To calculate the sun position at a given place and time and thereby study the variation in power production in a solar photovoltaic panel with respect to the change in incidence angle.
Background and Introduction
Sun is considered as the prime source of energy on the planet earth because of the vast amount of energy that is freely made available. Solar energy being green, renewable source of energy, should be tried to get the maximum output from and used in different ways. The most common and easiest ways is using photovoltaic cells, which will directly convert solar energy to electricity.
Solar pv cell
A solar photovoltaic cell is an electronic device which produces direct current when sun light is incident on it. Photovoltaic materials like mono crystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and copper indium gallium selenide/sulphide are used in a solar cell. These cells are electrically connected together to make a solar photovoltaic module.
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Theory of operation
The cells work on the principle called photovoltaic effect. When the light beam hits the solar panel, the photons excite the electrons to a higher energy state and acts as the charge carriers for an electric current. There is an electric field in the panel structure which combined with the movement of the electrons causes an electric current.
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Relation with the incident light
Power produced by a solar cell is proportional to the power of the incident light and the angle at which the panel is kept to the incident light. When the Panel is kept perpendicular to the sunlight, power density on the panel is maximum. When the panel is aligned parallel to the sunlight power density is zero.
Necessity for tracking the sun
Throughout the day after the sunrise the sun moves in the sky from east to west. So the direction of the incident light on the panel also changes. In order to have maximum efficiency, the panel has to be kept perpendicular to the incident light always.
Finding the sun position
In order to align the panel perpendicular to the sunlight always, we first need to know the suns position at a given place and time.
Sun position in the sky is decided by the following factors
- Sun Elevation
- Sun Azimuth
Solar Elevation or Solar Altitude refers to the angle the sunlight makes with the horizontal. When the sun is directly above our head the elevation is 90 degree. When the sun is on the horizon during sunset or sunrise, the elevation is 0 degrees. Elevation is decided by the following parameters
- Latitude of the place.
- Declination of the earth.
- Time and date.
Latitude is marked from 0 degree to 90 degree. It’s generally marked from the equator to the north south axis.
Declination is the angle which the equatorial plane of the earth makes with the line joining the centre of the earth and the sun. Declination of the earth varies with the date of the year.
Where d is the date.
So we have,
Zenith is always marked on the vertical plane. It refers to the angle the sunlight makes with the vertical. When the sun is directly above our head the zenith is 0 degree. When the sun is on the horizon during sunset or sunrise, the zenith is 90 degrees. Both the Elevation and the Zenith are always marked on the vertical plane
Azimuth refers to the angle the north south line makes with the line drawn from the point of reference and the suns projection on the horizontal plane. Azimuth is always marked on the horizontal plane. Azimuth of the sun is depending on the declination, latitude of the point of reference, Solar Elevation, time of reference and latitude of the point of reference.
- is the solar elevation angle.
- is the Declination of the earth.
- Ø is the latitude of the point of reference.
- HRA is the hour angle(The angle which the hour hand makes with horizontal plane)
So we can pin point the position of sun in the sky if we have the Solar Elevation (α), Solar Azimuth (Α).
The panel is placed at an angle calculated using the above equations, if the user picks automatic tracking and the panel moves to the user selected angle if the tracking mode is manual.