Energy question of the week: How much energy is there in the Earth's interior?
Ninety-nine percent of the Earth is hotter than 1000 degrees Celsius. Inside Earth's core, temperatures rise to 7000 degrees. In total, the power within our planet amounts to thousands of billions of watts. This reservoir has its origins in the residual heat dating from the time the Earth was created, roughly 4.6 billion years ago, and in the ongoing radioactive decay of long-lived isotopes of uranium, thorium and potassium. The question we need to ask ourselves is why, given these gigantic amounts of energy, does geothermal power still only account for far less than one percent of our energy usage?
Iceland: an island with built-in heating
In principle, electricity and heat can be sourced economically and in a climate-neutral manner from geothermal power plants. But this valuable energy lies hidden beneath our feet and is difficult to access. On average, temperatures only rise moderately as depth increases - by roughly three degrees per 100 metres. However, at a few places on Earth, due to location-specific geological attributes, more of Earth's heat reaches the surface. Volcanically-active Iceland is the classic case in point. This Atlantic island has enough heated and evaporated water just below its surface to supply more than half of the power it needs, driving the turbines in geothermal power stations via heat exchangers. In addition, roughly 90 percent of Icelandic households are heated remotely from geothermal sources.
The Nesjavellir geothermal power station in Þingvellir, Iceland, photo: Gretar Ívarsson - Edited by Fir0002. Top image: Flickr.
In Germany too, geothermal energy can be utilised efficiently, usually not for power generation but for heating. More than 150,000 heat-pump based heating systems are supplied with geothermal energy sourced from shallow depths. The installed thermal capacity of large-scale facilities serving the urban agglomeration in the Upper Rhine Valley approaches 175 megawatts. In order to generate electricity, power stations require temperatures well above 100 degrees Celsius to provide steam to drive turbines. Important experience with geothermal power stations of this kind could be gained in the European research project at Soultz-sous-Forêts. In this test facility in Alsace, the 'hot dry rock process' pumps water to a depth of 5000 metres where it turns into steam at about 200 degrees Celsius and is then used to drive generating machinery.
The geothermal power station in Neustadt-Glewe is an important pilot project in northern Germany that has been supplying ten megawatts of heat and 250 kilowatts of electricity since 2004, using water from a depth of 2250 metres and at a temperature of well over 100 degrees. In the South, the geothermal power station in Landau, with a power generating capacity of three megawatts, stands out. It obtains water at a temperature of 159 degrees Celsius from a borehole 3000 metres deep. Despite these very promising projects, it will take a very long time before more widespread usage is made of geothermal power for electricity generation.
Local residents sceptical after earthquake
The operators of geothermal power stations not only have to contend with the expense of drilling and maintaining deep bore holes and the associated challenges for the materials, they also have to struggle with an acceptance problem. As the earthquake measuring 3.4 on the Richter scale that struck the Basel region in 2006 clearly demonstrated, geothermal power stations are not without some element of risk. The cause of the quake has been identified as water being drawn up at high pressure from a depth of 5000 metres as part of the Deep Heat Mining Project. Although the risk of earthquakes is substantially lower in other regions suitable for the exploitation of geothermal power, local residents remain sceptical about the notion of geothermal projects perhaps constituting the power source of the future. This lost confidence could be won back by adopting a policy of complete transparency about these technologies, coupled with a comprehensive series of risk evaluations. After all, the potential for geothermal power to deliver a sustainable source of energy is too compelling for it to not be included in the energy mix of the future.
European Deep Geothermal Energy Programme
Background information: Geothermieprojekte in Deutschland (PDF, german)
The DLR Energy question of the week in 'The future of energy' Year of Science
The Federal Ministry of Education and Research (BMBF) has given the Year of Science 2010 the motto 'The future of energy'. For this reason the science journalist Jan Oliver Löfken will this year answer a question on the subject of energy in his blog each week. Do you have a question about how our energy supply might look in the future? Or do you want to know, for example, how a wave power plant works and how it can efficiently generate electricity? Then send us your question by email. Science journalist Jan Oliver Löfken will investigate the answers and publish them each week in this blog.