Integrated solar spectrum

Wavelength range—start, stop, mean radius vector correction, integrated solar spectrum irradiance WLMN, WLMX, SUNCOR, SOLARC... 

The short circuit current is the product of the photon flux (A.) of the incident solar spectrum and the wavelength-dependent spectral response or collection efficiency Q( k) integrated over all wavelengths 7sc = / k)Q k)dX (see Fig. 61b). The collection efficiency is about 80% between 450 and 600 nm, demonstrating that there is little loss due to recombination (the i-layer is of device quality). The decreasing collection efficiency at the red side is due to the decreasing absorption coefficient of a-Si H. In the blue, the decreasing collection efficiency is due to absorption in the /7-layer and/or buffer layer. 

The rate of photolytic transformations in aquatic systems also depends on the intensity and spectral distribution of light in the medium (24). Light intensity decreases exponentially with depth. This fact, known as the Beer-Lambert law, can be stated mathematically as d(Eo)/dZ = -K(Eo), where Eo = photon scalar irradiance (photons/cm2/sec), Z = depth (m), and K = diffuse attenuation coefficient for irradiance (/m). The product of light intensity, chemical absorptivity, and reaction quantum yield, when integrated across the solar spectrum, yields a pseudo-first-order photochemical transformation rate constant. 

Figure 1. Relative spectral responses of different broadband detectors in the UV spectral region. The dashed line corresponds to the CIE action spectrum. The numbers in the legend correspond to the weighted integral (Warm 2) of a standard solar spectrum (30° SZA, 330 DU).

The I- V characteristic shown in Fig. 8 is for a cell with the structure glass/Sn02/p-i-n/Ag, where thep layer is alloyed with carbon (Catalano et al., 1982). The conversion efficiency was 10.1% with Vx = 0.84 V, JK = 17.8 mA cm-2, and FF = 0.676. The spectral response (or external quantum efficiency) of the same 10.1% cell is shown in Fig. 9. An integration of the quantum efficiency with the AM 1 solar spectrum gave a current density of 17.6 mA cm-2, in good agreement with the measured value of JK (Catalano et al., 1982). 

The sum of the direct and the diffuse radiation on a surface. Total solar radiation is sometimes used to indicate quantities integrated over all wavelengths of the solar spectrum. The most conunon measurement of solar radiation is total radiation on a horizontal surface, often referred to as global radiation. 

Finally, the monochromatic accumulation rate Is Integrated over the solar spectrum to obtain the total accumulation rate. The results of this procedure are Illustrated In Figure 1, which shows the variation with depth of the photochemical rate of production of 2 2 midday at 40 N for summer and winter In a freshwater sample. A rapid decrease of Che rate with depth Is apparent, particularly In this dark colored freshwater sample which attenuates most of Che near-ultraviolet radiation In Che upper 20 cm. Figure 2 shows how Che calculated rate of photochemical production varies with time of day and extent of cloud cover at a chosen latitude and season. 

There appear to be 4 main steps to using the solar spectrum, optical property measurements and solar integration ... 

To avoid confusion between IPCE and solar-to-hydrogen conversion efficiency (STH), we should note three critical differences. First, in contrast to IPCE (electrons out/photons in), STH describes efficiency in terms of power (power out/ power in). Secondly, whereas IPCE measurements can be conducted with any calibrated and monochromated illumination source (i.e. it need not be AM 1.5 G illumination that is monochromated as long as the number of impinging photons at each wavelength are counted), STH requires the use of broadband solar-simulated illumination. The reader is referred elsewhere [5] for a discussion of solar simulation using laboratory illumination sources. The integration of IPCE over the entire solar spectrum can provide an estimation of the maximum possible STH, if (and only if) no applied bias is used in the IPCE measurement. Lastly, conducting IPCE experiments with an applied bias is allowable whereas STH requires true zero-bias conditions. Of course, the authors of a publication must be explicit as to... 

Present solid-state (photovoltaic) mul-tijunction photovoltaics exist in one of two modes, either splitting (in which the solar spectrum is optically separated before incidence on the cells) or stacked devices. The latter mode has been developed as either monoKthic (integrated) or mechanically (discrete cells layered with transparent adhesive) stacked cells. Most monoKthic stacked multijunction photovoltaics under development use III-V semiconductors in at least one of the layers and take advantage of the variations in band gap and close lattice match achieved with other related III-V alloys. For example, GalnP has been used as a wide gap top cell, or GaSb and GalnAsP as small gap lower cells, for III-V top-layer multijunction cells other cells use silicon or CIS cells as a lower layer [12-15]. 

With photocatalysis the main problems encountered in the previously examined applications of PVRs are avoided. It is also worth noting that (i) the coupling of photocatalysis with the pervaporation process allows for a complementary exploitation of the solar spectrum. In fact, photocatalysis is normally only able to use its ultraviolet component, while the remaining thermal part of the spectrum can be utilized to heat the fluid and to evaporate the permeate (ii) photocatalysis and pervaporation have common operative conditions liquid solutions (often aqueous solutions), low concentrations of the reactants and consequently of the products, low temperature and atmospheric pressure and (iii) once the type of light source is chosen, photocatalysis is a modular process like pervaporation. Therefore the integration of the two processes is straightforward and advantageous. 

Because of the small percentage of uv present in the full solar spectrum, changes in this important component cannot be detected in measurements of total solar radiation. Therefore, commercial outdoor testing facilities measure and monitor the irradiance of the uv portion alone, both total uv and narrow spectral bands of the uv, in addition to total solar radiation. Total solar uv radiation (TUVR) is typically measured between 295 and 385 nm. Irradiance is reported in watts/square meter (W/m ) and radiant exposure, ie, irradiance integrated over time, is reported in megajoules/square meter (MJ/m ). The average 12-month... 

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