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The Linear
Fresnel Collector is an attractive option for solar thermal power
stations, as shown by previous projects and fea-sibility studies. MAN
Ferrostaal Power Industries is currently erect-ing a demonstration
collector in cooperation with Fraunhofer ISE and DLR at the Plataforma
Solar de Almeria. To ensure industrial production lines and
qualification, Fraunhofer ISE is developing measurement techniques for
industrial application of Fresnel collectors and adapting them to their
special properties and geometries in a German national project called
FRESQUALI.
Optical and thermal qualification will help manufacturers and
construction companies to control collector performance as stipulated in
the specifications. Some properties of the key components, i.e., thermal
receiver, secondary and primary mir-rors, still have to be determined.
the first months of the project, a reflectometric technique was adapted
to the requirements of solar field characterization. With strip
reflection, the shape and optical aberrations of curved mirrors can be
determined from camera pictures. Laboratory measurements using active
pattern generation with projectors or flat screens have been developed
to qualify the primary and secondary mirrors during production at the
PSA. At the moment, a passive pattern technique using a printed pattern
with sinusoidal grey strips is being developed for outdoor
characterization of mounted mirrors. The technique is very flexible and
may be adapted to parabolic mirror fields also.
Dust and dirt as well as degradation of mirrors may also re-duce the
output of solar thermal fields and have a noticeable impact on their
economics. A mobile spectrometer is to be used for fast reflectometric
characterization in a handheld device.
A special 3.4 µm wavelength thermal infrared camera can be used to study
the temperature distribution of solar receivers behind the glass cover
for non-destructive testing of absorber properties.
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