Which type of solar panel is best: monocrystalline or polycrystalline?
Choosing a solar panel can be confusing, and one of the common decisions is between mono and poly.
When it comes to buying solar panels for your home, there isn’t a lot that obviously differentiates one solar panel from other.
If you buy a car, there’s dozens, if not hundreds of different features, styles, and add-on options that you can take into account. But with a solar panel, there’s really only a handful of characteristics that make one product different from another. One of these is the type of material the individual solar cells are made of. Related to this, two terms you’ll come across are polycrystalline and monocrystalline, or simply poly and mono.
The vast majority of solar panels used in the residential market are made from crystalline silicon, which will be either polycrystalline or monocrystalline. These refer to how the silicon is formed.
Crystalline silicon explained
Silicon is the 14th element on the periodic table, and is the main ingredient in solar panels. The silicon for both mono and poly panels is crystalline silicon (meaning that the silicon atoms join together in a regular crystal lattice), but the manufacturing process differs between the two.
To make polycrystalline silicon, smaller chunks of silicon crystals are formed into larger ingots, which are then sliced into thin wafers to form solar cells.
Monocrystalline silicon, on the other hand, is made from a single large crystal. Growing a crystal large enough for solar cells involves a more difficult and expensive manufacturing process that uses higher purity silicon.
The end result is that monocrystalline cells are more efficient, generating more electricity with the same amount of sunlight compared to polycrystalline, but because the manufacturing process is more difficult, monocrystalline is more expensive.
Main differences between polycrystalline and monocrystalline
Of the solar panel characteristics that are important to a consumer, here are the three factors to take into account when deciding between mono and poly solar panels.
Monocrystalline looks better (most people think)
This is probably the most significant factor for most homeowners. While research has shown that on average solar panels will add significant value to your home, it’s certainly possible that you might encounter a potential home buyer who doesn’t like the look of solar panels on your roof.
Whether this matters to your situation will depend on how visible the panels are, especially from the street. If you have a situation where the panels are highly visible, the financial effect of curb appeal will probably be much, much more important than any relatively minor difference in price or efficiency between poly and mono panels.
Polycrystalline solar cells, which are made from small silicon crystals that are amalgamated into a large block, have a blueish, flakey appearance (the flakes are due to the individual smaller crystals). Monocrystalline cells are cut from a single large silicon crystal, and have a smooth, dark appearance.
Many people prefer the look of a solar panel that is completely dark from edge to edge. Keep in mind that the appearance of the panel is not just due to the type of silicon used, but also the color of the backsheet (which affects the color between the cells) and the color of the frame.
You can see the effect of the backsheet with the LG panels shown below. Both panels use dark monocrystalline cells, but one uses a white backsheet while the other uses black:
You can learn more about how to choose atttractive solar panels in our article about solar shingles, which goes in depth into both solar shingles and conventional solar panels.
Monocrystalline is more efficient
Monocrystalline silicon uses higher purity silicon and doesn’t contain crystal grain boundaries like polycrystalline silicon does. The result is a cell that provides less resistence to the movement of electrons, increasing the overall efficiency of the panel by up to a couple percent.
As a shopper, you’ll actually encounter few cases where the choice between two panels only comes down to a choice between mono and poly. In the quest for high efficiency, manufacturers will usually employ multiple technologies and processes to improve efficiency.
This means that a manufacturer might offer a lower cost polycrystalline solar panel, but use monocrystalline silicon and also other technologies like half-cut cells, heterojunction cells, or PERC cells in order to achieve the highest efficiency possible.
One of the few cases where you can find a 1:1 choice between mono and poly panels is with Yingli Solar. Their Multi 60 Cell panel has an overall efficiency of 18.0%, while their Mono 60 Cell panel boasts an efficiency of 19.8%. In all other respects, these Yingli panels are the same.
That’s nearly an overall increase of 2%. That’s a pretty good rule of thumb you can apply to other manufacturers but, again, keep in mind that premium monocrystalline solar panels often add other technologies to raise the efficiency even further.
Monocrystalline usually costs more
Using the Yingli panels again as an example, the 1.8% better efficiency of the mono panel translates to a 10% increase in relative efficiency. This means you’ll get 10% more electricity by choosing the monocrystalline panel over the polycrystalline.
Is the mono panel less than 10% more expensive than the poly panel? If so, it’s a good deal. But if you’re paying much more than that - and you often will - going with the lower efficiency poly panel might be the better financial move.
Keep in mind that there are cases where it makes sense to spend more to get higher efficiency panels. You might have limited roof space, and need to get as much production as possible with fewer panels.
Also, the cost of the panels is only one part of the overall system costs. More panels means more racking, and sometimes higher inverter costs. If you use power optimizers or microinverters, each panel is paired with its own inverter component. This means that using lower efficiency panels, even if they cost less per watt, might end up increasing your overall system costs more than if you chose monocrystalline because using more panels raises the cost of racking, inverters, and installation labor.
It’s also important to know that the price premium of monocrystalline panels isn’t as great as it used to be. Improvements in manufacturing and increased demand has lowered the cost of mono panels.
Finally, a big part of the price you pay is dictated by the price that your installer is able to get from their suppliers. Installers can reduce their solar panel costs through volume buying, supplier partnerships, and other methods. This means that the price for a solar panel you get through an installer will often be quite a bit lower than the retail price for a panel you find on the internet.
Because of this, you shouldn’t be surprised if you find a mono panel that’s actually cheaper than a comparable poly panel.
Differences to ignore
There are a couple characteristics of solar panels where the difference between mono and poly is debatable or too small to matter to the homeowner.
Temperature coefficient differences are minimal
A solar panel generates less electricity when it gets hot. This properly of solar panels is called its Temperature Coefficient, and you’ll find it listed on the published datasheet for any panel.
Temperature coefficient is listed as a negative number, indicating that efficiency drops by a certain percentage as the temperature increases. This means that a number closer to zero is better.
In theory, a monocrystalline solar panel will have a better temperature coefficient than a polycrystalline one, but the difference will be small: perhaps around 0.01%.
Looking at the Yingli panels again, there’s no published difference in temperature coefficient between their Mono 60 and Multi 60 panels. They both have the same power temperature coefficient of -0.39%/°C.
Longevity isn’t practically affected
In theory, monocrystalline silicon is manufactured to a higher standard and will last longer than polycrystalline.
However, in practice, solar panels don’t fail because of the silicon, but for other reasons. The number one reason is cracked glass, followed by other reasons such as damaged seals that allow moisture to creep in, potential induced degradation, and hot spots. Failure of the silicon itself isn’t really an issue.
If you want to buy solar panels that last as long as possible, focus on getting solar panels with the longest product warranty. Solar panel warranties come in two parts: a product warranty that covers parts and manufacturing, and a power warranty that guarantees against power output loss. Panels that are manufactured to a higher standard will tend to come with a longer product warranty - as much as 25 years, versus 10 years for cheap panels.
Choosing between monocrystalline and polycrystalline: the bottom line
There are some real differences between monocrystalline and polycrystalline solar panels. Most discussions about mono vs poly usually center on performance and the improved efficiency of monocrystalline, which might give you an absolute efficiency improvement of 2% on your system.
If you’re a utility company running a large solar farm with thousands of panels, that kind of difference may end up having a large impact on the financial bottom line. But a home solar system might have a couple dozen panels at most, with the total system cost difference between mono and poly being around a few hundred dollars.
That’s not a huge difference for a home improvement project that could last for 25 years or more. With a small home solar system, an efficiency difference of one or two percent doesn’t matter that much in the grand scheme of things. Instead, the biggest ROI impact will probably have nothing to do with performance, but rather curb appeal.
It’s well known that low cost projects like adding nice flower beds to the front of our home can have an outsized return on curb appeal and the selling price of your home. The same principle applies to solar panels, especially if yours face the street.
A great looking solar panel, like the LG NeON 2 Black or any of the several all-black solar panels that are on the market, can make a big difference in curb appeal and the selling price of your home. If selling your home is a possibility during the lifetime of your hoem solar system, appearance is probably the most important factor to consider when selecting between monocrystalline and polycrystalline panels.