Impax Environmental Markets

The potential of geothermal power is vast. Tapping the heat from the earth’s core could turn out to be one of the most abundant sources of low carbon, zero-emission renewable energy we have available. The geothermal potential of places like Iceland, Hawaii and New Zealand are well-known, but new technologies now being developed will make it possible to generate heat and electricity from just about anywhere.

The advantages of geothermal power are enormous. Geothermal plants run continuously, and are therefore ideal for providing baseload utility generation. Since most of the activity takes place underground, they take up hardly any land. And since new generation plants are emission- and pollution-free, they can be sited anywhere – even within cities. The technology is well known, and electricity generating costs are low.

The sustainability of geothermal has been demonstrated by power plants running since 1913 in Lardarello, Italy, since 1958 at Wairakei, New Zealand and since 1960 at The Geysers, California. Traditional geothermal plants such as these rely on either ‘dry steam’ technology (where active steam vents are run through a turbine) or ‘flash steam’ (where hot water from a vent is vaporised to produce steam to run the turbine). These are the easy pickings of geothermal power, but very limited geographically.

New technologies are set to change that. The first is the Binary Cycle system, which uses water at much lower temperatures than a flash steam plant: the water is passed through a heat exchanger that transfers the heat to a working liquid with a much lower boiling point than water – this fluid is then vaporised to run a turbine. These plants are incredibly efficient, and produce no pollutants or emissions. The potential is huge. In the US, for example, geothermal surveys traditionally ignored any reserves which registered at less than 350 degrees C: binary cycle plants, by comparison, can produce electricity from sources that are anywhere between 150 and 300 degrees.

The second major technology on the horizon is the Enhanced Geothermal System (EGS). This works by pumping water down into hot, dry rocks and capturing the resulting steam on the way back up. There are technical hurdles to overcome (such as how to fracture the rock between the wells) but EGS offer the potential to vastly expand the power available from geothermal resources anywhere in the world. A report from MIT estimates that over 100 million quads of energy could be harvested globally using this system – and at present the world uses just 400 quads annually.

Finally, geothermal is the power behind domestic ground-source Heat Pumps, which take advantage of the constant temperature of the earth and use it for both cooling and heating.