Solar blind pyrometric temperature measurement on pressurized volumetric power tower receivers

The operation of solar thermal high temperature receivers requires an accurate knowledge of the temperature distribution on critical parts of the receiver. However, concentrated solar radiation makes it difficult to determine the temperature on irradiated surfaces. Contact thermometry is not appropriate for the use under concentrated solar radiation and also pyrometry fails when external light sources interfere significantly. To avoid distortion of the temperature reading, the measurement has to be performed in a spectral range where the emitted thermal radiation exceeds the reflected solar radiation by a multiple. The measurement in solar blind spectral regions of atmospheric absorption bands offers one possible solution of filtering the solar radiance from the measurement signal. Along with the intensity of the incoming solar radiation and the absorber emittance, the bidirectional reflection properties and the temperature of the object determine the required selectivity of the spectral filter. In atmospheric absorption bands, the influence of the atmospheric absorption on the measurement signal cannot be neglected even for small path length. The paper describes the methods of solar blind pyrometric temperature measurement on solar thermal high temperature receivers and shows the possibilities and limitations of accounting for the atmospheric absorption with models based on radiation transfer calculations. Finally, experimental results recorded with an infrared mirror scanner especially designed for the measurement on a pressurized volumetric receiver are presented and compared to thermocouple readings and results of a thermodynamic model of the receiver.