Thermo-mechanical life assessment of solar central receivers: Comparison of coarse and fine grid discretisations

This paper deals with the thermomechanical analysis of a molten-salt tubular central receiver in a solar power tower plant using three discretization levels. A coarse-grid model (CGM) considers one representative tube per panel; a fine-grid model (FGM) is run first with the CGM mass-flow setpoint and then with adjusted mass flow to achieve a 565°C outlet. We compare mass flows, temperatures and elastic stresses on the spring equinox, summer solstice, and winter solstice. They serve to assess the receiver durability as equivalent operating days (EODs) resulting from creep-fatigue damage. The CGM systematically overpredicts the heat transfer fluid flow that the receiver can heat up to 565°C compared to the FGM. Moreover, while panel-average temperatures are captured reasonably, the CGM misses tube-to-tube gradients, and yields higher tube temperatures overall, which amplifies elastic stress error from around + 30% to −15%. The largest error occurs at mid-panel height, which is typically the critical spot durability-wise. For large storage sizes (∼30000 tn), the CGM underestimates panel 1 life in 7.27 years versus the FGM with adjusted flow rate, suggesting unnecessary repairs. In the remaining panels the CGM overpredicts durability, risking earlier-than-predicted failures. In the most concerning panels (2–4) it is up to 2 years. These discrepancies arise from the interplay among temperature, elastic–plastic stress, and stress relaxation. Overall, tube- and panel-level variability undermines generalization from a single representative tube. If a CGM must be used, panel-specific safeguards are recommended; otherwise, the FGM with adjusted flow provides more credible life and cost forecasts.