Fabric solar reflectance

It has been known for some time that the color of fabrics and the types of dyes used can be important factors in determining the solar reflectance of fabrics (15., l6). However, color of fabrics in apparel has no effect on the loss of body heat since the color of a fabric has a small effect on its surface emittance (16). Other factors such as fiber orientation and length, yarn twist, and fabric structure also influence the infrared and visible reflection properties of various fabrics (17). In a recent study, the various radiant properties of textiles measured at the peak emission wavelength of sunlight (0.6 urn), were found to approach constant values of absorptivity (0.67), absorptance (0.33), transmissivity (0.0), and reflectivity (0.33) at infinite superficial density (3.) ... 

Figures 7.5 and 7.6 give the measured spectral reflectances and transmittances of fabrics. It is clear from Figure 7.5 that color (6,white 7,black 1,yellow) has a significant effect in reflecting solar irradiance, and also we see why these colors can be discriminated in the visible spectral region of 0.6 pm. However, in the spectral range relevant to fire conditions, color has less of an effect. Also, the reflectance of dirty (5a) or wet (5b) fabrics drop to <0.1. Hence, for practical purposes in fire analyses, where no other information is available, it is reasonable to take the reflectance to be zero, or the absorptivity as equal to 1. This is allowable since only thin fabrics (Figure 7.6) show transmittance levels of 0.2 or less and decrease to near zero after 2 pm.

Methods have been developed for fabrication of the highly-ordered titania nanotuhe arrays from titanium thin films atop a substrate compatible with photolithographic processing, notably silicon or FTO coated glass [104]. The resulting transparent nanotuhe array structure, illustrated in Fig. 5.16, is promising for applications such as anti-reflection coatings and dye sensitized solar cells (DSSCs). Fig. 5.17 shows the typical anodization behavior of a 400 nm Ti thin film anodized at 10 V in an HE based electrolyte. Eor a fixed HE concentration, the dimensions of the tube vary with respect to... 

Figure 14.2 illustrates the relationship between the maximum SPF and the cover factor. Using a SPF value of 50 as the goal, a fabric with a cover factor of 0.98 and composed of fibres that absorb all of the non-reflected UV radiation will provide its wearer with excellent protection against solar UV radiation. 

Fresnel Lenses. Fresnel lens concentrators have been studied for both theimial and photovoltaic systems. The economic viability of their use depends on a large number of system-related factors, Including the performance, cost, and durability of the lenses. Performance requirements Include minimum absorption, scattering, and surface reflection. Total cost depends on costs of materials and fabrication, or minimum thickness defined by mechanical requirements, and on additional material required for optical design. Like other solar applications of optical polymers, durability for extended periods Is required. 

Transparent polymer solar cells (i.e., polymer solar cells with transparent electrodes) can be easily fabricated based on inverted architecture and have important application in tandem architectures as well. We can form transparent solar cells by replacing the Al top electrode with 12 nm Au in the inverted structure. The J-V curves for this transparent polymer solar cell, with light incident from ITO and Au side, are shown in Figure 11.17. The difference between the two J-V curves is due to the partial loss by the reflection and absorption at the semitransparent Au electrode. To provide sufficient electrical conductance, Au layer thickness has to be sufficient and the optical loss at Au electrode becomes significant. However, the inverted solar cell structure has the V2O5 layer which is not only transparent but also provides effective protection to the polymer layer. A transparent conductive oxides electrode, such as ITO, can therefore be deposited without compromising device performance. 

Porous silicon consists of silicon and air. The refl"aetive index of PS can be ehanged between refractive index of silicon (nsi = 3.84) and air (n = 1) depending on porosity. Reflectance of PS can be controlled by change of porosity during eleetroehemical fabrication by change of etching conditions (Perez 2007). For a dedicated review, see handbook chapter Refractive Index of Porous Silieon. It facilitates the application of PS layers on silicon as an ARC in solar cells. 

Data on reflectance of single-layer PS, double-layer PS, and combined layers used in silicon solar cell fabrication are given in Table 1. 

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