Lately, we've heard a lot about alternative sources of energy, like geothermal energy, for instance.

The simplest understanding of geothermal technology, is that it employs hot rocks to create energy. Granite deep in the earth holds heat that with a little ingenuity can be harvested for electricity.

The process engineers call enhanced geothermal involves drilling several holes two to three miles into the earth. The granite contains a broad network of cracks that can be widened with pressurized water. Water is pumped into a hole, and its temperature rises to superheated conditions as it travels through this system of cracks. When it exits through another hole, the drop in pressure causes the water to boil and release steam that creates electricity via a steam turbine. Exactly the same pressure drop process causes Old Faithful to blow off so regularly.

Best of all, it doesn't emit any pollutants.

The problem is, that the cost of drilling won't be cheap, and there are concerns as to whether the relatively low-temperature heat is worth those costs. At the same time, this isn't a new phenomenon. Geothermal energy is already being successfully exploited in other areas of the world. An Energy Department study suggests geothermal energy has the potential to produce 10% of the electricity in the United States by 2050.