Philipp Good

Analysis of Conduction Heat Loss From a Parabolic Trough Solar Receiver with Active Vacuum by Direct Simulation Monte Carlo

Results are reported of a numerical analysis of conduction heat loss from a parabolic trough solar receiver with controlled pressure within the annular gap between the tubular absorber and the glass vacuum jacket. A direct simulation Monte Carlo (DSMC)model of rarefied gas within the annular gap is coupled to radiation heat transfer for directional- and spectral-dependent concentrated incident solar radiation. This modeling approach is valid for high Knudsen numbers, and consistently predicts slightly higher heat loss than a continuum model using slip boundary conditions in the range of pressures of interest around 1 Pa. 3-D simulations of axial flow through the annular gap predict higher gas conductance by the DSMC method than by slip flow models, with values converging as pressure increases.

Nonparabolic solar concentrators matching the parabola

We consider the limit of geometric concentration for a focusing concave mirror, e.g., a parabolic trough or dish, designed to collect all radiation within a finite acceptance angle and direct it to a receiver with a flat or circular cross-section. While a concentrator with a parabolic cross-section indeed achieves this limit, it is not the only geometry capable of doing so. We demonstrate that there are infinitely many solutions. The significance of this finding is that geometries which can be more easily constructed than the parabola can be utilized without loss of concentration, thus presenting new avenues for reducing the cost of solar collectors. In particular, we investigate a low-cost trough mirror profile which can be constructed by inflating a stack of thin polymer membranes and show how it can always be designed to match the geometric concentration of a parabola of similar form.

A 3 MWth parabolic trough CSP plant operating with air at up to 650 °C

Parabolic trough concentrating solar power (CSP) has long proven to be among the most viable options for large-scale solar electricity generation. However, conventional solar parabolic trough plants suffer from several technical and economical drawbacks. These include most notably a maximum operating temperature limited to below 450 °C, a difficulty in creating rigid metallic support structures with large trough apertures, and the need for complex thermal energy storage (TES) technologies. This has impelled the development of a novel trough-based CSP system comprising a 9 m aperture parabolic trough concentrator based on inflated metallized polymer films mounted on a concrete support structure, coupled to a solar receiver based on air as heat transfer fluid and to a packed bed of rocks sensible heat storage. The first power plant with this technology, with a nominal thermal power output of 3 MWth, has been constructed in Ait Baha, Morocco. We report on the details of the system and its components.