Energy Education Science and Technology 2007 Volume(issue) 18(2): 101-114
Solar energy potential assessment using GIS
T. V. Ramachandra
Centre for Ecological Sciences, Indian Institute of Science Centre for Application of Science and Technology to Rural Areas (ASTRA), Indian Institute of Science, Bangalore 560 012, India
Received 07 December 2006; accepted 15 December 2006
Abstract Renewable energy resources are those having a cycling time less than 100 years and are renewed by the nature and their supply exceeds the rate of consumption. Renewable energy systems use resources that are constantly replaced in nature and are usually less polluting. In order to tap the potential of ...view middle of the document...
The intensity of the sun's radiation (irradiance) at the top of the earth's atmosphere at the mean distance of the earth from the sun is roughly constant (solar constant) with an observed value of 1366 Watts/m2 ± 0.3%. However, on average, only about half of this energy reaches the earth's surface .
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T. V. Ramachandra / Energy Education Science & Technology
The total quantity of short wave radiant energy emitted by the suns disc as well as that scattered diffusively by the atmosphere and cloud, passing through a unit area in the horizontal in unit time is referred generally as global solar radiation. Monitoring the daily global solar radiation will help in assessing the total solar energy at any location considering diurnal and seasonal variations. The global solar radiation reaching the earth’s surface is made up of two components, direct and diffuse. The sum of the direct and diffuse components reaching a horizontal surface is global radiation. Direct radiation is the part, which travels unimpeded through space and the atmosphere to the surface; and diffuses radiation is the part scattered by atmospheric constituents such as molecules, aerosols, and clouds. In simple terms, direct radiation causes shadows, and diffuse is responsible for skylight . Approximately 30% is reflected back to space, and clouds, dust, and “greenhouse” gasses such as water vapor, carbon dioxide, and ozone absorb the remaining 20%. The annual global radiation in India varies from 1600 to 2200 kWh/sq.m which is comparable with radiation received in the tropical and sub-tropical regions. The equivalent energy potential is about 6,000 million GWh of energy per year . 1. 1. Characteristic of the solar radiation Solar radiation is made up of electro-magnetic waves (Es), which travels from the sun to the earth with the speed of light (c). Wavelength (λ) of the wave is related to the frequency (υ), and is given in Eq. 1. C = υλ (1)
The electro-magnetic waves of solar radiation (Es, cal/min) emitted into the space and its part intercepted by the earth (Ee, cal/min) is given by: Es = 4πro2Io Ee = 4πro2Io (2) (3)
where, ro, re, Io are the mean distance between sun and earth, the radius of the earth, and solar constant, respectively. The part of solar radiation intercepted by the earth depends mainly on the insolation of the earth’s outer atmosphere. 1. 2. Insolation at the outer atmosphere Insolation is the rate at which energy reaches the earth surface. It is the absorption of solar radiation by the earth surface . If the earth were represented as a sphere, then at the equator a horizontal surface at a point immediately under the sun would receive 1.36 kW/sq.m continuously. Horizontal surface on the same longitude but different latitude would receive...