The capability of thermotropic glazing to reduce stagnation temperatures in solar thermal collectors is evaluated in in-situ testing (south-façade of an office building). Therefore, a thermotropic formulation which is curable by sunlight and which exhibits both, excellent light-shielding characteristics (transmittance reduction by ~20%) and long-term stability is specifically designed. Application relevant overheating protection efficiency is given: absorber temperatures are reduced by up to 29 K in collector stagnation. Performance characteristics are not changed during the six month period of in-situ testing. The application demonstration emphasizes the high innovative capacity of thermotropic materials.