Solar Radiation Calculation Methods In Different Altitudes

Solar radiation is not only an important energy for all of activities on Earth, but also the most important factor of the Earth’s climate, and has played a decisive role to maintain the surface radiation balance and influence the formation of weather and climate. The changes of solar radiation have a very important impact in climate change, agricultural production and daily life. At present, the energy crisis is getting worse, so it has become increasingly important to use of natural resources more efficient. While99.8%of the surface energy comes from solar energy, it is valuable to accurately calculate the solar radiation (including single-wavelength solar radiation and solar irradiance) and determine the temporal and spatial distribution.Although the total meteorological observation stations are over2500, but there are only over100meteorological observation stations which can be used to multiple observe solar radiation, and almost none specially designed for the measurement of solar radiation, so existing measured data used for solar radiation research is far from the needs of solar radiation study. Therefore, solar radiation study often model for the theoretical calculate.Solar radiation formulas proposed by literature generally apply only to sea level or low altitudes, and it is not enough in some solar energy engineering, such as design of solar-powered aircraft, which need solar radiation formulas applying to high-altitude. In view of this situation, so the inhomogeneous atmosphere model is proposed to derive formulas which can be used to calculate single-wavelength solar radiation and solar irradiance at any height-including surface of different altitudes and the atmosphere at different height.Heterogeneous atmospheric model assumes that atmosphere is uniformly mixed, and atmospheric molecular concentration and atmospheric density distributes vertically. According to Beer’s law, the absorption coefficient of the atmosphere satisfies the equation:K(x,λ)=A(λ)n(x), where A(λ) is a constant which is independent of atmospheric molecular concentration and is dependent wavelength, and can been measured by the spectral distribution of sea and outer space; And where n(x) is the atmospheric molecular concentration, and is proportional to the air density p(x). Since the atmospheric molecular concentration and atmospheric density can be calculated, the inhomogeneous atmosphere model can used to derive formulas which can calculate single-wavelength solar radiation and solar irradiance at any height-including surface of different altitudes and the atmosphere at different height.The error by ignoring curvature of the atmosphere is considered, and the correction method is given to reduce error:when zenith angles is less than75°, this error can be ignored, namely solar radiation formulas proposed by the inhomogeneous atmosphere model can be used directly; when zenith angles is more than75°, correction formula can be simplified by linear process.The validation results shows that calculated values are closely consistent with measured data, so the inhomogeneous atmosphere model provides practical value for calculating solar radiation.