Geothermal Energy

HOT AIR OR STEAMY SOLUTION? GEOTHERMAL ENERGY

With all the talk of solar and wind energy, we sometimes tend to overlook other potential sources that are renewable and sustainable alternatives to the fossil fuels we’ve come to depend upon for over one hundred years. The question with all of them is: what is their output potential and just how ‘green’ are these energy sources really?

WORDS MICHEL CRUZ

As a sustainable energy source, geothermal has the capacity to produce heating and generate electricity from the heat – or thermal energy – stored under the earth’s surface. Temperatures in the huge inner core of our planet are incredibly high, partly due to pressure, to energy stored under the crust from the formation of the earth, and from the decay of radioactive material associated with this. In all, the earth’s subterranean heat content is about double the present energy requirement of all humans living on the surface, but it isn’t as easy as all that, as the process to harnass it is only viable in locations where the hot steam can be tapped at the surface or drilled down into.

Taken together, geothermal energy nonetheless forms a potentially huge source for heating and the production of electricity, but the extraction and production processes come with their own challenges and limitations. Nature gave us the example of potential heat extraction early on, as there are many spots around the world where natural geysers spray geothermally heated water jets high into the air. Think of New Zealand, Iceland and of course ‘Old Faithful’ at the Yellowstone National Park in Wyoming, USA. ›

The earth’s inner heat bubbling up to the surface

Old Faithful, the famous geyser at Yellowstone National Park

The world’s most famous geyser – a huge tourist attraction in its own right – is so called because it erupts like clockwork every 90 minutes, but in spite of this natural source of inspiration it wasn’t in the USA that the use of the earth’s thermal energy for heat and electricity production was first pioneered. No, not even in Iceland, the country that has long been most famous for it, but Italy, where a pioneer called Prince Piero Ginori Conti initially experimented with the concept and built the world’s first experimental geothermal power station over a century ago.

GEOTHERMAL POWER

The first commercial power station of this kind was built in New Zealand in 1958, followed by more in Iceland, the USA, Japan, France and Germany. Right now, 26 countries around the world are making use of the ‘free’ provision of geothermal energy to produce electricity, while the resource is used for heating in 70 nations and the number and scope of both kinds of projects is growing apace. World output stands at around 17.5 gigawatts (GW), which though considerable is just a fraction of the energy required and produced every year, and also roughly onetwentieth of the potential capacity of geothermal energy.

Developing all the potential that lies under the earth’s crust will, however, require a great deal of further investment, technological development and the perfecting of extraction and storage systems around the world. Part of this will involve the improvement of drilling techniques, which will open up a great deal more of what lies below. Naturally, the best access points are not evenly spread across the world, and some countries have greater geothermal resources than others, with Indonesia thought to have the greatest amount of all, followed by the likes of the USA, Canada, New Zealand, Iceland and Russia.

SYSTEMS USED

Over time, different systems have been developed to extract thermal heat and convert it into electricity, and currently there are three in use. The first of these is Flash Steam Technology, as used in the commercial power station inaugurated in 1958 at Wairakei in New Zealand. In essence, geothermal power stations are not that different to others in that they use heat from a natural source on the earth’s surface to heat water (for instance) and produce electricity by moving the turbine of a generator. The water is afterwards cooled and returned to the earth. ›

Countries such as Iceland supply a large part of their electricity needs through geothermal plants

Geysers have curative powers but are also potential sources of energy

FLASH STEAM

This system uses high-pressure hot water from deep in the earth and feeds it into low-pressure tanks, powering the turbines from the resulting flashed steam. The commonly used system requires water temperatures of 180°C and qualifies as a renewable and therefore sustainable energy source.

DRY STEAM

The oldest and most straightforward of the three techniques developed so far, it isn’t so common because it requires the rarer occurrence of dry steam. It works by extracting hot steam from hot water in natural reservoirs and requires a minimum temperature of 150°C. After use, the steam passes through a condenser and is returned to a liquid state and to its original source, so this too is a fullcycle process.

BINARY CYCLE

First developed in the Soviet Union and later also introduced to the West, Binary Cycle geothermal power production is the most recent process developed, and it has the advantage of being able to use water at much lower temperatures, starting at 57°C – which opens up far greater potential for production around the world.

The process works by passing moderately hot water through a second liquid with a much lower boiling point, which produces a flash steam effect that drives the turbines. Here too, all liquids involved are safely returned to their original sources, and the system ranks as sustainable, though conventional energy is of course required to work the machinery, but it is 20 times less than that demanded by a conventional power station.

FUTURE POTENTIAL

The environmental impact of this renewable energy source is therefore minimal, but detailed geological studies of potential sites is important, as it has caused subsidence and even earthquakes, the latter due to the extraction and re-injection of large amount of water and steam. In fact, some locations have had to be abandoned due to the (potential) danger, so as more and more fields are developed in the near future, careful attention will have to be paid to their suitability, or else we merely transfer environmental damage from one source to another.

If done properly, geothermal can become an important contributor to the shift to renewable energy sources, as even at full viable production, it will extract only a relatively small amount of the earth’s thermal heat capacity. If development and investment continue to accelerate, it can account for 3-5% of our energy needs by 2050, and reach approximate full potential at 10% by 2100.

Geothermal will never be the magical one-stop solution to humanity’s power requirements, but it is renewable, sustainable, generally safe and a big potential source in localised settings around the world, so yes, this is a steamy option worthy of excitement. e

Steam forms a vital part of the process