Validation of a parabolic trough solar receiver model based on physical formulation of the absorber total emissivity from its spectral emissivity

Abstract

Concentrating solar power is an important way of providing renewable energy. Model simulation approaches play a fundamental role in the development of this technology and, for this, an accurately validation of the models is crucial. This work presents the validation of the heat loss model of the absorber tube of a parabolic trough plant by comparing the model heat loss estimates with real measurements in a specialized testing laboratory. The study focuses on the implementation in the model of a physical-meaningful and widely valid formulation of the absorber total emissivity depending on the surface’s temperature. For this purpose, the spectral emissivity of several absorber’s samples are measured and, with these data, the absorber total emissivity curve is obtained according to Planck function. This physical-meaningful formulation is used as input parameter in the heat loss model and a successful validation of the model is performed. Since measuring the spectral emissivity of the absorber surface may be complex and it is sample-destructive, a new methodology for the absorber’s emissivity characterization is proposed. This methodology provides an estimation of the absorber total emissivity, retaining its physical meaning and widely valid formulation according to Planck function with no need for direct spectral measurements. This proposed method is also successfully validated and the results are shown in the present paper.