Protecting the environment together

Environment News

Geothermal Energy

We are sitting on top of an almost limitless stock of energy!

All we have to do is find a way to use it?

An adaptable energy with high performance

Geothermal Energy is heat (thermal) derived from the earth (geo). It is the thermal energy contained in the rock and fluid (that fills the fractures and pores within the rock) in the earth's crust. These heat resources can be classified as low temperature (less than 90°C), moderate temperature (90°C - 150°C), and high temperature (greater than 150°C). The uses to which these resources are applied are also influenced by temperature. The highest temperature resources are generally used only for electric power generation. Uses for low and moderate temperature resources can be divided into two categories: direct use and ground-source heat pumps.

The purpose of a geothermal facility is to extract the energy stored in the heart of the earth and use it for heating or to produce electricity from the steam generated. However, this heat can only be extracted if underground geological formations are permeable or cracked, so that hot water can rise to the surface. In some cases, rock discontinuities enable hot water to surge through cracks at tens of thousands of litres per hour in a thermal spring. There are many sites of this type in France, particularly in Chaudes-Aiges, Southern Auvergne (in the Cantal Department), where water surges out at 82°C. It is the hottest spring in Europe.

Clearly, the difficulties in harnessing geothermal heat vary depending on the geological context and depth. Some regions are more favourable than others and there are deposits of geothermal energy in the same way as there are oil deposits. Hot water can be found almost everywhere, provided that we drill far enough, but it is obviously better to search for the best sites, where hot water is close to the surface. Steam or this water can then be used in geothermal power stations to generate electricity or supply a heating network for buildings.

Geothermy is used in France for heating and cooling and there are many pilot projects. France is considered a pioneer in Europe. The only European country that makes greater use of geothermal energy is Iceland, where the capital, Reykjavik, is 82% heated by geothermal. The contribution of geothermy to French energy production is far greater than solar and wind generated energy. It is estimated that there are 6 MTOE (Million Tonnes of Oil Equivalent) per year of usable geothermal reserves in France.

Globally, geothermal heat has been used mainly in locations where hot water was found, which is a severe limitation. To develop geothermal energy for the future, ways are needed to increase the number of attractive areas, for example the ‘hot dry rocks’ technique, as used in the Soultz-sous-Forêts project in the Alsace region of France (www.soultz.net), which uses heat from rocks without the presence of hot water. This method consists of fracturing rocks between two boreholes and pumping in cold water from the surface, to heat it as it comes into contact with deep rocks. In France, sites with a calorific potential of more than 180°C at a depth of 5,000m have been identified in the Languedoc-Roussillon region and in the Massif Central. According to expert estimates, the Earth’s temperature at a depth of 40km is 1,000°C. Therefore we live on an almost limitless stock of energy. All we need to do is to discover how to harness it.

Another expanding application is called ’surface geothermy’ and uses heat pumps. This makes use of the least visible fraction of geothermal energy and can be used to heat or air condition small buildings. Using resource temperatures of 4°C to 38°C, the heat pump, a device that moves heat from one place to another, transfers heat from the soil to the house in winter and from the house to the soil in summer. These heat pumps open up new possibilities and are feasible almost anywhere. The technique consists of drilling a pair of wells to a depth of about 150m, so that a heat exchanger composed of polyethylene tubes can be inserted. The fluid that circulates in these tubes collects heat from the rock to supply a heat pump on the surface.

Direct use, as the name implies, involves using the heat in the water directly (without a heat pump or power plant), for such things as heating of buildings, industrial processes, greenhouses, aquaculture (growing of fish) and resorts. Direct use projects generally use resource temperatures between 38°C to 149°C.

The current production of geothermal energy places it third among renewable energy sources:

1. hydroelectricity

2. biomass

3. geothermal

4. solar and wind

Only a minuscule portion of the world’s geothermal energy has been explored. The current level of use pales in comparison to the potential. The key to wider geothermal use is greater public awareness and technical support.

ADVANTAGES of Geothermal Energy

• It is a reliable energy and stable with time, since it does not depend on atmospheric or climatic conditions. It is available all day, all year round and in many areas of the world.

• It respects the environment and has little or no effect on it. It generates almost no polluting substances, very little carbon dioxide and only a small quantity of hydrogen sulphide. Most of these products are re-injected into the groundwater and not into the environment.

• Geothermal wells have a very limited visual impact. Once a well has been drilled, it is completely invisible, since the wellhead is buried.

• Using geothermal electricity, hydrogen may also be produced as a secondary energy carrier for automotive propulsion or use in fuel cells.

• An answer to different energy needs: power, heating, cooling, hot water.

• It is economically sustainable, with reduction in energy cost plus is not sensitive to conventional energy prices.

• Reliable and proven technologies already exist, e.g. drilling, heat pumps, etc.

DISADVANTAGES of Geothermal Energy

• Geothermal water is often saline, with a very high content of mineral salts, up to three times more than seawater! It can only be used through a heat exchanger, in other words a device through which it transfers its heat to a parallel heating circuit containing fresh water. The two liquids never come into contact resulting in a loss of efficiency.

• Geothermal water is almost always corrosive. This corrosion (due to salt, but sometimes also bacteria) increases maintenance costs.

• There is a risk of pollution when the extracted water contains heavy metals. This water has to be re-injected into the ground water.

• Although the extracted energy is free, investment and maintenance costs are very high.

• Depletion of the resource is possible. Underground hot water stocks are considered renewable since they are continuously heated by the internal heat in the earth, but the rate of use must not exceed the rate of renewal.

• The use of geothermal energy remains limited to very specific regions, particularly close to volcanic areas.

If we drill far enough, we will find either oil or hot water, but it is not enough to drill a well anywhere and hope to find a layer of hot water. Sedimentary basins are the best areas, but precise prospecting is necessary even within these areas. Considering the high cost of wells, it is important not to get it wrong, or at least to make the fewest possible mistakes. There are two main difficulties in drilling a geothermal well; the first is to find the best site within the chosen area and the second is to prevent corrosion of the tubing.

Power from geothermal energy has been produced commercially for more than a century and the use of geothermal energy for domestic application goes back to well beyond 200 BC. Geothermal energy is reliable and it is clean. It can produce power 24 hours a day, all year long. It can be produced from our own soil. Geothermal energy is generated inside the earth and its exploitation faces the same risks and rules as for any other deep underground mining activity. However, the world still knows very little about most geothermal resources and the technologies required to drill or mine for that heat.

Martin Parr

First European Geothermal Review - Geothermal Energy for Electric Power Production

October 29 – 31, 2007

Favorite Parkhotel, City of Mainz, Rhineland Palatinate, Germany

The purpose of this First European Geothermal Review is to have a critical look at today’s developments in geothermal energy, discuss various controversial exploitation technologies & philosophies, study successful and problematic projects, see where we stand today and try to learn from each other. Specifically, the agenda is to address risks associated with exploration, development, power distribution and maintenance.