Regional and Seasonal variations in the solar power

- Solar constant
- Earth’s Energy Budget
- The effect of latitude on incoming solar radiation
- Earth’s orbit and the seasons
- Latitude – time distribution of incoming solar radiation
- Sources

Solar constant
The amount of power that arrives from the sun is measured by the solar constant. It is properly defined as the amount of solar energy that falls per second on an area of 1m2 above the Earth’s atmosphere that is at right angles to the Sun’s rays. Its average value is about 1400 Wm-2

Earth’s Energy Budget
This is not the same as the power that arrives on 1 m2 of the Earth’s surface. Scattering and absorption in the atmosphere results in less than half of this arrives at the Earth’s surface.
Diagram explaining how the incoming solar energy disperses as the sunlight gets into the Earth’s atmosphere


The diagram above explains that not all incoming solar energy is reaching the Earth’s surface. Approximately 6% of incoming solar energy is reflected by atmosphere, 20% reflected by clouds and 4% reflected from earth’s surface. Furthermore, approximately 16% of incoming solar energy is absorbed by atmosphere and 3% absorbed by clouds. This results in only 51% of original incoming solar energy to reach the Earth’s surface. This explains how the
amount of solar energy that arrives to the Earth’s surface depends greatly on the weather conditions.

The effect of latitude on incoming solar radiation
Different parts of the Earth’s surface (regions at different latitude) will receive different amounts of solar radiation.
Diagram explaining how the latitude

Average input of solar radiation to the earth’s surface directly related to the latitude. Heating is most intense when the sun is directly overhead, so that incoming solar radiation strikes perpendicular to the earth’s surface. The higher latitudes are cooler than the tropics because the same quantity of solar radiation is dispersed over a greater surface area (a as opposed to a’) and passed through a.

The effect of seasons on incoming solar radiation
The amount of solar radiation received by Earth’s surface will also vary with the seasons since this will affect how spreads out the rays have become.
Diagram explaining how the amount of the solar
radiation and intensity varies with seasons

During summer time, the Northern part of the Earth receives more intense sunlight since the Northern parts of the Earth tilts toward to the sun. Comparing to intensity of sunlight that the Southern part receives, the Northern part receives more intense sunlight than that of the Southern part because the same quantity of solar radiation is dispersed over lesser surface area. This applies oppositely when the season changes to winter. Notice here that regions lay in equator constantly receives solar radiation and intensity over time. This proves that the amount of solar radiation received by Earth’s surface varies with the seasons.

Latitude – time distribution of incoming solar radiation
Diagram explaining how the incoming solar radiation
varies with latitude and time of year

At any particular location the solar radiation flux is determined by the time of the day, the season, and the geographical latitude. Furthermore, weather provides an unpredictable element. Under clear skies the radiant energy will be mostly direct, with only about 15% being diffuse, while under overcast conditions, obviously 100% of the radiant energy is diffuse. Australia is particularly lucky, with its solar radiant energy flux being more direct and constant than most countries, with peak maxima rising as high as 1.4 kW m-2. Notice here that while countries on the Northern or the Southern side of the Earth has sinuous period in receiving solar radiations due to seasonal and regional variations, the countries that lie on the equator receive consistent solar radiations throughout the year, generating proficient capacity.

“Earth’s Energy Budget.” EDRO. Nasa. 30 Mar. 2009

"Energy flux from the sun." The Earth's orbit and the seasons. 1 Apr. 2009

Kushnir, Yochanan. "Solar Radiation and the Earth's Energy Balance."
The Earth Radiation Budget 1 Apr. 2009. <>.

Richard Walding, Greg Rapkins, and Glenn Rossiter. New Century Senior Physics. South

Melbourne: Australia, 1999.

“Solar constant.” Earth’s season. MarineBio Inc. 1 Apr. 2009


"Solar energy." Wikipedia, the free encyclopedia. 03 Apr. 2009