Dynamic Behavior of Solar Radiation
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Dynamic Behavior of Solar Radiation Teolan Tomson, Viivi Russak and Ain Kallis
1 Introduction This chapter is addressed mainly to engineers working on utilization of solar energy converted from the global radiation. Authors expect that the reader is acquainted with fundamentals and terminology of solar engineering (explained for instance in Duffie and Beckman 1991). Global (or: total) solar radiation is the sole energy carrier for the whole nature. Fossil fuels are in fact chemically stored primeval solar radiation. Yet more - thermal stresses and fatigue due to changing insolation involve the destruction of the lithosphere and they also participate in the development of (desert) landscape. Variability of the insolation has to be considered in the solar engineering too and it is analyzed in this chapter with different approaches. Utilization of the solar energy is mostly supported and limited with its storing, which has to be based on the consideration of the dynamical behavior of solar radiation. Fatigue effects mentioned above assess the life-time of materials used and should be considered in solar engineering (Koehl 2001; Carlson et al. 2004). Solar radiation on the infinitely (in practice – sufficiently) long time axis is a stationary ergodic process that includes both periodical and stochastic components. It remains always in the interval between zero and some upper value not exceeding the solar constant. Still, solar radiation could be a non-stationary process during some shorter time interval, intended for practical problem-solving. Periodical component has the astronomical and stochastic component has the meteorological origin. Figure 10.1 shows the yearly diagram of the (relative) normal Teolan Tomson Tallinn University of Technology, Estonia, e-mail: [email protected] Viivi Russak Tartu Observatory, T˜oravere, Estonia, e-mail: [email protected] Ain Kallis Tallinn University of Technology, Estonia, e-mail: [email protected]
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Fig. 10.1 Normal extraterrestrial solar irradiance G0n ∗ is a periodical variable
extraterrestrial irradiance (Kondratyev 1969), which is a result of the elliptic trajectory of the Earth around the Sun. Other small variations of the solar constant have second order meaning (e.g. Duffie and Beckman 1991). Declination caused by the slope of the Earth‘s axis with regard to the elliptic path about the Sun and rotation of the Earth involves additional periodical changes of solar radiation. These processes assess the yearly periodical component. Diurnal periodical component is assessed by rotation of the Earth. The state of the atmosphere involves both stochastic and periodical changes. The turbidity of the atmosphere and cloud cover has mainly stochastic origin, but not only. Periodical monsoon seasons in tropical areas are well known. Less attention has been paid to the trajectories of Atlantic (Prilipko 1982) and Arctic (Br¨umer et al. 2000) cyclones (Fig. 10.2) over Northern Europe (Scotland, Scandinavia, the Baltic states and North-West Russia), which have also
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