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  TRX Selective Coatings

TRX  Selective Coating

Cu-N/AL Coating

Mo-Al2O3 Coating

Temperature-Efficiency Curve


Advantage of TRX coating


TRX offers two types of Selective Coatings using PVD method

  • CU-N/AL  for operating temperature ≤ 330 C ( 626 F)

  • Mo Al2O for operating temperature ≤ 450 C ( 842 F )

These coatings are applied onto substrate surface by a pollution free  PVD (Physical Vapor Deposition) process . The advanced in-line process monitoring and quality control system is a joint development work between Germany ISE and TRX .  This  system ensures consistency in performance and uniformity in quality in all its coated products  .  In comparison , Black Chrome coating uses electroplating process which causes serious pollution problem , while other evacuated tube manufacturers use PVD process with poorer process control .  TRX selective coating consists of 4 layers , the metal infrared reflector layer , HMVF Cermet layer ( absorbs 70% of energy ) , LMVF cermet layer ( 20% )  and the top anti-reflection layer ( absorbs remaining 3 to 5% ) . 


             4 layers TRX system



The common selective coating offers by other manufacturers using PVD process is AL-N/AL system . It  normally has  9 to 15 layers of Aluminum based cermet . Each layer has different concentration of cermet to absorb specific spectrum of sun energy .  AL is not stable in high temperature and the migration of AL molecules between layers is the main reason for the degradation of performance .

The TRX choice of using Cu or Mo in metal matrix composite is significant as these elements are extremely stable in high temperature environment . Each cermet layer is separated by a transparent Al2O3 film to prevent cross migration of cermet concentration at high temperature .  It's photo-thermo conversion efficiency remains stable even after prolonged exposure in high temperature environment and they are rated to have minimum of 15 years to over 30 years of service life with peak performance .

The resultant TRX selective coating is a full-spectrum absorption coating , capable of absorbing  92 to 96% of sun radiation energy in visible light and infrared band ( 0.38-1.5μm ), and is workable in all weather conditions. The emission rate is extremely low , between 5 to 7% for λ≥1.5μm ( 150 C)

TRX is the leader in this kind of high performance selective coating technology . 25% of European high end  evacuated tube market is produced by TRX . Besides the tubes , TRX also provides coating service for flat plate collector manufacturers under OEM agreements .

  Cu- N/AL Performance Curves
  • Near ideal absorption and emission performance
  • Maintains its efficiency throughout its service life
  • Perfect for high temperature application , up to 330 C ( 626 F )continuous exposure


Mo-Al2O3 Performance Curves

  • Identical to CU-N/Al curve , near perfect characteristic

  • Twice the service life than CU-N/AL

  • Ideal coating material for very high temperature applications , up to 450 C (842 F ) continuous exposure


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Temperature Efficiency Curve

Tm = Mean Temperature of fluid in the collector

Ta  = Ambient Temperature

G   = Solar irradiance taken as 800 watt/m2



TRX selective coatings can be applied on any substrate surface like glass or metal .  Its stability in high temperature environment ensures peak conversion performance is maintained and long service life is expected


It is ideal for applications that require high temperature heat collection like parabolic concentrators .

Flat Plate Collector   


with Black Chrome


α = 92-95          


Є = 15-35


With  Cu-N/AL


α = 92-95


Є = 5-7

  Evacuated Tube Collector

With Al-N/AL        

α = 82-95   

Є = 8 -15

With  Cu-N/AL 

α = 95.2   

Є =5.6                                               



Advantages of TRX Selective Coating

  • Full Spectrum coating with excellent thermal absorption and low emission performance
  • Extremely long life and suitable for medium/high temperature collection .
  • Low/Medium cost of application
  • Lower cost compared with TiNOx with equivalent performance
  • Suitable for evacuated tubes or flat plate heat collectors.
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  Working Temperature

  C  / F

Absorption α % Emission  Є %
New Aged New Aged
TRX         Cu-N/Al 330 / 626 92-96 94.5 5 - 7 6.9
TRX        Mo-Al2O3 450 / 842 92-96   5 - 6  
Al-N/Al ≤150 / 302 82-95 82.2 8 - 15 22
Black Chrome Electroplated ≤150 / 302 90-94   15 - 40  
TiNOx 330 / 626 92-95 5-7

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