Performance of a parabolic trough solar collector

[摘要] Parabolic trough solar collectors (PTSCs) constitute a proven source of thermal energy forindustrial process heat and power generation, although their implementation has been stronglyinfluenced by economics. In recent years, environmental concerns and other geopoliticalfactors have focused attention on renewable energy resources, improving the prospects forPTSC deployment. Further work is needed to improve system efficiencies and active areas ofresearch include development of advanced heat collecting elements and working fluids,optimisation of collector structures, thermal storage and direct steam generation (DSG).A parabolic trough collector, similar in size to smaller-scale commercial modules, has beendeveloped locally for use in an ongoing PTSC research programme. The aim of this studywas to test and fully characterise the performance of the collector.Specialised logging software was developed to record test data and monitor PTSCperformance in real-time. Two heat collecting elements were tested with the collector, oneunshielded and the other with an evacuated glass cover. Testing was carried out according tothe ASHRAE 93-1986 (RA 91) standard, yielding results for the thermal efficiency, collectoracceptance angle, incidence angle modifier and collector time constant. Peak thermalefficiency was 55.2 % with the unshielded receiver and 53.8 % with the glass-shielded unit.The evacuated glass shield offered superior performance overall, reducing the receiver heatloss coefficient by 50.2 % at maximum test temperature. The collector time constant was lessthan 30 s for both receivers, indicating low thermal inertia. Thermal loss tests were conductedand performance of the trough's tracking system was evaluated. The measured acceptanceangles of 0.43° (unshielded) and 0.52° (shielded) both exceeded the tracking accuracy of thePTSC, ensuring that the collector operated within 2 % of its optimal efficiency at all times.Additionally, experimental results were compared with a finite-volume thermal model, whichshowed potential for predicting trough performance under forced convection conditions.

[发布机构] Stellenbosch University