Performance of a parabolic trough solar collector
Date
2005-03
Authors
Brooks, Michael John
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
Parabolic trough solar collectors (PTSCs) constitute a proven source of thermal energy for
industrial process heat and power generation, although their implementation has been strongly
influenced by economics. In recent years, environmental concerns and other geopolitical
factors have focused attention on renewable energy resources, improving the prospects for
PTSC deployment. Further work is needed to improve system efficiencies and active areas of
research 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 been
developed locally for use in an ongoing PTSC research programme. The aim of this study
was to test and fully characterise the performance of the collector.
Specialised logging software was developed to record test data and monitor PTSC
performance in real-time. Two heat collecting elements were tested with the collector, one
unshielded and the other with an evacuated glass cover. Testing was carried out according to
the ASHRAE 93-1986 (RA 91) standard, yielding results for the thermal efficiency, collector
acceptance angle, incidence angle modifier and collector time constant. Peak thermal
efficiency 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 heat
loss coefficient by 50.2 % at maximum test temperature. The collector time constant was less
than 30 s for both receivers, indicating low thermal inertia. Thermal loss tests were conducted
and performance of the trough’s tracking system was evaluated. The measured acceptance
angles of 0.43° (unshielded) and 0.52° (shielded) both exceeded the tracking accuracy of the
PTSC, 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, which
showed potential for predicting trough performance under forced convection conditions.
Description
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2005.
Keywords
Dissertations -- Mechanical engineering, Theses -- Mechanical engineering, Parabolic troughs, Solar collectors