Parabolic troughs

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... 

Fig. 10. (a) One configuration of an optical-type concemrator with axial absorber (b) parabolic troughs under test for various uses, including irrigation pumping for croplands... 

The photovoltaic static parabolic trough concentrator module has been developed in the All-Russian Research Institute for Electrification of Agriculture (VIESH) for stand-alone and large-scale applications [9]. 

For production cost estimation of PV parabolic trough concentrator module several assumptions were made ... 

A 354 mW thermal solar plant at Kramer Junction in the Harper Valley in California that has been in operation since 1985 (courtesy of NREL/DOE). (Top) This is one of nine solar electric energy-generating plants at Kramer Junction, California and it uses parabolic troughs to collect the Sun s energy. (Courtesy of National Recoverable Energy Laboratory-NREL/DOE.) (Bottom) In the receiver tubes, hot oil transports the concentrated solar heat to steam boilers, which drive the turbine generators. 

The first concentrating trough-type solar power plant in the United States was built in 1988. It is the 1 mW Saguaro plant located north of Tucson, Arizona, and was built for Arizona Public Service (APS). It covers 1 km2 and has parabolic trough-shaped mirrors. 

Power Tower — Similar in principle to parabolic-trough technology, the mirrors are placed in a circular pattern. At the center of the circle is a tower, at the top of which is a receiver filled with water, air, liquid metal or molten salt that moves to a power block and is used to power a steam turbine. 

U.S. and one industrial waste water treatment in Spain. Engineering scale field experiments have been conducted by the National Renewable Energy Laboratory (NREL) at the Lawrence Livermore National Laboratory (LLNL) treating ground water contaminated with trichloroethylene (TCE) [253]. This field system consisted of 158 m2 of parabolic trough reactors and used De-gussa P25 particles (0.1%) as the photocatalyst in a slurry flow configuration. With this relatively low titanium dioxide content the TCE concentration was reduced from 200 ppb to less than 5 ppb. 

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. 

Figure 1 Parabolic trough photocatalytic reactor at Plataforma Solar de Almerla (reprinted from Malato et al., 2007 with permission from Elsevier).

Figure 8 Reaction rate optical factor as a function of catalyst concentration for a parabolic trough solar photocatalytic reactor. Adapted from Arancibia-Bulnes and Cuevas 2004, with permission from Elsevier.

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... 

Malato et al., 1997) as mentioned previously. These features were confirmed in several studies using CPC and other nonconcentrating reactors as well as parabolic troughs (Cured et al., 1996b Gimenez et al., 1999 Malato et al., 1997). 

The MCM has been used to simulate tubular solar photocatalytic reactors, like parabolic troughs (Arancibia-Bulnes et al., 2002a), CPC (Arancibia-Bulnes et al., 2002b), and also of flat plate geometry (Cuevas et al., 2004). Also it has been used to simulate flat lamp reactors (Brucato et al., 2006) or to obtain optical coefficients by comparison with transmission results from an experimental cell (Yokota et al., 1999). 

As discussed previously, several solar photoreactor geometries can be reduced to cylindrical glass tubes externally illuminated by different types of reflectors, like parabolic troughs, CPC, V-grooves, or without reflector, directly illuminated by the sun. In this section the general solution of the PI approximation for this t)q5e of photo reactors is reported. This general solution is applicable to any particular reactor if the flux distribution impinging on the wall of the tubular reaction space is known. 

Figure 17 Geometry of the parabolic trough and reactor tube (a), and coordinate systems inside the tube (b) (reprinted from Arancibia-Bulnes and Cuevas, 2004, with permission from Elsevier).

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