The future for current energy sources
The Future of Geothermal Power
Geothermal technology uses the earth's heat to produce heating or electricity.
This environmentally-friendly but underused energy source could represent an interesting opportunity for the sustainable development of energy.
Underused Potential
High-temperature geothermal resources worldwide (used to produce electricity) are concetrated in a limited number of countries near active volcanic regions around the globe. Most of these are located in Asia and North America. In all, about twenty countries worldwide produce geothermal electricity, with capacity of about 9700 MW. This energy source plays a key role in some countries such as the Philippines, where it accounts for 17% of electricity produced, and Iceland (30%)1. Golbal installed capacity is expected to double to 18,000 MW by 20202.
Installed capacity for heat production (low-energy geothermal power) is estimated at 27,000 MW. In 2005, over 70 countries stated that they used geothermal power to produce heat, including Japan, China, Iceland, the United States and Europe (2500 MW).
However, the planet's geothermal potential remains largely underused, particularly in developing countries. But as is often the case with renewable energy, a lack of capital development is stalling development. Geothermal wells are expensive, and preliminary studies, operation, and monitoring all require skilled, well-trained personnel. Most developing countries remain dependent on external aid.
The availability of geothermal energy is also geographically limited. Transporting heat over long distances incurs significant heat loss- reconciling production sites with faraway conumption sites is a challenge when meeting energy needs.
Improving Techniques
Technically speaking, natural underground hot water tables are not the only places of interest. In the last few years, geothermal technology has been developed whereby power can be ‘created' by injecting water into ‘dry' rocks, such as fractured or deformed granite. For this, rocks located at great depths are chosen in areas with a high geothermal gradient and high temperatures. The idea is to drill two wells a few hundred meters away from each other. High-pressure water is injected into one of the wells, extending or creating a network of fractures in the rock. The water heated from its passage through the high temperature rocks is pumped into the second well. Once the fractured network is suitable for water circulation, a constant stream of cold water is injected into the rocks and hot water is recovered.
This method has been tested since 2002 in Soultz-sous-Forêt in the Alsace region in Eastern France. Here wells have been drilled 5000m inside a granite massif. In 1997, after ten years of testing and surveys, water circulation was achieved for 4 months between the two deep wells, at a flow of 25 kg/s and a temperature above 140°C, without any water loss or corrosion and at low pump power. This worldwide first paved the way for the project's continuation. A scientific pilot plant is underway involving the construction of three 5000m deep wells. In 2008, a power plant with capacity of 1.5 MW was commissioned. This will provide enough energy to supply a small town.3
• Internal heat sources within the earth's crust (mostly radioactivity);
• Energy input from outside the reservoir (solar heat);
• Underground water circulation that reheats them through contact with heat sources located far from the reservoir before returning to the reservoir.
To use a reservoir in a sustainable manner, these heat resources must therefore be replenished. This may involve:
• Capping the amount of heat used
[1] http://www.edf.com
[2] http://www.geothermie-perspectives.fr
