Parabolic Trough: 
      an example
                                                                SCHOTT Solar Inc.
 Radiation from the Sun transformed into thermal energy
        Used for Heating air or water/fluid media
        Presentation flow
 Solar thermal applications
 A bit about receiver tube and its design
 Spectral selectivity
 Selective absorbers with examples
 Mechanisms for solar spectral selectivity
 Solar absorber design constraints
   Physical process (RF/DC magnetorn sputtering)
   Chemical process (Sol-gel process)
 Surface engineering for enhanced solar absorption
 Conclusions
   Temperature ranges for solar thermal 
                      applications
                         0
 Low temperature (< 100  C)
    Water heating and swimming pools
                             0
 Medium temperature (< 350  C)
    Space heating or cooling and water desalination
                         0
 High temperature (> 350  C)
    Mechanical energy production and catalytic dissociation of 
                                           0
 water, CSP (concentrating solar power ~ 500  C or more)
       Receiver is an important Component in 
                     Parabolic Trough Collectors
   A receiver should comply with
   Low thermal losses  
         ( vacuum, absorber with low thermal emittance)
    High solar absorptance 
        ( efficient absorber, highly transmitting outer glass tube )
                                evacuated
                                annulus                       selective absorber 
                                                              coating on steel, 
     getter to maintain                                            glass-to-metal-
     vacuum                       cover tube with                  seal              bellow to compen-
                                  anti-reflective coating                            sate expansion
  For power plant with a life span of more than 20 years is required to 
  Match the long operational sustainability.
  Keep maintenance costs low during operation.
  During operation receivers are mechanically and thermally stressed.
   
  Most important issues are:
              Durability of glass-to-metal seal 
                          Stability of vacuum (low hydrogen permeation, appropriate getter)
              Durability of absorber coating 
                          (only small degradation of efficiency acceptable)
              Abrasion resistance of anti-reflective glass coating.