Partially shaded heat collector element - A practical approach to performance improvement

Abstract

In this paper, we introduce a partially shaded heat collector element (PSHCE), created by covering a reflective coating at the upper part of the glass envelope, for use in solar parabolic trough systems. Analysis based on a detailed two-dimensional model shows that this novel approach achieves an effective reduction of radiative heat losses from the absorber tube. The total heat loss is reduced in two working conditions, V (vacuum in annulus) and A (air in annulus), by 15.07% and 8.55%, respectively, compared to the prototype (LS-3). Greater optimization accounting for the effects of the PSHCE's rim angle (θrim) and tube radius ratio (γ) further strengthens this response. Multi-parameter optimization allows the total heat loss reductions for V and A to reach 29.87% and 20.05%, respectively, compared to the LS-3 prototype. In case V, the thermal efficiency (η) increases from 68.89% to 71.70%. In case A, (η) increases from 63.72% to 65.36%. These results demonstrate that a partially covered coating could be an effective and practical approach to improving the thermal efficiency of solar parabolic trough systems.