Crystal Quest: Monocrystalline versus Polycrystalline Panels

As promised in the last post, today we’re going to discuss the differences between monocrystalline and polycrystalline solar panels. Before we get into the differences in the crystals, and in the interest of full disclosure, let us tell you about what we use and why.

We here at Sunbird Solar use monocrystalline photovoltaic cells so you probably expect us to tout them as being the best. And you’re right! They are the best for our application. We want to provide the highest output from varying solar conditions with the smallest footprint. This means, in plain English, that in order to remain portable we need to use the technology that works best for all conditions. We cannot optimize for one particular location or even one particular season. Also, panel size and weight have a huge impact on portability, as well. Who wants to lug around a huge, heavy panel with them everywhere they go? We sure don’t.

Yes, monocrystalline is more expensive to produce than polycrystalline, but the end result is a smaller, lighter, better performing panel that maximizes power output.

So why is poly less expensive than mono? Is it junk? Absolutely not. In many use cases choosing polycrystalline photovoltaics is the way to go.

The process of creating polycrystalline panels is less expensive because of how they are cast. Silicon is heated to its melting point, cast, and cooled with a seed crystal. When cooled the silicon branches out forming many (hence, poly) smaller crystals. Therefore the surface isn’t uniform. A uniform surface is more efficient than one that isn’t so it takes a larger polycrystalline panel to equal the output of a monocrystalline panel. Due to the lower cost of the polycrystalline panels, and if you have the space to spare, you may be able to reduce your panel cost while still meeting your power generation goals.

So why is monocrystalline silicon more expensive? The process of creating the cylindrical crystals used in monocrsytalline panels is slower and more involved. Instead of casting the silicon with seed crystals, as in the polycrystalline panels, the seed crystal is slowly pulled from molten silicon. It is slowly cooled as it is pulled until it reaches the proper size and shape. It’s like pulling taffy! This is known as the Czochralski method, which is obviously more involved and exacting than the casting process.

That doesn’t mean polycrystalline panels are bad. Far from it. It just means that you need to choose the right kind of panel for the application you have in mind. For us, with our emphasis on power output and portability, that means monocrystalline panels.

Keith Li
Keith Li