Experimental investigations show that if thermal efficiency is plotted

Fig. 1. Schematic of the receiver. Note the RTD (resistance temperature detector) inserted at the far end of the receiver.Figure optionsDownload full-size imageDownload as PowerPoint slide
Table 3.
Thermal/optical properties of the elements of UNIVPM.01. Optical properties were evaluated at normal incidence conditions. Note that, with the exception of specular reflectance ρn, other properties were derived from the literature.PropertySymbolValueCover transmittanceτn0.93Absorber absorptanceαn0.95Foil specular reflectanceρn0.94Absorber conductivity (W m−1 °C−1)λa237Full-size tableTable optionsView in workspaceDownload as CSV
With such a receiver, the concentration ratio C, i.e., the ratio between the aperture area of the collector Aa and the absorber outer surface Ar, MK-2206 [14]:equation(1)C=AaAr=1.850.20=9.25.
2.2. Manufacture of the fiberglass/XEPS parabola
The parabolic support structure was made with a composite of extruded polystyrene (XEPS) within a fiberglass shell. The mechanical and chemical characteristics of fiberglass are well known: this material was used for the first time for the construction of PTCs by Kalogirou et al. [4]. XEPS, however, is not as common in composite materials, but it has several advantages: a) it is very economical; b) it is light (its surface density is ?200 kg m−2); c) it presents good mechanical properties. It has a high resistance to compression from evenly distributed forces, so it is very suitable for use in a sandwich structure. It is widely used in buildings for thermal insulation and is therefore sold in sheets of various dimension and thickness. Different varieties of polystyrene are used in construction, but the extruded one presents the best mechanical properties at a low price (about 2.5 EUR m−2 for 40 mm thick sheets).