Analysis and Experimental Results of Solar-Blind Temperature Measurements in Solar Furnaces

Despite the existence of several possible pyrometric methodologies, temperature monitoring and control of samples heated at the focus of solar concentrators have still not received a universal and perfect solution. Here we present an analysis of solar-blind conditions and experimental measurements that have been carried out at the Odeillo Solar Furnace (IMP-CNRS). The aim here is to test different experimental configurations that can conceptually eliminate the reflected part of the concentrated solar flux. These configurations would allow near solar-blind measurements within the atmospheric absorption bands centered at 1.4 μm and 1.9 μm, and true solar-blind measurements within similar bands centered at 2.7 μm, 4.3 μm, and 6 μm. The parasitic reflected solar flux can be evaluated for each of these bands. In the case of alumina in particular, true solar-blind measurements can also be performed under blackbody conditions over the 8–12 μm band, and this is taken here as a convenient example of application. It is also demonstrated that solar-blind measurements are possible outside of these absorption bands, either by adding an appropriate radiation cutting filter (e.g., a quartz window) or by using an infrared narrow filter centered in a spectral region where the incident flux is negligible due to reflection losses (e.g., at 3.9 μm). The Solar Performance Factor is introduced to characterize the potential of any spectral region vis-a`-vis solar blindness.