In solar energy, people pay attention to the solar irradiance that can be intercepted at a spot on earth. The size of solar irradiance depends on the following four aspects.

(1) daily distance;

(2) the relative position of the sun at some point on the earth;

(3) attenuation of solar radiation into the atmosphere;

(4) the azimuth and inclination of solar energy receiving surface.

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Spectral distribution of solar radiation.

Solar radiation is an electromagnetic wave radiation, that is, there are volatility, there are particles, its main wavelength range of spectral (0.15 4 um, while the ground and the main atmospheric radiation wavelength range for 3 ~ 120 um. In meteorology, according to the different wavelengths, usually called the solar radiation shortwave radiation, and called the atmospheric radiation and the ground long-wave radiation.

Spectral wavelength division of solar radiation: wavelength is less than 0.4pum for ultraviolet band: from 0.4-0.75.um to visible band, and the wavelength is greater than 0.75um for infrared band. In the wavelength range of the visible spectrum, the electromagnetic radiation of different wavelengths produces different color perception to the human eye. Table 1-1 lists the wavelengths and spectral ranges of various colors.

The wavelength and spectral range of various colors.

WeChat picture _21. PNG.

The spectral energy distribution curve of the solar spectrum is shown in FIG. 1-3. As can be seen from the figure, although the wavelength range of solar radiation is relatively wide, most of the energy is concentrated in.22~ 4.0 PM, which is 99% of the total energy. Among them, the visible band is about 43%, the infrared band is about 48.3%, and the ultraviolet band is about 8.7%. The corresponding wavelength of the maximum energy distribution is 0.475um, which belongs to blue-green light.