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Non-toxic Electroplated Coatings for Solar Parabolic Trough Collectors

Despite contributing to 50% of the global energy demand, thermal energy has often been neglected as an application for renewable energy technologies, instead losing ground to electricity production via solar cells or wind turbines. Solar collectors, particularly parabolic trough collectors (PTCs), have the potential to sustainably meet much of this thermal energy need.

A current challenge for solar collectors is the selection of material for the solar selective absorber, also called the receiver. The chosen material must have high absorbance / low emittance of wavelengths in the solar spectrum. Additionally, the material must maintain thermal stability under high temperatures. Some currently used materials, such as hexavalent chromium, are toxic, while others require expensive equipment for fabrication.

 In the search for a cheap and safe PTC receiver material, Zäll et al tested a cobalt – chromium coating which was electroplated on a stainless-steel substrate. Although this material exhibited excellent solar absorption and low emissivity, it degraded significantly under high temperatures.

 To solve this problem, Zäll used Harrick Plasma’s Basic Plasma Cleaner to clean the stainless-steel / cobalt-chromium (SS-Co-Cr) sample. Thanks to this cleaning, the authors successfully deposited a top layer of silica (SiO₂) on the sample by dip coating in a sol solution. Samples with this additional layer exhibited excellent thermal stability while maintaining high solar absorbance. The silica layer also improved the overall adhesion of the sample under ASTM D3359 crosshatch testing.