The difference lies in the purity of the Crystallized Silicon (c-Si) used - the more perfectly aligned the silicon molecules, the better the solar cell will be at converting solar energy into electricity. Below is a description of each solar panel type.
Monocrystalline Solar Panels
Monocrystalline silicon cells are made using a layer of single silicon crystals at about 60 cells per panel. The four sides of the single crystalline solar cell are cut out to make silicon wafers that not only optimize performance but also lower costs. They are easily distinguishable for this reason, because the corners of the wafers look clipped, like an octagon (see image).
These solar panels are expensive to make and expensive to buy, but they yield the highest power output compared to other solar technologies. They are also space-efficient as they take up less space on your roof to produce the same amount of power as a polycrystalline or a thin-film solar panel.
Polycrystalline Solar Panels
Here's a fact that will help illustrate the difference between mono and polycrystalline panels, in terms of the solar modules efficiency: REC, a well-known solar panel manufacturing brand, report that while a
Thin-film Solar Panels
Thin-film solar panels, as the name suggests, comprise of a thin layer of photovoltaic material deposited on glass. These panels are the cheapest of the lot as they produce lesser solar power for the same surface area compared to the other two types available. Perhaps for this reason, thin-film solar panels are not commonly used in New Zealand. However, much advancement is being made in the realm of thin-film solar panels.
Ultimately, the type of solar panel you choose for your home largely depends on your cost-benefit analysis. It is nearly impossible to recommend one or the other without studying your situation and the choices you have, thoroughly. You might be working on a shoe-string budget or have roof-space constraints that need consideration. Unless you want to incur the lowest costs possible (and space is not an issue), in which case thin-film solar panels may be the way to go, the decision is usually between monocrystalline and polycrystalline solar panels.