Most crystalline silicon technologies (Mono or Poly crystalline) yield similar results, with high durability and long life. Twenty-five-year warranties are common for crystalline silicon solar panels. Monocrystalline tends to be slightly smaller in size per watt of power output, and slightly more expensive than polycrystalline.
The construction of solar panels from crystalline silicon cells is generally the same, regardless of the technology. The most common construction is by laminating the cells between a tempered glass front and a plastic backing, using a clear adhesive. It is then framed with aluminium.
The silicon used to produce crystalline modules is derived from sand. It is the second most common element on earth, so why is it so expensive? The answer is that, in order to produce the photovoltaic effect, it must be purified to an extremely high degree. Such pure “semiconductor grade” silicon is very expensive to produce. It is also in high demand in the electronics industry because it is the base material for computer chips and other devices. Crystalline solar cells are about the thickness of a human fingernail. They use a relatively large amount of silicon.
Monocrystalline Solar Panels
Monocrystalline (Single Crystal) is the original PV technology invented in 1955. Monocrystalline solar panels are composed of cells cut from a continuous crystal. The silicon crystal forms as a cylinder, which is sliced into thin circular wafers. The cells may be circular or may be trimmed into square(ish) shapes, to minimise unused space on the solar panel. Because each cell is cut from a single crystal, it has a uniform dark blue colour. Monocrystalline solar cells can achieve an efficiency of up to 17%, but commercially available panels are usually around 14% – 16% efficient.
Polycrystalline Solar Panels
Polycrystalline (many crystals) cells were new to the market in 1981. They are similar in performance and reliability to Monocrystalline. Polycrystalline cells are made from a similar silicon material, but are melted and poured into a mould to form a square block that can be cut into square wafers with less waste of space or material than round single-crystal wafers. As the silicon cools, it crystallises, but forms random crystal boundaries. Their efficiency of energy conversion is slightly lower than Monocrystalline cells. This means that the size of a Polycrystalline solar panel is slightly greater per watt than most Monocrystalline solar panels. Polycrystalline cells look different to Monocrystalline solar cells.
The surface has a random appearance with significant variations of the blue colour. Efficiencies of up to 16% are possible.
Thin Film Solar Panels Aka Amorphous Solar Panels
Thin Film Solar Cells (also known as “amorphous”, meaning “not crystalline”) were first produced in 1976 These PV cells are made with microscopically thin deposit of silicon, instead of a thick wafer. This uses very little silicon. It is generally deposited on a sheet of metal, plastic or glass. The individual cells are deposited next to each other, instead of being assembled. The active material may be silicon, or it may be a more exotic material. Thin film panels can be made flexible and lightweight by using plastic glazing. Some flexible panels can tolerate a bullet hole without failing. Some of them perform slightly better than crystalline modules under low light conditions. They are also less susceptible to power loss from partial shading of a module.
The disadvantages of thin film technology are lower efficiency (commercially available panels have efficiencies of ~9%) and uncertain durability. Lower efficiency means that more space and mounting hardware is required to produce the same power output. At this stage, thin film materials tend to be less stable than crystalline, causing degradation over time. We will be seeing many new thin film products introduced in the coming years, with efficiency and warranties that may approach those of crystalline silicon.
It is believed that crystalline silicon will remain the “premium” technology for critical applications in remote areas. Thin film will have strong growth in the “consumer” market where price is a critical factor, but this must be balanced against the additional collection area needed for the lower efficiency thin film panels and the likelihood of shorter operating life.
As usual, you get what you pay for.
If you wish to learn more about how a solar panel works, howstuffworks.com has a good tutorial on this topic.