This is a topic I always seem to revisit periodically, and it always starts when looking at the pricing of various “size” panels. There are some pretty long-winded explanations on the Net but this site nailed it on the head without using a ton of Trek techno-babble. So, not wanting to reinvent the wheel but having the desire to share some knowledge, here you go:
Crystalline silicon solar cells come in two main types of Silicon cells. The main talking points with regards to difference are as follows:
Monocrystalline is generally more space efficient than polycrystalline.
A monocrysalline solar panel generally makes a nicer looking solar panel as it is black in color whereas polycrystalline is dark blue in color and “patchy”. The variation of color in the poly structure is similar to plywood where pieces (chips) are formed into a larger whole. These can reflect light differently depending upon the angle the PV cell is viewed at. However, the color of polycrystalline cells has darkened significantly the past few years and it is now looking a lot darker then it used to. As shown below, a monocrystalline cell is displayed on the left, and a polycrystalline cell on the right.
Polycrystalline solar cells generally have a lower temperature coefficient than monocrystalline solar cells. Lets say you have a 1kW of monocrystalline solar array on the same roof and side by side with a 1kW of polycrystalline array. The monocrystalline array will be slightly smaller compared to the polycrystalline array as it is more space efficient. However, the 1kW polycrystalline array will generally generate more electricity over the year when compared to the 1kW monocrystalline solar array because of its better temperature tolerance.
A monocrytalline solar cell usually costs more than a polycrystalline solar cell, however when assembled into a solar panel, the cost of the mono panel is roughly the same as the poly panel in $/Watt.
How They are Made
A monocrystalline rod is created by slowly pulling a monocrytalline silicon seed crystal out of melted polycrystalline silicon. It physically looks like a grey 20cm round rod.
The rod gets cut into wafers and then the round wafers are trimmed to make them more square so they can be arranged nicely on a rectangular piece of glass. To make polycrystalline wafers, molten silicon is poured into a cast where it cools and solidifies. The rectangular block of silicon gets cut into 156mm square wafers so it can be arranged neatly on a rectangular piece of glass. You can tell the difference between a mono and poly panel because of the darker colour of the mono cell, and also the mono cell generally are not perfectly square as they started off in life as a round wafer.
In summary, a monocrystalline solar system will be slightly smaller then a polycrystalline solar system however the polycrystalline solar system will generally generate more electricity.