A solar panel is a set of solar cells that convert light energy into electric energy. A number of solar panels, a battery, interconnection wiring and an inverter constitute a large photovoltaic system that generates electricity for residential and commercial applications. Silicon material is of prime importance in manufacturing solar panels. Most of the solar panels are monocrystalline or polycrystalline modules. The efficiency of the solar panels depends on their construction. The panels produce electricity within the frequency range of light incident on the panels.
Unlike other energy sources, solar panels do not pollute the environment while generating electricity apart from the pollution associated with the production and transportation of a solar cell. In addition, solar panel installations are maintenance-free, and have prolonged service life and silent operation. They require little maintenance, have no moving parts and can be operated efficiently. In spite of the high initial cost, solar panel systems are now being increasingly used to generate electricity in remote villages for electrification, irrigation and to pump water as well.
Materials Required for Solar Panel Manufacture
The basic raw material of a solar panel is pure silicon. However, the outer frame enclosing an array of solar cells in each solar panel is made of glass. The glass must be highly transparent to allow the sunlight to penetrate the frame. Moreover, for maintenance and safety purpose, the glass used in the panels should not be brittle.
Solar panels constitute two forms of silicon - crystalline and amorphous. Crystalline silicon cut and made into disks of 1 cm thickness is polished to act as a material for absorbing light. Solar panels also employ cooling materials to prevent damages caused by overheating. On the other hand, panels made of amorphous silicon can be continuously rolled and made into extremely thin silicon chips that can absorb different parts of the solar spectrum. Amorphous silicon is also less susceptible to damage during installation and transportation when compared to the crystalline form.
The solar module consists of a silicon semiconductor covered by a protective material in a metal frame. The protective material is provided with an encapsulant of transparent butyryl plastic or silicon rubber attached around the cells. The cells are then embedded in ethylene vinyl acetate. The back surface of the module is coated with a polyester film. The electronic components are made up of copper.
Image Credits: leichhardt.nsw.gov.au
Steps in Making a Solar Panel
The steps involved in fabricating a conventional polycrystalline silicon panel are as follows:
- To start with, very pure semiconductor-grade polysilicon is obtained from quartz in an electric arc furnace. With the application of carbon arc, molten polysilicon and carbon dioxide are obtained.
- The polysilicon thus obtained is heated to melting temperature and then added with traces of boron for forming a P-type semiconductor material.
- An ingot or silicon block is formed by either using a seed crystal extracted from the molten polysilicon or by casting the molten polysilicon in a block.
- The ingots are sliced using wire saws to obtain separate wafers, which are then subjected to a surface etching process. Solar cells usually employ hexagonal or rectangular wafers as they can be perfectly fitted together.
- The wafers are introduced in to a phosphorus diffusion furnace once they are cleaned to form a thin N-type semiconductor layer that covers the outer surface of the cell.
- The top part of the cell is then applied with an anti-reflective coating for reducing the loss of sunlight and provided with thin electrical contacts for connecting a solar cell to another and to a receiver.
- The back surface of each cell is deposited with an aluminized conductive material by displacing the diffused phosphorus layer in order to restore the P-type properties of the surface.
- Each cell thus formed is then tested, sorted depending on the current output and connected to other cells to form a solar panel.
Lifespan of Solar Panels
Solar panels are the most popular way of using the sun's energy to generate electricity for household and commercial applications. Most of the commercially available solar panels have a life expectancy of at least 20 years. The warranty given by the manufacturers for the first 10 years is more than 90% and over 80% for the second 10 years. However, with proper maintenance, solar panels can actually last nearly 40 years. Some solar panels are capable of giving 80% power output even after 40 years.
Researchers at the Centre for Alternative Technology in the UK, can determine the life expectancy of solar panels by installing 180 panels with an estimated peak output of 75W in 1997. When they again tested the panels in 2010, it was found that the panels had an output capacity of 68.5W, which is just 9% decrease over 13 years. Hence they concluded that even though panels experience certain physical damages, the effect of this on their performance was very limited. This suggests that the solar panels are capable of producing electricity for 30 years or more.
How to make Solar Panels - Run Time 5:11mins
Sources and Further Reading