Definition of Insolation
The amount of solar radiation received by the earth’s surface is called insolation. Only two billionths of solar radiation are received by the earth and the rest of which goes to the outer surface. 30 percent of energy is reflected back by the atmosphere to outer space and 70% travels through the earth’s atmosphere. Out of this 70 percent radiation, some fraction reaches to earth surface and the rest is absorbed by the atmosphere. Some fraction of the radiation falls on earth surface reflected back to the atmosphere and the rest is absorbed by earth surface and various matters on the earth. The wavelength of radiation reflected by the earth’s surface is greater than direct radiation from the sun.
The amount of insolation is measured in two units, one is kilowatt Hours per square meter that represents the amount of solar energy received by one-meter square area per day. The other unit is kilowatt per square meter, which tells how much power hits in one square meter area per year.
Factors influencing Insolation
The amount of solar radiation that hits on the earth surface, i.e, insolation is influenced by some factors, they are:
1. Angle of solar radiation fall
2. Duration of sunshine
3. Transparency of atmosphere
1. The angle of solar radiation fall
If we consider earth as a perfect circle, then it will be easy to draw a tangent to this circle. The angle created by sunlight with this tangent at any point is called the angle of radiation. The equatorial region gets the maximum insolation as the angle of insolation is 90 degrees, sunlight falls directly from overhead, that’s why it requires a short distance to travel to reach the earth’s surface. As we go to polar regions from equatorial region, the angle of inclination of sunlight increases. So it has to travel more distance through atmosphere, resulting in more absorption of sunlight in the atmosphere.
2. Duration of sunshine
Earth gets more sunlight when the day is long, conversely, earth gets less solar radiation when day time is short. So, the amount of insolation is more in summer than winter. Days are maximum in the equatorial region compared to the polar regions, so insolation is also maximum in equatorial region.
3. Transparency in atmosphere
The atmosphere is the combination of various gas particles, dust and water vapor. These particles absorb sunlight. The more the atmosphere fills with these particles, the less the transparency of atmosphere will be. As absorption of solar radiation is less in a transparent environment, so to get maximum insolation environment must be clear and transparent.
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