Radiation selective absorber coating for an absorber pipe, absorber pipe with said coating, and method of making same

An absorber pipe (13), especially for a parabolic trough collector, said absorber pipe (13) comprises a steel pipe (1) with an outer surface and a radiation selective absorber coating on said outer surface of said steel pipe (1);

• wherein said radiation selective absorber coating comprises at least two barrier layers (24a, 24b) arranged over each other on said outer surface of said steel pipe (1), an infrared-range reflective layer (21) arranged on said at least two barrier layers (24a, 24b), an absorption layer (22) arranged over said infrared-range reflective layer (21) and an antireflection layer (23) arranged over said absorption layer (22);
• and
• wherein said at least two barrier layers comprise a first barrier layer (24a) and a second barrier layer (24b), said first barrier layer (24a) comprises a thermally produced oxide layer and said second barrier layer (24b) comprises an AlxOy layer, wherein x=1 or 2 and y=1, 2, or 3.

A method of operating a parabolic trough collector, said parabolic trough collector comprising an absorber pipe (13) through which a heat-carrying medium is conducted, wherein said absorber pipe has a radiation selective absorber coating (20) on an outer side thereof and said radiation selective absorber coating (20) comprises at least two barrier layers (24a, 24b) arranged over each other on said outer side, an infrared-range reflective layer (21) arranged on said at least two barrier layers (24a, 24b), an absorption layer (22) arranged over said infrared-range reflective layer (21) and an antireflection layer (23) arranged over said absorption layer (22);

• and wherein said at least two barrier layers comprise a first barrier layer (24a) and a second barrier layer (24b), said first barrier layer (24a) comprises a thermally produced oxide layer, and said second barrier layer (24b) comprises an AlxOy layer, wherein x=1 or 2 and y=1, 2, or 3;
• and said wherein said method comprises conducting a heat-carrying liquid with a boiling point less than 110° C. through the absorber pipe (13).