Solar spectrum energy distribution

Langley, S.P., The distribution of energy in the normal solar spectrum, Compt. rend., 93, 140-3, 1881. 

Table 1 Energy distribution in the terrestrial solar spectrum (AM 1.5)...

Fig. 9. Absorption spectra of chlorophylls a and b, p-carotene, phycocyanin and phycoerythrin the overlaid spectrum (thick-line) is that of solar-energy distribution at earth s surface.

It is well known that the spectral distribution and irradiance of the solar radiation at the Earth s surface depend on the location and is subjected to seasonal and diurnal variations. Therefore, a reference spectrum is needed as a basis for comparison with the spectral energy distribution of artificial light sources. Data from CIE No. 15 1971 (colorimetry official recommendations of the International Commission on Illumination) that recommend a standard illuminant D65 with a scheduled color temperature of approximately 6500 K have been used as a basis over the years. 

The solar spectrum outside the Earth s atmosphere extends from about 200 nm to 2500 nm, half of the energy being concentrated in the visible part of the spectrum, 40% in the infrared, and 10% in the ultraviolet. Practically all the radiation below 295 nm is. filtered out by the atmosphere so that the solar energy reaching the Earth s surface is distributed according to the spectrum shown in Fig. 1 [1]. 

The elemental composition of our sun is about 73% hydrogen, 25% helium, and 2% carbon, nitrogen, oxygen, and other elements distributed as shown in Figure 17.2. In all, approximately 70 elemrats have been detected in the solar spectrum and diere are reasons to believe that all the elements to uranium are present in our sun. Let us now consider the reactions for the formation of all these elements and the energy producing nuclear processes in our sun and other stars. 

These spectrumraltering dyes would be applied in a non-absorbing matrix to the solar incident side of existii photovoltaics. The result would be tiut the spectral distribution of photons inci nt on tiie photovoltaic device would differ from that of the incoming solar spectrum. Thus, the dye would alter the solar spectrum in-line (see Figure 1) with no area concentration of energy. 

By now, it was becoming clear that there was a connection between electrons in bodies, the radiant energy emitted by those bodies, and the distribution of that energy in the spectrum. But a more detailed theory with more information was needed. Rutherford had proposed an atom modeled on the solar system, with electrons orbiting around a positive nucleus and a lot of empty space between the electrons and the nucleus. In 1913 the Danish physicist Niels Bohr (1885-1962), who worked with Rutherford for four years and on his return to Copenhagen made Denmark a world center of theoretical physics, published one of the twentieth century s most important papers. He applied Planck s equation and the notion of quantization of energy to Rutherford s... 

It is quite apparent from Fig. 8-63 that solar radiation which arrives at the surface of the earth does not behave like the radiation from an ideal gray body, while outside the atmosphere the distribution of energy follows more of an ideal pattern. To determine an equivalent blackbody temperature for the solar radiation, we might employ the wavelength at which the maximum in the spectrum occurs (about 0.5 /im, according to Fig. 8-63) and Wien s displacement law [Eq. (8-13)]. This estimate gives... 

The hemispherical total absorptivity is not only a property of the absorbing surface. Rather, it depends on the spectral distribution of the incident radiation energy. This is shown by the different values of a for the mainly short-wave solar radiation, in which the absorption properties at small wavelengths are decisive, and for the incident radiation from an earthly source, for which the long-wave portion of the absorption spectrum a (X,T) is of importance. 

The sun emits radiation whose frequency distribution is closely similar to that predicted for a blackbody radiator at 5900°K (Figure 1.5). It essentially begins in the vacuum UV at about 120 nm, rises to a maximum at 400 nm at the beginning of the visible spectrum, and falls gradually through the visible and infrared regions. The total amount of solar energy received at the earth s surface is about 1370 J/mVsec, and a quantity approximately equal to this is either reflected back into space or absorbed by the atmosphere. 

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