Parabolic trough collectors

During 1990 several R D activities were started in collaboration with CIEMAT, specifically in the proyect ACE-20. This project consisted in the design, manufacture and assembly of a parabolic-trough collector applied to a desalination plant. 

The aim of the solar thermal collector development is to improve and optimize them for the temperature level from 80 °C to 250 °C. There are different approaches like double-glazed flat plate collectors with anti-reflection coated glazing, stationary compound parabolic concentrator (CPC) collectors, evacuated tube collectors, vacuum flat plate collectors, small parabolic trough collectors, linear concentrating Fresnel collectors and a concentrating collector with a stationary reflector. 

Figure 13. Schematic of reactor collection of direct and scattered ( diffuse) near UV radiation for flat plate (left) and parabolic trough collector geometries (right). Plate collects Ip=I(j+Is, whereas trough reactor collects...

A historical introduction into the uses of solar energy was attempted followed by a description of the various types of collectors including flat-plate, compound parabolic, evacuated tube, parabolic trough, Fresnel lens, parabolic dish and heliostat field collectors (Kalogirou, 2004a, 2004b). Solar thermal electricity systems utilize... 

Concentrating collectors are only able to use a limited fraction of fhe diffuse solar radiation. This utilizable fraction can be estimated as the inverse of the concentration ratio of fhe collecfor (1/Cr) (Rabl, 1985). Because of this, parabolic trough photocatalytic reactors, which have a concentration ratio around 15 or higher, miss practically all diffuse radiation. This amounts to losing around half of fhe available UV solar irradiance. 

More recently, reactors based on nonimaging collectors, like the CPC, have attracted interest (Blanco et al., 1999). These reactors share some of the advantages of both parabolic troughs and nonconcentrating reactors... 

Three main types of concentrating collectors have evolved for use in solar thermal systems low concentration parabolic troughs, high concentration parabolic dishes, and central receivers (Fig. 3). Higher concentration produces higher temperatures in a working fluid and makes electrical generation more efficient. 

The assumed conditions used in evaluating characteristics of the systems are summarized in Table 2. The total areas of the solar collectors and photovoltaic arrays are assumed to be 10 ha. In the solar thermal and hybrid systems, the type of collector is parabolic trough, the condenser outlet pressure 0.1 kg/cm a, and the capacity (maximum net power output) has been determined so as to minimize the unit cost of generated power energy. In the solar photovaltaic system, the conversion efficiency at the array is assumed to be 15 %. The tracking scheme of the solar collector and photovoltaic array is single north-south axis. 

Collector ACE20, CIEMAT Parabolic-Trough System... 

Polymeric materials are used In all solar technologies. In addition to such conventional applications as adhesives, coatings, moisture barriers, electrical and thermal Insulation, and structural members, polymers are used as optical components In solar systems. Mirrors on parabolic troughs are made up of metallized fluoropolymers and acrylics. Commercial flat-plate collectors are glazed with fluoropolymers and ultraviolet-stabilized polyester/ glass fiber composites. Photovoltaic (PV) cell arrays are encap-... 

More sustainably, modern solar collectors instead of artificial lamps are used [50]. Many solar parabolic trough reactors can be used both on laboratory and industrial scales, for example, at the German Aerospace Centre (DLR) in Cologne. 

Adhesives (128) play an important role in the construction of a solar parabolic trough reflector. The adhesives should be compatible with silvered glass mirrors and should be able to carry structural loads. Moreover the adhesives should be durable for at least twenty years without losing their properties. Adhesives screened for solar collectors were epoxies, urethanes, and acrylics. Three types of stress conditions were identified as the most likely causes of failure in the trough modules ... 

FIGURE 13 Comparative peak performance for a tracking parabolic trough, an ISEC, contemporary (external reflector) evacuated CPCs (triangles) and flat plates. The ISEC s superior performance up to temperatures above 200°C, achieved with no moving parts, makes it an extremely flexible solar thermal collector. 

Y.-L. He, J. Xiao, Z.-D. Cheng, Y.-B. Tao, A MCRT and FVM coupled simulation method for energy conversion process in parabolic trough solar collector. Renewable Energy 36(3), 976-985 (2011)... 

Fig. 7.3 Main types of photoreactors used for water and wastewater treatment (irradiated by sun or UV lamps) (a) compound parabolic collector (CPC) (b) parabolic trough reactors (PTR) (c) double-skin sheet reactor (DSSR) (d) slurry, wall, fixed bed reactor (e) batch reactor with outer source of irradiation and (f) batch reactor with inner source of irradiation...

Compound parabolic collectors (CPCs) belong to the most promising photocatalytic solar reactors which combine the advantages of parabolic trough concentrator and non-concentrating system [178]. CPCs are low-concentration static collectors with reflective surface and can be designed for any given reactor shape (see Fig. 7.3a) [182]. The CPC reflectors are usually made from polished aluminum... 

The most common solar collector is the glass-covered flat plate type. Others include concentrating trough and tube-over-reflector collectors, and parabolic collectors. A flat plate collector uses a flat black absorber plate in a container box. Insulation behind the absorber plate and on the sides of the box reduce heat loss. The glazing may be flat glass, translucent fiberglass or clear plastic, on the sun side of the collector, 1 to 2 inches above the absorber. 

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