Methodology for obtaining instantaneous thermal performance curves for a parabolic trough solar by experimental data and projections based on a ray tracing model

•New methodology for the evaluation of the thermal performance of PTC.•Ray tracing model was applied together with experimental thermal performance curves.•Characterization without two-axis tracking system and regardless of the time of year.•Analysis of the effect of solar declination on a PTC with tracking on a single axis.•Thermal efficiency curves obtained for certain periods of the year or even for each day. Parabolic Trough Concentration (PTC) systems represent the best alternative for implementing solar energy in different sectors due to their reachable temperatures and maturity levels. However, there is a notably lack of normativity for evaluating the experimental thermal performance curves of these systems. For this reason, a new methodology is proposed to solve problems arising in the thermal characterization of them. This methodology allows to evaluate the system at any time of year without a two-axis tracking system, using experimental data and projections based on a ray tracing model. To validate the methodology, a PTC system was evaluated during solstices and equinoxes. Variations in experimental thermal performance response along the year caused by solar declination; were observed, reaching a maximum loss of 45% of received power and 22% in efficiency for the lowest solar altitude conditions. The ray tracing model methodology was applied to the experimental thermal performance curves obtained along the year to get the best efficiency curve. The good approximation of the projections made with this methodology helped us to consider it validated. With this method, it is also possible to easily obtain a family of curves describing the power and performance of the system throughout the year and wherever it is installed.