Types of Solar Panel
The silicon cells are fragile and brittle, so they are built into a sandwich construction behind a glass cover sheet to provide protection from mechanical damage. The cells are encapsulated between films of polymer protecting the cells from the effect of moisture which would corrode the electrical connections.
Cells are connected in series by flat strips of copper soldered onto the front face of one cell and the rear face of the next. To complete the PV panel or module, a frame of extruded aluminium is fitted around the edges of the glass sheet to protect and stiffen the panel and provide a means to fix down.
There are a number of different types of silicon-based cell that are used in the construction of PV panels, but the main three that are in common use are: –
Monocrystalline(mSi)
These have cells which are cut from a single crystal of silicon, so they are effectively a slice from a crystal.
In appearance, it has a smooth texture and the thickness of the slice can be seen. These are the most efficient of the three and they are the most expensive to produce. They are also rigid and must be mounted in a rigid frame to protect them.
With Mono panels, wafers are cut from a single ‘ingot’ of silicon crystal, making the surface of the crystal flatter. Light hitting the panel is therefore perpendicular to the surface. This increases the efficiency of the panel, the effect of which is to produce more power in a smaller area.
Polycrystalline(pSi)(Multicrystalline)
Polycrystalline panels have cells that are a slice cut from a block of silicon consisting of a large number of crystals.
They have a speckled reflective appearance and again you can see the thickness of the slice. These cells are slightly less efficient and less expensive than monocrystalline cells; again, they tend to be mounted in a rigid frame.
This technique uses fragments of silicon crystal melted together. Poly is an older technology, cheaper to produce and has a blue shade to it. Because there are edges where the crystal fragments meet, there are small areas that are not perpendicular to the light hitting the panel, meaning they don’t absorb energy, resulting in slightly reduced efficiency.
Amorphous
These cells are manufactured by placing a thin film of amorphous (non crystalline) silicon onto a wide choice of surfaces.
These are the least efficient and least expensive to produce of the three types. Owing to the amorphous nature of the thin layer, it is flexible and if manufactured on a flexible surface, the whole solar panel can be flexible.
One other characteristic of amorphous solar cells is that their power output reduces over time, particularly during the first few months, after which time they are basically stable.
