Absorber tubes for solar thermal energy

Solar thermal power plants

  • The tubes need to withstand contact with hot thermal fluid   
  • High light absorption of the tube    
  • Uniform coating of the entire circumference of the tube

Sputtering coating system for selective absorber coatings on heat transfer tubes


Solar energy is free and it is also very reliable in dry areas. Unlike photovoltaic systems, solar thermal energy does not require technically complex semiconductor components, but rather directed light radiation. In the design relevant here, mirrored parabolic troughs focus sunlight onto an absorber tube. The liquid flowing through the absorber tube is heated up to 450°C in the process. This heat can then be used in any thermal power plant to generate electricity. The absorption rate of the absorber tube is crucial for the efficiency of solar thermal energy collection. For this reason, the entire circumference of the tube is coated with a selective absorber layer – a stack of metal-ceramic layers – which achieves absorption coefficients of more than 90%.

Requirements for the system

The system should be able to coat up to twelve stainless steel absorber tubes all at once. The tubes are 4 m long and the entire circumference needs to be coated evenly with an anti-reflective coating that consists of several individual layers. The system needs to have the high productivity required by a production facility and also relieve the operator of moving heavy loads.

Solutions to requirements

The FHR.Line.1200.V is a vertical in-line system with an entrance load lock, process area and exit load lock as well as a carrier return system. The gigantic carriers (substrate holders) into which the tubes are inserted have a device that allows continuous rotation of all tubes so that they are coated uniformly from all sides. Rotary and planar targets are used in the actual process area. The flanges with the sputtering targets fold open towards the front to make changing the 1200 mm targets easier.

System features include:   

  • Coating on all sides thanks to rotation in vacuum   
  • Substrate: Stainless steel tubes with various diameters  
  • Carrier transport including return system completely developed and automated by FHR    
  • Highest material utilization and longest target service life using rotary cathodes


Deposition of thermal absorber tubes

Vertical inline sputtering system