An introduction to the manufacturing and science about the solar energy panels that are on your roof already, and the panels that you are considering to put on your roof, and how they could impact your return on investment.
Solar Energy Cells are made out of a semiconductor material, which is a special type of material that conducts electricity at certain conditions. In the case of solar energy cells, the condition is dependent on the different amounts of wavelength of light that it accepts, which it then converts into electricity. There are several types of materials that can be classified as semiconductors but the most common one used in the Photovoltaics and Solar Energy Panel Industry is Silicon. This is primarily because Silicon is the second most abundant element in the earths crust and because of the existing infrastructure developed by the Information Technology industry and their accumulated experience of using this material. To a lot of industry experts this means that, in the long run, silicon based solar energy panels should be the most affordable method of generating renewable electricity from the sun.
This leads me to my next point and probably the question you are thinking about. What types of Silicon Solar Energy Cells are out there?
There are several types of Solar Energy Cells but the general categories are:
1) Monocrystalline
Chemical Definition: This type of Silicon has an ordered crystal structure, with each atom ideally lying in a pre-ordained position and exhibits predictable and uniform behaviour.
What-that-means: This type of Silicon goes through several cycles of slow and energy intensive filtration and separation processes and thus is the most expensive type of silicon.
Interesting point: These cells are usually created in a circular shape or a ‘square-without-corners’. This is because, when they are grown from an ingot, the only way to create high purity crystal structures is to extruded the molten liquid and gravity does the rest with respect to creating a cylindrical block out of which the smaller cells are cut. Usually manufacturers will leave cells in a circular shape however due to advances in recycling, the cells are being chopped into squares-without-corners to maximize the packing density of the modules.
2) Multicrystalline/Polycrystalline
Chemical Definition: This type of Silicon contains several regions of crystalline Silicon kept together through covalent bonding and separated by ‘grain boundaries.’
What-that-means: This type of silicon goes through a lower number of cycles of the energy intensive filtration and separation processes that monocrystalline cells do and therefore are a less expensive material for manufacturers to use.
Interesting point: These cells are usually grown in a square shape. This is because the molten liquid in the (square) ingots does not to be extruded or go through another process to produce the big block of silicon out of which the little cells are cut. (Grain boundaries can have an interesting effect on efficiency and this shall be covered in a later article)
3) Amorphous
Chemical Definition: This type of Silicon has an even less regular arrangement of atoms, which result in dangling bonds and several gaps where recombination can take place.
What-that-means: This type of Silicon can be grown in any shape or size and can be produced, in theory, very cheaply.
Interesting point: These were the first type of solar energy cells that were used in the application of consumer products such as the watch, calculator and other non-critical outdoor applications and given their low cost they were adopted by other larger scale applications in the US.
Micro/Nanocrystalline or better known as Thin Film Solar Energy Panels are also one category of photovoltaic cells. This concept is an extension of the idea behind Amorphous Silicon however instead of using Silicon the industry in this case uses other elements, the most efficient of which is Gallium-Arsenide Thin-Film. These types of solar cells require less raw material which would imply that the cost of raw materials should be lower however, due to the high handling and processing costs of such thin cells, combined with the higher efficiency it makes it really difficult to judge whether its worth paying for. Nonetheless there is an application for these cells as well as can be seen in this link for the University of Michigan’s Solar Car: http://www.umsolar.com/
The next articles will take a further look at:
– What type of solar cells are the most efficient and why?
– How much power can I generate from my roof and how much will that cost me?
– Why are certain modules more expensive than others?
So stay tuned and post any other questions that you might have so I can include them as well.
Written by Prateek Chourdia
MEngSc – Photovoltaics and Solar Energy, UNSW
Solar Energy Analyst
Solar Choice
© 2010 Solar Choice Pty Ltd
Sources:
“Applied Photovoltaics” by Stuart R. Wenham et. al.
“Solar Cells” by Martin A. Green
