In the shadows of wind and solar, another clean energy source is rapidly gaining steam and inciting equally lucrative profits.

With about 10,500 MW installed to date, geothermal energy hasn't yet reached the scale of its cleantech cousins. Wind, for example, has ~142,000 MW of installed capacity worldwide; Solar has about 18,000 MW.

But the wonders of geothermal energy are spreading far and wide. Its capacity is forecast to double in the next five years to ~21,000 MW.

And related stocks have been offering hefty returns to those willing to take a look at this unloved sector. Let's take a closer look to see if we can claim some of those profits for ourselves.

Investing in Geothermal Energy

Here's a chart that shows how geothermal has grown since the turn of the century. . . and how it's forecast to grow over the next decade:

We're dealing with an industry that is about to witness solid growth, spurred not only by energy and climate concerns, but also by policy and financial incentives.

Everyone from Google to Middle Eastern oil sheiks are already lining up to get a piece of the imminent action. Google has invested millions in enhanced geothermal systems. And Masdar, the entire cleantech city being built in Abu Dhabi, awarded multi-million dollar contracts this week to begin drilling geothermal wells.

This is partly because of the nature of geothermal energy. Unlike solar and wind, geothermal is capable of providing steady base load power with some of the highest capacity factors around.

But it's also because of its profit potential. Look at how stalwart geothermal company Ormat Technologies (NYSE: ORA) has blown away the Dow Jones over the past six months:

Some of that growth has come from increased activity in the United States, which boasts the largest geothermal market in the world with about 3,000 installed megawatts of capacity.

Ormat has been busy assisting and providing geothermal systems to a few smaller companies here in the states, as stimulus dollars thrust projects forward.