Orientation - how to install solar panels?

Only a small fraction of all sunlight actually reaches the surface of the earth

1. direct 2. absorption 3. reflection 4. indirect

The sunlight travels in a straight line from the sun to the earth. When it enters the earth's atmosphere part of the light is scattered and part of it reaches the surface in a straight line. Another part of the light is absorbed by the atmosphere. This scattered sunlight is what we call diffuse radiation or diffuse light. The sunlight that reaches the surface without being scattered or absorbed is of course direct radiation. Direct radiation is the most intense as everyone knows from sunbathing or working outdoors.

A solar panel produces electricity even when there is no direct sunlight. So even with cloudy skies a solar energy system will produce electricity (see How does it work). The best conditions, however, are bright sunlight and the solar panel facing towards the sun. To benefit most of the direct sunlight a solar panel has to be oriented as best as possible towards the sun. For places on the Northern Hemisphere this is south, for countries on the Southern Hemisphere this is north.

In practice, the solar panels should therefore be positioned at an angle to the horizontal plane (tilted). Near the equator the solar panel should be placed slightly tilted (almost horizontal) to allow rain to wash away the dust.

Solar Panel Energy Available at Various Light Conditions Relative to Full SunIntensity

Condition	% of full sun
Full sun – panel square to the sun	100%
Light Overcast	60-80%
Heavy Overcast	20-30%
Inside window, single pane, double strength glass, window and module square to the sun	91%
Inside window, double pane, double strength glass, window and module square to the sun	84%
Inside window, single pane, double strength glass, window and module at 45° angle to the sun	64%
Indoor office light – at desk top	0.4%
Indoor light – store lighting	1.3%
Indoor light – home	0.2%

A small deviation of these orientations has not a significant influence on the electricity production because during the day the sun moves along the sky from east to west.

Example

Percentages of annual yield for a PV system with a panel inclination of 45 degrees for several orientations, The Netherlands.

W	SW	S	SE	E
78%	94%	97%	94%	78%

The yield is maximum (100%) when the panels are tilted 36 degrees and oriented south. As can be seen the differences between south-west, south and south-east are small.

Information from http://www.mysolar.com and other sources were used, hardly edited by our engineers.

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