In-situ heat loss measurements of parabolic trough receivers based on transient infrared thermography

The design lifetime of parabolic trough receivers is at least 25 years. However, depending on the specific operating conditions, this expected lifetime may be shortened. A periodic inspection of receivers mounted in a solar field is thus recommended. Several field methods with distinct depth of information and field throughput exist to estimate receiver thermal performance. This paper gives an overview of these field methods and presents the application of a transient infrared thermography method, which combines dynamic temperature measurements with a numerical heat transfer model in order to derive specific receiver heat losses and separate internal heat loss mechanisms. This method has been previously investigated under laboratory test conditions and is here applied under field test conditions for in-situ thermal measurements on mounted receivers. The transient thermography method allows a correct estimation of specific heat losses within a precision range below ±10% for all tested receivers under field test conditions. Relevant separation of heat loss mechanisms could be derived for evacuated PTRs with solar selective absorber coating, while partially based diagnoses could be observed for partially or non-evacuated PTRs with highly emissive absorber coatings. Active thermography is considered as a relevant tool for receiver field inspection, in combination with a complementary field screening measurement technique