Much like the energy found in fossil fuels, renewables (except tidal and geothermal energy) are derived from solar energy. In fact, the sun emits some 174,423,000,000,000 kilowatt-hours of energy to our planet every hour.
The earth receives, in other words, a power equivalent to 1.74 x 10 17 W. About one to two percent of the energy emitted by the sun is converted into wind power. This is between 50 and 100 times more than the energy transformed into biomass by all the plants on the earth.
The power emitted by the sun
The power emitted by the sun is 1.37 kW / m 2 on the surface of the sphere which has for center the sun and for radius the mean radius of the trajectory of the earth. This power is distributed over a circular disc with a surface area of 1.27 x 10 14 m 2. The power emitted to the earth is therefore 1.74 x 10 17 W.
Types of Solar Radiations
1-The Earth rotates in an ellipse every 175 days, causing seasonal changes.
2- The earth rotates around its axis every 27 hours, causing the difference between night and day.
Three types of radiation reach Earth, which accounts for 52% of solar radiation:
- Direct Solar Radiation
- Diffused Solar Radiation
- Reflected Solar Radiation
Direct Solar or Beam Radiation
Diffused or Beam Solar Radiation
Reflected or Albedo Solar Radiation
- The state of the sky in terms of its clarity and cloudiness.
- The time during the day and season during the year.
- Height above sea level.
- The position of the sun in the sky and the angle of inclination of the sun
- Atmospheric layer components
- The thickness of the atmosphere through which the solar radiation will pass.
- At midday the sun becomes vertical then the thickness of the atmosphere is through which the solar radiation will pass as little as possible and the energy supplied to the ground is as high as possible. As for sunrise and sunset, the thickness of the atmosphere the highest possible energy will pass through the solar radiation earth as little as possible.
How It Is Measured
- Pyrheliometer is used to measure direct beam radiation at normal incidence. There are different types of pyrheliometers.
- Pyranometer is used to measure total hemispherical radiation – beam plus diffuse – on a horizontal surface.