Electric current from the depth

"Supercritical water" above 500 C could multiply the current yield

Aerial view of the geothermal power plant at Krafla in the north of Iceland. The first deep hole in the foreground of the picture is to be drilled in supercritical water. Here is a Magmenkammer in only about 4 km depth. © Emil Thor
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Iceland is rich in renewable energy: geothermal power plants not only generate electricity but also hot water for public baths, heaters and private households. Even parking lots and sidewalks in the Icelandic capital Reykjavik are kept free of snow and ice in winter. But that's not all. Now scientists want to use a research well to tap around 500 ° C hot water. This so-called supercritical water could deliver up to 10 times more electricity than conventional geothermal power plants in Iceland.

The country is so rich in underground heat because it lies on the active Mid-Atlantic ridge. This magmatic back pervades the entire Atlantic Ocean like a huge submarine mountain range. Fresh magma constantly pouring out of the earth's mantle shifts the ocean floor apart - every year the Atlantic gets four centimeters wider on average. Only in a few places, the back rises above the water surface and forms an island, such as Iceland. Therefore, temperatures below 250 ° C prevail under two to three kilometers below the island. The abundant rainfall seeps through countless cracks and fissures into deeper rock formations and are heated there - ideal conditions for geothermal use.

With today's standard drilling technology, the repeatedly refilled geothermal reservoirs can be unlocked and recovered. To put it simply, only one generator turbine is connected to the top of the wellhead and driven by the excess pressure steam. Even today, the large geothermal power plants in Iceland supply three energy-hungry aluminum smelting works, making Iceland the world's largest exporter of aluminum - but for a direct export of electricity, the island is too remote from industrial and residential centers.

Supercritical water: neither liquid nor gaseous

The principle section through a deep magma chamber (red) shows how rainwater sinks and is heated up. A hole of about 5 km depth closes this high-energy reservoir (orange boundary) and allows to promote supercritical fluids. IDDP

In the near future, an international consortium of scientists led by the International Continental Research Drill Program ICDP, coordinated at the GeoForschungsZentrum Potsdam, hopes to open up a much richer source on Iceland: supercritical water. The planned deep wells are to be dredged at four to five kilometers on salty waters with temperatures of around 500 C. From a temperature of over 374 C and a pressure of 221 bar (these values ​​are slightly higher with saline deep waters), pure water shows no difference between liquid and gaseous the boiling curve ends at the "critical point". This state of matter is called supercritical. The special feature: Due to the extremely high water vapor yield, supercritical water could generate up to ten times the amount of electricity compared to normal Icelandic geothermal power plants.

The drilling and experiments planned on Iceland are to be used for the first time in nature to test this phenomenon, which was previously known only from large-scale power plant operation. The team of scientists is preparing the first well for the extraction of supercritical water, supported by Icelandic energy companies and authorities. However, technicians and scientists are not only interested in overcoming the "subcritical" area and extracting supercritical water from the depths. Rather, a continuous drill core below three kilometers down to the bottom of the hole is to be explored in order to investigate the interaction processes between hot volcanic rock and water. display

How do mineral deposits form?

Pipelines feed hot steam in Iceland from multiple wells to power plants. Thomas W hrl, GFZ Potsdam

As the temperature increases, the exchange processes between rocks and solutions, which are responsible, for example, for the formation of many mineral deposits, intensify. Supercritical solutions not only transport heat from the rock, but also dissipate large quantities of metals, transport them and, after cooling, deposit them again under certain conditions, now but often in concentrated form. At the same time, the leached rock changes in its mineral content and structures. A significant portion of the gases released in the supercritical waters come directly from the crystallizing magma and provide the scientists with important information on its origin and development.

If the first experiments in 2007 and 2008 are successful, Earth Sciences will have a completely new underground laboratory at its disposal, where water-rock interactions can be directly observed. This could improve the conditions for the use of renewable energy sources in volcanic regions and study the development of ore deposits. The volcanic island of Iceland offers the ideal environment for this.

International cooperation

The planned core drilling will be funded by the ICDP in conjunction with the US National Science Foundation and supported by a number of technical and scientific measures. The ICDP, led by the GeoForschungsZentrum Potsdam, supports international research initiatives that urgently need drilling for their investigations. The main scientific topics of the ICDP-funded process research are, for example, the causes of earthquakes, climatic and environmental changes in the past, meteorite impacts, the development of life but also volcanism and geothermal energy, as in the now planned drilling in Iceland.

Left:

Geothermal Research in the Icelandic Rift Zone (Scientific Drilling No. 4, March 2007, pdf - 6 MB)

Iceland Deep Drilling Project

International Continental Scientific Drilling Program

GeoForschungsZentrum Potsdam

(Ulrich Harms - ICDP, GeoForschungsZentrum Potsdam, 09.03.2007 - AHE)