PTUK Course (1): Solar Energy Systems (renewable energy)

The Sun is the star at the center of the Solar System.

It is a nearly perfect sphere of hot plasma. All of the bodies in the solar system revolve around it.

Earth makes a complete revolution around the sun every 365.25 days (one year). However, Earth's orbit is not a perfect circle; it is shaped more like an oval, or an ellipse. Over the course of a year, Earth moves sometimes closer to the sun and sometimes farther away from the sun. Earth's closest approach to the sun, called perihelion, comes in early January and is about 146 million km. The farthest from the sun Earth gets is called aphelion. It comes in early July and is about 152 million km.\

The Sun:                                                                                                                                                                                                                                                                                                                                                                                                               

    Sun every second.

The nuclear reactions are the reactions that are producing this energy

Four hydrogen atoms are changed into Helium atoms and energy is released.

4H  to        He + energy (Nuclear reaction)

The Sun converts 564 million tons of hydrogen into 560 million tons of helium every second. That means that every second 4 million tons of hydrogen is turned into energy

Ps is the emitted power from the sun surface.

Ps = σ * (Ts)4 * As = σ * (Ts)4 * Π * (Ds)2

σ is the Stefan Boltzman Constant = 5.67 * 10 -8 W/(m2K4)

Ds = 1.4 * 106 km

Ps = 3.8 *1023 kW.

Gn = Ps / (4 * Π * (rSE)2) = 1324 W/m2 ----- Solar Constant (calculated Value)

Gn measured 1353 W/m2

DSE = 1.5 * 1011(1 + 0.017 sin (360 (N-93)/365)) m

Gn = 1353 (1 + 0.34 cos ((360*N)/365)) W/m2

Extraterrestrial solar radiation (Outside atmosphere)

The Sun Radiation

Solar radiation is usually measured on horizontal surfaces that are free from obstacles. Global, beam (direct) and diffuse are solar quantities that may be measured on horizontal surfaces, but the solar quantity that is mostly measured is the global radiation.

The global radiation measured on horizontal surface (G_H) comprises of two components: beam (direct) component (G_b) and the diffused component (G_d)

       G_H=G_bn+G_d  

       where G_bn is the normal component of the beam radiation part, and is calculated using the following formula

        G_bn=G_b∗sin⁡α

where α  is the solar altitude angle that describes the angle between the horizon and the line to the sun (it is the complement of the zenith angle which is the angle between the vertical and the line to the sun).

This angle, alongside other angles that describe the position of the sun relative to a certain plane and orientation are shown in the figure below: