SOLAR PANELS

Different Cell Types

There are three types of solar panels available:monocrystalline, polycrystalline and amorphous. To produce a monocrystalline silicon cell, absolute pure semi conducting material is necessary. Monocrystalline rods are extracted from melted silicon and sawn into incredibly thin plates. Panels constructed this way are found to provide the highest efficiency, however these are more expensive to produce than other types.

The production of polycrystalline cells is more cost-efficient. In this process, liquid silicon is poured into blocks that are then sawed into plates. During hardening of the material, crystal structures of varying sizes are formed. At the borders of these crystals, defects begin to emerge. As a result of this crystal defect, the solar cell is less efficient.

When silicon film is deposited on glass or another material, it is an amorphous or thin layer cell. The layer thickness amounts to less than 1µm (a human hair is 50µm-100µm), therefore making the production costs lower due to the low material costs. However, the efficiency of amorphous cells is much lower that that of the other two cell types. Because of this they are mainly used in low power equipment such as calculators. [http://www.solarserver.de/wissen/photovoltaik-e.html]

How a Solar Cell Works

Billions of photons (energy packages) stream down from the sun to the earth. When photons of sunlight hit a solar panel, some are absorbed into the solar cells, where their energy knocks loose some of the modified silicon electrons. The electrons are pushed by the internal electrostatic field to the front of the cell. They lose some of their energy as they are pushed through the field and end up with about half a volt of potential energy. This is the “voltage” of the solar cell. Half a volt of power is not much, so a typical solar module consists of many solar cells front to back in series.

Cells connected in a series have a higher voltage while those connected in parallel produce more electric current. The interconnected cells are embedded in transparent ethyl-vinyl-acetate, fitted with and aluminum or stainless steel frame and covered with transparent glass on the front side. Electrons flow along the surface of a solar cell and into thin silver gridlines that cover the entire cell surface. In a good conductor, like silicon, the electric current flows easily into flat tin-coated copper ribbons soldered to the front of the cell and into the back of the next solar cell.[http://www.solarserver.de/wissen/photovoltaik-e.html]

When it is a cloudy day and the intensity of the photon is lower, the current flowing from the cells and entire array diminishes. When the cloud passes away and full sunlight reappears, the flow of electric current returns back to its full capacity. As the sun sets slowly in the evening, the current also reduces, until darkness where there is no electric current flow from the solar array. The most common method for still providing electricity during these periods is to use storage batteries. However, it is now possible to use the mains electricity grid as a ‘battery’ for a solar power system.

The working life of a solar panel should be in excess of 20 years. They require virtually no maintenance, but dust or grime on the front of solar panels will substantially reduce the output, so they should be cleaned periodically. Photovoltaic panels also suffer from decreased power output when they heat up, so when it is extremely hot they may not power efficiently. [http://www.ata.org.au/basics/bassolar.htm]