the 13.1 gigawatts of wind installed or the roughly 7 gigawatts of solar in 2012, but geothermal power development is a whole different beast all together. Developers could spend years and millions of dollars to drill wells just to see if they hit a reservoir of steam big enough to be worth more investment and time. After that, they still need to drill production wells, build the power plant and raise the money to complete the project.

In California, the biggest geothermal energy producing state, developers like to size their projects at 49.9 megawatts, just shy of the 50-megawatt limit over which they would need to secure a permit from the California Energy Commission. Still, a 49.9-megawatt geothermal power plant can take a lot longer to build than a same-size project using solar panels. Developers could cut short the time by building another 49.9-megawatt project next to an existing geothermal power plant provided, of course, that the reseource reservoir is sizable enough to support the two.

Unlike wind and solar, geothermal power plants can produce electricity around the clock. That ability would seem to make geothermal energy a more desirable replacement for dirtier power plants that run on coal and natural gas. But geothermal industry leaders have expressed what they see as unfair regulations that favor solar and wind instead.

Geothermal power plants are mostly limited to more remote regions — you can't plop one down in urban areas or on a suburban rooftop like you could with solar panels. California also allows utilities to pay a premium for solar when they sign power purchase agreements with developers, a policy that makes geothermal power proponents grumble.

On the federal level, you have the the Sunshot Initiative from the Department of Energy that dolls out grants to companies that work on reducing the costs of manufacturing, installing and even marketing solar energy (to consumers). Its effort for geothermal energy development is more limited, not the least because you don't see as many startups entering the field with new innovations.

There is one startup that has gotten a good share of spotlight in recent years. Alta Rock Energy has generated buzz because it counts Google, Cleaner Perkins and Kholo Ventures as among its investors. Alta Rock is trying to commercialize a process to create steam reservoirs in places that have hot rocks but no water. Called "engineered geothermal system," or EGS, the technology could place geothermal power plants in many places beyond the western U.S., where most of them are located today.

But getting that technology right is tricky. The company has been working on a demonstration project in Oregon for a few years and recently reported that it was able to control the creation of steam in different areas of the project site. To bring the technology to market may well take a few years more at least.

You will find geothermal power plants in eight states today: Alaska, California, Hawaii, Idaho, Nevada, Oregon, Utah and Wyoming. Some of the projects under development are proposed in other states, including Colorado and Texas. Overall, 185 projects of over 5 gigawatts are currently under development, the industry association said. Roughly 2.5 or 2.6 gigawatts will likely be built over the next decade.

Lead image: Geothermal plant via Shutterstock