Spherical plain bearings ensure efficient operation of 50MW solar power plant

Paul Boughton
More than one thousand high precision plain bearing rod ends from the Schaeffler Group are enabling the efficient operation of the Andasol solar power plants in southern Spain, currently the largest parabolic trough solar power station in the world.

The Andasol 1 solar power plant, which went on line in mid-2009, uses a total of 1,248 ELGES hydraulic rod ends from Schaeffler. The function of the bearings is to support several hundred hydraulically adjustable, parabolic troughs, positioning them with millimetre precision and ensuring that the troughs continuously follow the sun. The rod ends are therefore directly responsible for the plant’s overall efficiency and economic viability.

“High precision bearings are required here so that the power plant can operate at maximum efficiency. Moreover, the bearings also have to withstand loads that should not be underestimated,” said Dr. Arndt Schweigert, Head of Power Generation Sector Management at the Schaeffler Group.

Schaeffler’s Power Generation Sector has developed special bearing solutions for renewable energy projects, including solar and hydroelectric power plants. In these types of projects, plain bearings are optimised for the slow, precise swivel motion. It is critical that these movements are smooth, without any stick-slip or jolting on start-up.

At the same time, the hydraulic rod ends can support high forces and are suitable for alternating loads. This means that the 150m-long collector chains can be adjusted precisely to within a tenth of a millimetre, enabling the troughs to follow the sun on its daily path from east to west.

The hydraulic rod ends are fitted with manganese phosphate-coated radial spherical plain bearings with steel/steel sliding contact surfaces. This special surface treatment improves the running-in characteristics and reduces friction. The inner ring of the spherical plain bearing has a width of 70mm, a cylindrical bore diameter of 110mm, as well as a spherical outer slideway. The 160mm diameter outer ring has a cylindrical outer surface and a concave inner slideway with a diameter of 140mm.

 
Schaeffler also provided 7,488 environmentally-friendly (lead-free) plain bearing strips for the Andasol 1 plant. These strips are mounted in the supports between the individual segments of the 150m collector chains, ensuring smooth slewing movements during the tracking of the sun.

 Developed by Solar Millennium AG based in Germany, the Andasol power plants are located in Andalusia, southern Spain. Each of the three solar power stations are identical in terms of their construction and size and will be the first solar-thermal power stations to be constructed in Europe.

The 50MW Andasol 1 plant went on line in mid-2009 and now supports the power demands of more than 200,000 people, saving around 150,000 tonnes of carbon dioxide. Andasol 2 is currently in the testing stage, while Andasol 3 is still under construction.

The power plants comprise three main parts, the largest of these being the solar field, which has a collector area of more than 510,000 square metres – equivalent to around 70 soccer pitches. There is also a conventional power plant area and a heat accumulator, which ensures that that the three plants are able to supply electric power even after sunset or when there are cloudy weather conditions.

The main element of a parabolic trough solar power plant is the solar field, which provides steam for the conventional steam turbines. The field consists of numerous parallel rows of solar collectors or panels, which are arranged on a north-south axis and follow the path of the sun from east to west. To enable the solar panels (mirrors) to track the sun, each collector unit is fitted with its own solar sensor and hydraulic drive.

The trough shaped parabolic mirrors collect the solar radiation and focus it onto an absorber pipe, which is positioned in the focal line of the collector. This closed circuit pipe system contains synthetic oil, which acts as a heat transfer medium. The oil provides high stability in temperatures up to 400 deg C. The heated oil is then pumped to a power block where it flows through a heat exchanger. The next stage is similar to the steam cycle used in conventional power plants, whereby the steam generated in the heat exchanger is used to drive a turbine connected to a generator. The steam in the turbine condenses back into water, which is then recirculated.

In addition to developing bearing solutions for solar and hydroelectric power plants, Schaeffler is also working closely with developers of the latest wind, tidal and wave energy systems. The Power Generation Sector at Schaeffler also develops bearing solutions for dams, wind turbine gearboxes, conventional energy generation and power transmission systems.

“We consider regenerative energy as a strategic growth sector and we will systematically expand this side of our business,” commented Robert Schullan, President of Schaeffler Group Industrial. “Solutions from Schaeffler are already making a vital contribution to the economic efficiency and reliability of these new technologies.”

For more information, visit www.schaeffler.co.uk

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