Types of Solar Modules
Interested in going solar but unsure of how to pick the right solar panel for your home? The following article will explain the different types of solar modules along with best application practices to help you better determine the right fit for your system. We will start with the different types of solar panels on the market, look at their benefits and downsides, then look at some different scenarios that will help you see how certain types of solar panels may be more beneficial than others.
What is Silicon? (What are solar panels made of?)
Today 90% of the world’s photovoltaics today are based on some variation of silicon according to the National Renewable Energy Laboratory (NREL). In 2011, about 95% of all shipments by U.S. manufacturers to the residential sector were crystalline silicon solar panels. Silicon can take many forms and the main difference is the purity. In this case purity means how well aligned the silicon molecules are, which will allow the solar cell to better convert sunlight into energy. This is the PhotoElectric Effect. (Interested in learning more about the PhotoElectric Effect… click here.)
Monocrystalline
Monocrystalline silicon are easily recognizable by the diamond shape markings visible on the external part of the module. Monocrystalline cells are harvested from a single silicon ingot which are cylindrical in shape. The four sides are cut at an angle to optimize performance and this is what gives these panels their “signature look” (uniform, black shiny surface). These panels tend to have the highest efficiencies because they are made from the purest silicon. These panels also tend to have the highest power output per 1000/m2 which makes them more space efficient. These types of modules are also rated to perform better in lower light conditions than their polycrystalline counterparts.
Polycrystalline
Polycrystalline solar panels have a simpler manufacturing process compared to that of monocrystalline solar modules and this makes these modules less costly than their counterparts. Raw silicon is melted and poured into a square mold, which is cooled, then cut into the square wafers. Polycrystalline solar panels have a lower heat tolerance than monocrystalline solar panels, but the difference is so minor that most consumers do not take it into account. Cosmetically, these panels have a blueish color which easily distinguishes them from their monocrystalline counterparts. Both modules are usually available in black or clear frame.
So, what are the differences?
Monocrystalline solar panels tend to be more expensive, but are also slightly more space-efficient. If you had one polycrystalline and one monocrystalline solar panel, both roughly the same size (65” x 39”), the monocrystalline solar module would have a higher wattage output than the polycrystalline module by standard comparison. If they generate the same amount of electricity, the one made of monocrystalline silicon tends to take up less space.
You will generally need more polycrystalline modules to get the same wattage output for a surface area than with monocrystalline modules since they are not as space efficient. Though polycrystalline modules are less efficient, it does not mean that they perform any less, rather that you just need more of them.
People will readily notice the physical difference of the modules since the monocrystalline panels have a uniform black finish while the polycrystalline modules have a speckled blue tint.
Monocrystalline panels are generally 10-15% more expensive per watt than polycrystalline. However, warranties for either type are almost always the same (25 years).
Small Area Modules (SAM) vs Large Area Modules (LAM)
SAMs are typically classified as a 36 cell module that is 190 watts or less. These modules are manufactured with both poly or monocrystalline cells, though most are polycrystalline. SAM’s are often used in small off grid installations or used as a charging source for recreational vehicles and boats. The common SAM nominal voltage is 12 volts, however, they can be found in 24 and 48 volt depending on the application. The further the module is away from the load and/or battery, the higher the voltage needs to be. SAM production/manufacturing is more labor intensive therefore these modules are more expensive per watt than LAMs, which have a more automated “hands off” production process.
Though LAMs are generally found in residential/commercial installations, they are also used in off grid projects. LAMs can be 60 or 72 cells as well as poly or mono. The output range for 60 cell modules is 200-300 watts. 72 cell modules are normally 300+.
So what does efficiency have to do with anything?
The purity of a monocrystalline solar cells enable electrons to move more freely than the multicrystal sell make up of polycrystalline cells which results in greater efficiency. Monocrystalline cell efficiency typically peaks at 22%. Polycrystalline normally tops out at 18%. *see solar panel efficiency formula at end of article. Another advantage to monocrystalline panels is that they perform better in low light conditions and in higher temperatures than their polycrystalline counterparts.
The Bottom Line
If you have the space and exposure, polycrystalline panels are a cost effective solution when installation space isn’t limited, particularly if the installed in an area with excellent southern exposure. Monocrystalline are more expensive but can be a better solution when the available installation space is limited, and/or southern exposure isn’t optimal. While efficiency is influenced by the purity of the silicon, it is not always the primary concern. For most people, it is the trade-off between cost and space efficiency. If size is important, you should go for the highest rated power output for a particular physical size.
For those who want to take a more hands on approach, here is how you calculate module efficiency:
- Determine the surface area of the panel by multiplying the length by
the width. For example a SolarWorld 245W Mono panel is 1675 mm long
by 1001 mm wide or 1,676.67 square meters. The surface area is aperture
area of the solar panel, therefore, this does include the frame.
- Pull the nameplate rating of the panel from the datasheet. For
example if it is a 245 W panel, that is the nameplate rating at STC
- At STC the watts per meter squared (W/m2) is 1,000 W/m2 This is
the standard used to determine how many watts of power are produced in
a square meter on earth. (Note: Temperature is always a factor in the
output of a panel so STC assumes less than 25 degrees C.)
- Divide the nameplate rating by the square meters at 1000 W/m2 to
get the solar panel efficiency. In our example for the SW245 mono (245/
1.676.67)=14.61% efficiency
- Remember to look at the power tolerance as although the name plate
rating might be 245W, the power tolerance will tell you how many more or
less Watts a the STC the panel produce. In this example the SW245
Mono have a power tolerance of -3%/+3%.
The solar cell peak efficiency might be a few percentage points higher
when tested at STC. Those points of efficiency are lost in the movement of
energy from the cell to the output of the module.
Overall, we hope that the information above provides our readers with a deeper level of understanding of the different modules available on the market and helps the buyer determine the correct one for their needs.
