Solar Thermal Energy 1 Solar Radiation 9 A

Solar Thermal Energy

1 - Solar Radiation

9 A sphere of hot gases. 1. 39 x 10 m Dia that have 3 zones: - Core: 0. 23 R - T = 8 – 40 M K - (Nuclear fusion reactor) - Transition: 0. 7 R (from core to conv. Zone) - Convection zone: - T = 130, 000 K down to 5000 K - The outer shell of the convective zone is called the Photosphere - which is the source of most solar radiation Note: - Outside of the photosphere there are 3 layers: - Reversing layer cooler than photosphere - Chromosphere T starts to increase above 5000 K - Corona T up to 5 000, 000 K - Yet we are not affected by this temp, since those layers are of very low density The Sun

THE SOLAR CONSTANT

Solar Constant Definition: The solar constant Gsc is the energy from the sun per unit time received on a unit area of surface perpendicular to the direction of propagation of the radiation at mean earthsun distance outside the atmosphere. WRC adopted value of 1367 W/m 2

VARIATION OF EXTRATERRESTRIAL RADIATION Variation of the earth-sun distance, however, does lead to variation of extraterrestrial radiation flux in the range of ± 3. 3%. The dependence of extraterrestrial radiation on time of year is shown in Figure 1. 4. 1. A simple equation with accuracy adequate for most engineering calculations is given by Equation 1. 4. 1 a. Spencer (1971), as cited by Iqbal (1983), provides a more accurate equation (± 0. 01%) in the form of Equation 1. 4. 1 b: