Page 404 - Advances in Renewable Energies and Power Technologies

2. Solar Energy Resources: Sun Characteristics and Solar Radiation 377

FIGURE 12.3
Theoretical thermal efficiency for different collector technologies.
Courtesy B.B. Hoffschmidt, Receivers for Solar Tower Systems [WWW Document], 2014. URL: http://sfera2.
sollab.eu/networking/announcement-summer-schools/summer-schools/summer-school-presentation-2014.

3
storage as well as the average electrical power produced by the plants. They found
the utilization of backup system (hybridization) when solar radiation intensity is low
and when a quick response is needed. Fossil or renewable fuels can be used, but solar
PV is occasionally used.

2. SOLAR ENERGY RESOURCES: SUN CHARACTERISTICS
AND SOLAR RADIATION

The Sun was formed 4.6 billion years ago and is estimated to last 5 billion more. It is
the main source of energy for all processes in the Eartheatmosphere system, consti-
tuting more than 99.9% of this system. The main characteristics of the Sun are as
4
follows :
6
• It is a luminous gaseous star, with a diameter of 1.39 10 km (100 times that of
12
30
2
the Earth), surface area of 6.08 10 km ,and amassof 1.989 10 kg
(300,000 times that of the Earth); its density is more than 100 times that of water.
3
U. Pelay, L. Luo, Y. Fan, D. Stitou, M. Rood, Thermal energy storage systems for concentrated solar
power plants, Renew. Sustain. Energy Rev. 79 (2017) 82e100.
4
N. Armaroli, V. Balzani, Energy for a Sustainable World: From the Oil Age to a Sun-Powered Future,
Wiley-VCH, Weinheim, Germany, 2011.