There are of course many different brands of solar energy panels out there on the market. But there are actually only three different types of solar panels, classified by the materials used to make the solar cells they contain and the manufacturing processes involved in making those cells – monocrystalline silicon, polycrystalline silicon, and thin-film (the latter category features three subtypes that are currently available: amorphous silicon, cadmium telluride, and copper indium gallium selenide).
Naturally, each type has its strengths and weaknesses, and the potential solar panel consumer will want to do some careful research before making a final decision about which type to purchase.
Monocrystalline Silicon Solar Cells
Silicon has been the material of choice in solar photovoltaics for more than half a century. But silicon will not function very effectively as a solar cell semiconductor unless it has been purified first, meaning that its molecules must be brought into unity and alignment so electrons can pass through efficiently without excessive resistance. There are multiple methods of purifying silicon so that it will be acceptable for use in the production of semiconductors, and if a monocrystalline structure is desired, the purity level attained must be very high indeed.
But simply removing stray impurities from silicon is not enough to make it appropriate for use in monocrystalline solar cells. To proceed further, the freshly purified silicon must be melted down, and then a rod with a single silicon crystal attached will be dipped into the molten substance and rotated back out in an upward direction. The original crystal functions as a seed, and as the molten silicon merges with the seed and crystallizes around it, a perfectly aligned and harmonized macro-crystal will be formed in the shape of a cylinder. Because the cylinder is essentially the equivalent of one crystallized molecule, electrons can pass through it with minimal resistance, making it a semiconductor of extraordinarily high quality.
Once created, the crystallized silicon cylinder will be shaved off repeatedly until only a thin silicon wafer remains. As per the usual process, solar panels can be produced by enclosing a large number of monocrystalline wafers inside rectangular panes of glass framed with aluminum, creating a highly-effective energy device that will be able to capture an impressive amount of the sun’s daily radiation.
Monocrystalline Silicon: Advantages And Disadvantages
- Monocrystalline silicon solar cells are more efficient than their competitors, with efficiency ratios of 15 to 20 percent (this number represents the amount of solar radiation collected that is actually converted into usable electricity).
- Since their higher efficiency means you can get by with fewer of them, monocrystalline solar panels require less space than the other two alternatives.
- These solar panels have a longer lifespan than any other type, and most panel manufacturers will issue twenty-five-year warranties for them at the time of purchase.
- In low-light conditions, monocrystalline silicon solar cells will outperform similarly rated polycrystalline silicon solar cells.
- In high heat conditions, monocrystalline silicon panels are more effective than those made from polycrystalline silicon cells.
- The complicated process of crystallization and the amount of waste that is generated when the cylinders are shaved down to size pushes up the price of monocrystalline solar panels and makes them the most expensive available on the market.
- While monocrystalline silicon outperforms polycrystalline silicon in hot weather, it still does not perform particularly well when the mercury rises to Death Valley-in-July or Deep South-in-August levels.
- If one of these panels is in the shade or is covered up by some other type of obstruction, the full solar array circuit could conceivably malfunction and shut down (micro-inverters that change DC to AC on each panel separately can eliminate this risk).
Polycrystalline Silicon Solar Cells
Polycrystalline silicon cells arrived on the scene in 1981 and have been marketed as a less-expensive alternative to monocrystalline. Silicon of a lower grade than that used in the monocrystalline synthesizing process is melted and poured into square molds, and when the mold has cooled, a solid silicon ingot will be created that can be removed and sliced into multiple thin wafers.
Polycrystalline silicon cells do not have the singular, unified nature of the monocrystalline solar cell, and as a result, they have more resistance to electron flow than their more fully purified cousins. Nevertheless, polycrystalline silicon is able to capture and harvest solar energy quite effectively, notwithstanding its less stringent manufacturing requirements.
If you have ever seen a glossy black solar panel with circular cells on the interior, you were no doubt looking at a monocrystalline silicon solar panel, while the blue ones with the square cells would be the polycrystalline silicon version.
Polycrystalline Silicon: Advantages And Disadvantages
- Thanks to the simplicity of the manufacturing techniques involved in their creation, polycrystalline silicon solar cells are less costly to purchase than monocrystalline.
- Because they are cut into squares instead of circles, polycrystalline silicon cells can be packed in more densely with less wasted space, and the greater number of cells on a polycrystalline solar panel in comparison to its cousin helps to make up for some of the efficiency differences.
- Polycrystalline silicon solar panels also have a long lifespan, and are generally guaranteed to last for twenty-five years just like the monocrystalline silicon version.
- Polycrystalline silicon solar cells have a lower efficiency rating than monocrystalline, coming in at 13 to 16 percent (which admittedly is still good in comparison to thin-film solar cells, which we will be looking at shortly).
- Polycrystalline silicon solar panels struggle to function in high heat even more so than the monocrystalline silicon variety.
- A polycrystalline silicon array will need to be larger and will cover more space than a monocrystalline silicon set-up, and of course it will therefore require more maintenance, will be more likely to need repairs, and will have more solar energy infrastructure costs.
- Some people complain that the blue polycrystalline silicon solar panel is not particularly attractive, in part because polycrystalline cells are not always a uniform blue color.
Thin-Film Solar Cells
As recently as 2005, crystalline silicon controlled 95 percent of the U.S. market for solar panels. But that percentage has now dwindled to just 75 percent, and it is thin film that has been making all the in-roads. The thin filmmaking process begins with the use of a substrate upon which amorphous silicon, cadmium telluride, or copper indium gallium selenide compounds are layered using a technique called chemical vapor deposition. These layers of photovoltaic materials are very thin indeed, ranging from nanometers to a few micrometers in thickness. Using a substrate to support solar cell wafers simplifies the process of manufacture by a good bit, eliminating the need for some of the precise detailing work that is needed when crystalline silicon is being formed and turned into solar cells.
Because the synthesizing process is so simple, convenient, and requires the least amount of photovoltaic raw material, most of the research-and-development currently taking place in solar cells is centered around the thin-film option. At this time thin film is still very much the new kid on the block, but it is rapidly growing into adolescence and can be expected to reach full technological maturity by perhaps as soon as the year 2020.
Thin-Film: Advantages and Disadvantages
- Ease of manufacture means cheapness of price, and thin film is likely to only get cheaper as time goes along.
- Thin film can rise to challenges that crystalline silicon cells cannot – high heat, shading, snow, a bear taking a nap on the panels; you name it, thin-film can handle it smoothly and without disruption of service.
- The substrates used in the process of manufacture are mostly cheap and easy to find, i.e. glass, metal, and plastic.
- Amorphous silicon, which is the most commonly used thin film photovoltaic material, can absorb forty times more solar radiation than monocrystalline silicon, making up for the fact that it operates less efficiently as a semiconductor.
- Thin-film solar cells backed by the proper substrate can actually be manufactured in flexible forms, and there is little doubt that flexible solar panels that can be shaped and bent for custom fit will open up possibilities in solar energy that never existed before.
- One monocrystalline silicon solar panel can produce as much electricity as four thin-film panels because the relatively impure materials used in thin-film cells impede smooth electron flow.
- Impurity equals inefficiency, and the efficiency rates for thin-film solar cells range from 6 to 8 percent for amorphous silicon to 9 to 11 percent for cadmium telluride to 10 to 12 percent for copper indium gallium selenide.
- Needless to say, you will need a lot more solar panels to provide electricity for your home if you go with thin film than if you choose crystalline silicon, since thin film’s space efficiency leaves a lot to be desired.
- The costs for cables, supports, and other types of infrastructure equipment will be much greater with thin film because of how many panels you will need to install to get the job done.
- Thin-film solar panels break down much faster, which is why their warranties will come nowhere near twenty-five years.
- Thin film is making progress, but most of it is presently being used on commercial-scale projects because of the space requirements. At the present time, thin film has only managed to capture about 5 percent of the residential market.
So Which Type Of Solar Panel Should You Choose?
And now comes the $64,000 question – monocrystalline, polycrystalline, or thin film?
While thin film might be the future, at the present time this technology has probably not developed far enough to be a practical home option, except for those who have few (if any) limitations to their budgets.
As for the polycrystalline/monocrystalline choice, at this stage it may be more a question of what your power demands are, what kind of space you have available for your solar panels, and of course how much money you have to spend that will help you make a final decision about which way to go once you have made up your mind to go the solar route. Monocrystalline silicon is more efficient, but you may find that the other options are more in your price range.
So there is no clear answer as to what type of solar panel should be purchased by an off-the-gridder looking to make the move to solar. A lot of research will be necessary before a final choice can be made, but it is wise to have at least some idea about the differences between the three types of panels before you actually start shopping.
One final thing that should always be kept in mind is that solar energy is a rapidly evolving field, and there may be new and exciting options available in a year or in two years that are not available right now. This may be especially true with thin-film solar panels, because that is where the most intensive research and development is currently going on. So just because a particular solar set-up seems right today does not mean it will still be your best choice tomorrow.
So stay tuned…
©2012 Off the Grid News