Commissioned by Geothermie Unterhaching GmbH und Co. KG, the plant is designed to generate 3.36 megawatts of power and will work according to the Kalina system.

This involves using a mixture of water and ammonia as the working medium, which boils over in a larger temperature range at a defined pressure than water or pentane.

This will enable heat from low-temperature springs to be converted into electrical energy more efficiently than conventional installations, according to Siemens.

"The heat efficiency of the Kalina principle is therefore considerably higher than a water-steam circuit or organic Rankine circuit (ORC) and, even at low temperatures, will enable economically efficient operation of the plant," Siemens said.

Siemens will supply and install all of the above ground parts of the power station installation. This includes the heat-exchanger circuit, the steam turbine with generator, and the cooling circuit, as well as all the automation and control systems, based on Simatic PCS7.

In addition, Siemens is supplying all the power systems and equipment, including medium and low-voltage transformers, a 22 kilovolt, a 6 kilovolt and a low-voltage switchgear installation, as well as the power distribution, direct current supply and grounding equipment.

Siemens is also responsible for construction of the administration building, including the control centre, the machine building and the cooling tower basin.

Siemens will also provide 10 years of maintenance to the plant, which is expected to start commercial operation mid-2007.

Located in the south-German Molasse basin, the Unterhachin-based project involves porous limestone containing water at temperatures over 100 °C at about 3000-metre depth, Siemens said.

The local community, of 21,000 people, set up Geothermie Unterhaching GmbH und Co. KG to exploit this source of hot thermal-spring water.

"We urgently need more power and heat from low-temperature springs," Unterhaching mayor Dr. Erwin Knapek said.

"We are therefore now building the most modern plant of its kind in Unterhaching.

"Siemens was awarded the contract for this geothermal power station because the competence of the company was the best way of ensuring that the local citizens will benefit from a sustainable supply of electricity and heat."

In 2004, exploration drilling encountered 122°C water at a depth of 3300 metres. The well is expected to produce hot water at 150 litres per second.

From this, 25 litres per second will be used to generate heat for the district heating system, while the remaining 125 litres per second will be used to generate 3.36 megawatts of electrical energy in the new geothermal power station.