In short: Most solar panels are made from silicon solar cells encased in glass and surrounded by an aluminum frame. But the details matter! Modules can be made with either polycrystalline or monocrystalline silicon, and many so-called “thin film” panels are made without silicon at all! Read on to learn the differences between the types of solar panels and the best ways to use each kind.
A solar panel (more commonly known in the industry as a “solar module”) is a piece of equipment that generates electricity from sunlight by converting photons of solar energy into “excited” electrons that flow through wires. This conversion of solar energy into electricity is called the “photovoltaic effect,” and it requires a few things to work properly: two kinds of semiconducting material and a way to connect them over a wire.
OK, that might sound a little complicated, so here’s what you need to know about how solar panels work:
- A semiconductor is a substance that conducts electricity better than rubber and glass, but worse than metal.
- Silicon is the semiconductor everyone uses because you can find it everywhere on earth (Really! It makes up over 25% of the earth’s crust).
- By adding stuff to the silicon, you can give it a negative charge (has extra electrons) or a positive charge (attracts electrons).
- Sunlight can be used to knock the extra electrons off of the negatively-charged silicon, which then will gladly flow along a metal wire to get to the silicon that attracts electrons. The flow of electrons is electricity!
- If you connect a thing that uses electricity (light bulb, toaster oven, refrigerator) to the wire, electrons flow through it and the thing starts working!
So that’s the jist of how solar modules work. It’s more complicated than that, of course, but now that you know that, you’re ready to learn about solar modules made with different materials.
Monocrystalline vs Polycrystalline silicon
First stop on our tour: silicon solar panels! Like we said above, silicon is abundant on earth, but not in a perfectly usable form. In order to make silicon into solar cells, it has to undergo one of two processes to become crystalline silicon.
Polycrystalline silicon is the “easiest” to make. First, a bunch of chunks of silicon are put in a big heat-proof container. Second, the silicon chunks are baked in an oven until they melt together, then removed to cool off.
The reason it’s called “polycrystalline” is because those chunks don’t all melt 100% of the way, and as the silicon cools, it forms multiple separate crystals (“poly” means “multiple”). The big block of melted silicon is cut into slices called silicon wafers that look like this:
The polycrystalline wafers are “doped,” or covered in different chemicals that gives them the negative or positive charge we discussed above. Then a network of tiny wires are added to carry the electrons released by the photovoltaic effect.
The cells are wired together into groups (usually of 60 or 72 cells) and encased in UV-resistant EVA plastic, then sandwiched between layers of glass to make solar modules.
Ok, rewind! Monocrystalline silicon is harder to make, but the process results in cells that are better at converting sunlight into electricity (they have higher “conversion efficiency”).
In this case, the silicon is melted at a much hotter temperature in a huge vat, and a “seed crystal” is lowered into the vat. The silicon cools around the seed crystal as it’s slowly rotated and pulled out, forming into a single crystalline structure called an ingot.
The monocrystalline ingot is a cylindrical rod of silicon about 8 inches wide and up to 6 or 7 feet long. To make monocrystalline silicon cells, the ingot is first shaved down to give it an octagonal shape with four wide flat sides and 4 short flat corners, then sliced into cells only 100 micrometers thick.
The cutting of the ingot gives the cells their distinctive octagon shape. In fact, the easiest way to tell if a solar panel is made with mono- or polycrystalline cells is by looking at the shape of the cells. If there are little diamond-shaped white spaces at the corners, you’re looking at a mono panel.
Advantages and disadvantages of different types of solar panels
In general, choose mono panels if you want more aesthetically pleasing panels that can produce more electricity in less space. Choose poly panels if you want the lowest cost and have plenty of space for them.
Pros and cons of monocrystalline solar panels:
- Because one crystal structure is used to create the wafers, mono solar panels have the ‘purest’ type of silicon and thus have the highest efficiency (up to 22%).
- Because of that high efficiency, a mono solar panel system uses less space on the roof or ground.
- They have the longest life span; well over 25 years.
- Monocrystalline solar cells are the most expensive solar panels, and cost between 5 and 10 cents more for every watt generated than polysilicon panels.
- Due to the cutting process, mono panels generate the highest amount of silicon waste.
- The panels are more sensitive to shade and dirt/snow cover.
Pros and cons of polycrystalline solar panels
- A simpler manufacturing process makes poly solar panels the cheaper option for homeowners.
- Polycrystalline solar panels are slightly less sensitive to direct heat than monocrystalline panels.
- Since the ingots aren’t cut to shape, poly panels produce much less silicon waste.
- Polycrystalline solar panels are less efficient than monocrystalline panels; they typically top out at 16% efficiency.
- Due to their decreased efficiency, poly panels need more space to generate the same amount of power as mono panels.
- For people who care about how solar panels look, poly panels’ mottled blue hue doesn’t have the same “curb appeal” as the solid, sharp look of mono panels.
What about thin film solar panels?
Oh, you’ve heard about thin film, eh? The promise of a flexible plastic solar sheet that can be wrapped around everything from buildings to boat hulls is intriguing, but the film doesn’t need to be flexible, or even plastic. The “film” in thin film actually refers to how the semiconductor is applied to whatever surface is used to hold it.
Because of that detail, thin film solar can be any of a number of different semiconductor materials attached to a plastic or glass substrate.
Theoretically, these technologies can produce long-lasting, lightweight solar panels with less material, but in practice, each variety of thin film solar has its own issues. Here’s a quick rundown of what’s out there:
Current Thin Film Solar Technologies
|Semiconductor||Information, pros and cons|
|Amorphous Silicon (a-Si)||The most similar to traditional silicon solar panels, a-Si involves applying a chemical mist of silicon to glass or plastic. The best a-Si panels are only about 60% as efficient as traditional silicon panels.|
|Cadmium Telluride (CdTe)||The most widespread thin film solar technology. CdTe panels can be almost as efficient as traditional silicon (but usually aren’t). Cadmium is a relatively toxic chemical and disposal is a major concern. Note: First Solar, the maker of most CdTe panels, offers free recycling at end-of-life.|
|Copper Indium Gallium Selenide (CIGS)||CIGS is a newer technology that can be nearly as efficient as traditional silicon solar, but is not currently widespread.|
|Gallium Arsenide (GaAs)||Are you sending a probe to another planet or trying to win a solar car X prize? Choose Gallium Arsenide. GaAs is a highly efficient semiconductor but the process to make solar panels from it is quite costly.|
Advantages of thin film solar panels
In general thin film solar has three advantages:
- Manufacturing thin film solar products uses much less material than traditional silicon solar manufacturing.
- Thin film can come in many shapes and sizes, and can be bent or wrapped around whatever it’s installed on.
- Thin film solar panels generally maintain their efficiency at high temperatures (though they often start out at lower efficiency in the first place).
Disadvantages of thin film solar panels
As we mentioned in some of the write-ups above, most thin film solar panels are less efficient than mono- and polycrystalline solar panels, meaning they take up more space to generate the same amount of electricity.
Which of the types of solar panels is best for your home?
If you’re looking to install solar, choosing a reputable brand with a comprehensive long-term warranty will likely be much better for you—and your wallet—than choosing a specific type of solar panel.
And you might not have much of a choice to make. Most installers are now quoting home solar systems using only mono solar panels in all the solar systems they install. When you get quotes for solar, your installer will likely present you with a choice between two price points that only differ in the brands of panels and inverters included.
It’s no secret that monocrystalline solar panels are the “best” choice on an equal playing field — but they can be unaffordable to some people, and they produce a lot of waste. It’s encouraging to know that more affordable, cleaner solar panel types exist for any homeowner who simply wants to do good for the planet, and save money while they’re at it!
What else should you know about home solar panels?
Whether you choose mono, poly or thin film, there is very little difference between the types of panels when it comes to maintenance. All types of solar panels require very little maintenance in their lifetime!
You need to know how to choose a solar installer. We put together a handy checklist for finding a great solar installer and warranty.
If you’re feeling indecisive, let us and our trusted installers help choose for you!
Last modified: October 2, 2019