Solar Energy On Earth Surface

Among the most common devices used to capture solar energy and convert it to thermal energy are flat plate collectors which are used for solar heating applications.

Solar energy on earth surface. The earth receives 174 petawatts pw of incoming solar radiation at the upper atmosphere. If the extraterrestrial solar radiation is 1367 watts per square meter the value when the earth sun distance is 1 astronomical unit then the direct sunlight at earth s surface when the sun is at the zenith is about 1050 w m 2 but the total amount direct and indirect from the atmosphere hitting the ground is around 1120 w m 2. Solar energy is the most abundant energy source on the planet. The earth s surface radiates the net equivalent of 17 percent of the incoming solar energy in the form of thermal infrared.

It is measured on a surface perpendicular to the rays one astronomical unit au from the sun roughly the distance from the sun to the earth. Calculating solar energy to surface energy from sun to earth. Even in sunny parts of the world s temperate regions for instance a collector must have a surface. Approximately 30 is reflected back to space while the rest is absorbed by clouds oceans and land masses.

The remaining fraction 5 to 6 percent is absorbed by the atmosphere by greenhouse gas molecules. The solar constant i sc is the average radiation intensity falling on an imaginary surface perpendicular to the sun s rays and at the edge of the earth s atmosphere figure 2 1 the word constant is a little misleading since because of the earth s elliptical orbit the intensity of the solar radiation falling on the earth changes by about 7 between january 1 st when the earth. However the amount that directly escapes to space is only about 12 percent of incoming solar energy. The spectrum of solar light at the earth s surface is mostly spread across the visible and near infrared ranges with a small part in the near ultraviolet.

Solar irradiance is the power per unit area received from the sun in the form of electromagnetic radiation as reported in the wavelength range of the measuring instrument. At the earth s surface the energy density is reduced to approximately 1 000 w m2 for a surface perpendicular to the sun s rays at sea level on a clear day 1. Because the intensity of solar radiation at earth s surface is so low these collectors must be large in area. The solar constant includes all types of solar radiation other than neutrinos not just the visible light.

The sun is generally considered to produce a constant amount of power although there are small variances in the output energy depending on sunspot cycles with a surface intensity of expressed in units of power per unit area as the sun s rays spread into space this radiation becomes less and less intense as an inverse square law. Solar energy is harvested by capturing light for direct photovoltaic conversion into electricity or as thermal energy heat water heating space heating and other uses.