Exhibition keeps nuclear debate tropical

Iron brew: the earth was originally a glowing, molten ball Tropenhaus Frutigen

Why is the earth hot and where does natural radiation come from? An exhibition on geothermal energy at the Tropic House at Frutigen explains all.

This content was published on March 30, 2011 minutes

The centre in canton Bern looks at the phenomenon of natural radioactivity, takes visitors back to the Big Bang – and lets them taste locally grown bananas.

You might have learnt at school that the history of the Earth began with the Big Bang more than 13 billion years ago. You might also know that it was originally a glowing, molten ball that slowly started to cool – and the hardened crust on the surface became the ground beneath our feet.

But the exhibition, which runs until the end of October, digs beneath the surface and explains how the deeper we go, the hotter it gets, and were we to go down 6,370 kilometres, the temperature would be a hellish 6,900 degrees Celsius.

Radioactivity generated by the forming of the universe is also present – a sort of residual heat – the result of the decay of natural radioactive elements.

“It’s incredible to think that below us is enough liquid heat to provide us with energy for the next million years,” Samuel Moser, head of research and development, told


That the exhibition is taking place in Frutigen is not a coincidence: the hot interior of the earth and the Tropic House are closely linked, for without the warm mountain water from the Lötschberg base tunnel, which opened in 2007, the project wouldn’t exist.

The Tropic House uses warm water, a by-product from the construction of the tunnel, for the greenhouses where bananas, papaya and pineapples are grown. Perch and Siberian sturgeon are also farmed.

Every second, 100 litres of 20-degree water (hot bathwater is around 40 degrees) flows from the north entrance of the tunnel. This can’t run into local bodies of water without harming the reproduction of lake trout.

“The warm mountain water was always a cornerstone of the entire exhibition, but the water itself was never really discussed,” Moser said. “We were always asked by the public why the water is warm and how it gathers in the mountain – so we put in the exhibition.”

Going underground

Frutigen is considered a pioneer when it comes to renewable energy. However, the Bernese Oberland is not an ideal location for a geothermal power plant, even if engineers bored 2,000 metres underground to build the Lötschberg Tunnel, reaching depths that are “geothermally significant”, as Moser put it.

When you build a tunnel, you bore horizontally; to extract heat, however, you have to go down vertically, which is expensive and would have been too complicated given the tunnel’s safety regulations.

“The important thing with geothermal power plants is to be near built-up areas, which need the heat from the earth,” Moser said.

“It’s pointless building something out in the sticks that might generate loads of heat but which then has to be transported for kilometres through expensive pipes. So one looks for places such as St Gallen and Basel.”

Ohm sweet ohm

Geology is a complex subject and most people don’t know much beyond volcanoes and earthquakes.

Nevertheless, the exhibition succeeds in clearly breaking down information and making it intelligible via tables, graphics, exhibits and models.

One of these portrays the earth as an apple – we’re told that the deepest ever drilling into the earth’s crust (12.2km) would be the equivalent of a slight scratch on the apple’s skin.

Of particular interest – especially to younger visitors – is the Geiger counter, which measures natural radioactivity in rocks.

“They can experience first-hand how this ferrous rock from canton Valais emits a high radiation of alpha, beta and gamma rays – how it’s radioactive,” Moser said.

“Valuable contribution”

Natural radioactivity is a big topic at the exhibition, which is sponsored by Bernese power provider BKW, the operators of the Mühleberg nuclear power plant and Nagra, the national organisation charged with the disposal of radioactive waste.

It raises the question of whether the exhibition is connected to the current debate about nuclear energy and the national vote on building new power stations in the coming years.

For Moser, it’s about objectifying the debate. “People generally equate radioactivity with nuclear power stations, which already have a negative connotation.”

He believes showing radioactivity as a natural phenomenon is a valuable contribution.

“Nuclear power stations simply concentrate this natural decay and make use of the resultant energy,” he said.

Geothermal heating

Switzerland has some 50,000 small geothermal facilities providing heat and energy to houses, apartments, offices and hotels – the highest density of geothermal installations in the world.

In 2008 total heat consumption in Switzerland was 110,000 GWh, of which 12.4 % came from renewable sources (wood, rubbish, solar, geothermal).

Geothermal sources provided 1.9% of the total; borehole heat exchangers were responsible for 1.4%.

Borehole heat exchangers use warmth at depths of up to 400m.

Other ways of using underground warmth include the installation of heat exchangers in the piles of foundations.

At a depth of 15-20m, the temperature is about 9-11 degrees; at 120-150m it is 12-15 degrees.

Switzerland has more than 700 road and rail tunnels. A by-product is hot water from inside the mountain which can be used for heating.

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Geothermal energy

Geothermal energy is a “natural” form of nuclear energy: the result of the radioactive decay of elements present in nature, such as uranium.

In favourable geological conditions it can be used for power generation.

Prince Piero Ginori Conti tested the first geothermal generator on July 4, 1904, at the Lardello dry steam field in Italy.

The largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California, United States.

As of 2008, geothermal power supplied less than 1% of the world's energy.

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