3. Parabolic Trough Collector Concepts

Length [ni]

Figure 31 Time line conventional collectors and module's dimensions

3. 
   Category B: Metal Structures & Sheet Reflectors
   

In category B there are concepts derived from the structural advances of conventional collectors. Included are collectors with space frames and an alternative metallic structure that seek to lighten the weight and reduce the elements per square meter. These collectors aim for a significant costs reduction per module without adjudicating the characteristic performance.

More important than the structural implementation of metals such as aluminum, is the reflector material that replaces the conventional thick glass panels. Three types of products are shown in the included concepts, among them polymeric reflective films and coated aluminum sheets (see also Chapter 2.2 Mirror Materials). Each of these has not only different optical properties, but also other needs of maintenance, assembly and durability properties. Glass mirrors make around 13% of the costs of a solar field and weight around 10 kg/m², e.g. RP2 Flabeg type facet. Aluminum reflectors, e.g. ALMIRR, can weigh 4.8 kg/m² with 4 mm thickness and similar to polymeric films, which are in nominal thickness 0.1 mm, attached to an aluminum sheet surface.

Thanks to the standardization of the profiled tubes and connection nodes, the installation of these collectors does not require assembly jigs. Their structure also allows a more efficient assembly in terms of workmanship (cranes, men power...), reducing the installation expenses.

Collectors in these category target higher concentration ratios to up to 104 in the example of the Large Aperture Trough by enlarging the aperture's width. The suitability for molten salt as heat transfer fluid is also present in the case of the SkyFuelDSP. With regard to the structure both apply aluminum tube space frames.

A further innovative approach is targeted by the Solabolic Trough, with aluminum sheet reflectors mounted by tension cables in the structure. The concept was inspired on hanging bridges as for example the Golden Gate in San Francisco, USA. Two segments of a module were prototyped and showed some structural challenges. These limitations currently imped a large scale deployment of the collector⁷. Therefore the concept is excluded from the evaluation and analysis.

4. 
   Category C: Non-Metallic Materials
   

This category presents parabolic trough collectors implementing (i) composite sandwich structures and (ii) high performance concrete materials. While the first subdivision (i) is more focused on the parabolic aperture structure, the concepts with concrete suggest an overall casting of the main body and the support structures.

A different line of manufacturing, transport and assembly process is demanded for these collectors. The use of alternative materials aims a breakthrough in costs reduction with concrete as a cost efficient and worldwide accessible material. Furthermore the enhancement of the geometric parabolic accuracy and resistance towards strong winds should also be favored with the composite materials. In both cases a significant weight reduction can be achieved and Table 4 sums up the density values of the here alluded materials.

Table 4. Densities and Young's moduli of diverse materials [18]