PV Cell Overview
Cells are manufactured from a variety of different types of materials. The most significant is crystalline silicon. There are a broad range of different PV cells produced by over 100 manufacturers. There are four main types of commercially available cells:
- Monocrystalline Silicon PV
- Polycrystalline Silicon PV
- Amorphous Silicon PV
- Hybrid PV
At present monocrystalline PV and polycrystalline PV are the most common and they account for approximately 93% of all modules sold globally in large and small-scale systems. Amorphous silicon accounts for approximately 4.2% of the global market sales.
The fourth type of PV cell, is called a hybrid as it consists of a crystalline cell coated in an amorphous layer.
Monocrystalline Silicon PV
To produce monocrystalline silicon a crystal of silicon is grown from highly pure molten silicon. This single crystal cylindrical ingot is cut into thin slices between 0.2 and 0.3mm thick- this is the basis of a solar PV cell. The edges are cut off to give a hexagonal shape so more can be fitted onto the module.These PV cells have efficiencies of 13-17% and are the most efficient type of the three types of silicon PV cell. However, they require more time and energy to produce than polycrystalline silicon PV cells, and are therefore slightly more expensive.
Polycrystalline Silicon PV
Polycrystalline silicon is also produced from a molten and highly pure molten silicon, but using a casting process. The silicon is heated to a high temperature and cooled under controlled conditions as a mould. It sets as an irregular poly- or multi-crystal form. The square silicon block is then cut into 0.3mm slices.The typical blue appearance is due to the application of an anti-reflective layer. The thickness of this layer determines the colour- blue has the best optical qualities. It reflects the least and absorbs the most light. More chemical processes and fixing of the conducting grid and electrical contacts complete the process. Mass-produced polycrystalline PV cell modules have an efficiency of 11-15%.
Amorphous Silicon PV
Amorphous silicon is non-crystalline silicon. Cells made from this material are found in pocket calculators etc. The layer of semi-conductor material is only 0.5-2.0um thick, where 1um is 0.001mm. This means that considerably less raw material is necessary in their production compared with crystalline silicon PV production. The film of amorphous silicon is deposited as a gas on a surface such as glass. Further chemical processes, the fixing of a conducting grid and electrical contacts follow.These PV cells have an efficiency of between 6-8%. Multi-junction amorphous thin film PV cells with each layer sensitive to different wavelengths of the light spectrum are also available. These have slightly higher efficiencies.This type of PV cell is not currently suitable for use on residential developments due to the low generation density.
Hybrid photovoltaic cells are classified as PV cells that use two different types of PV technology. The Hybrid PV cell shown here is made by Sanyo and comprises a monocrystalline PV cell covered by an ultra-thin Amorphous silicon PV layer.
The advantage of these types of cells are that they perform well at high temperatures and maintain higher efficiencies (18%+) than conventional silicon PV cells. However, these cells come at a cost premium.
Which type of PV do you need?
When choosing a module you need to consider the following:
- That the international product certification is in place (this deals with the quality of the PV modules).
- Manufacturers specifications and warranties for the PV cells.
- Who the manufacturer is, are they reliable? This can usually be determined by customer reviews and testimonials about the service and products. The manufacturer’s length of time in the industry should also give a good indication of their successes.
- What space you have available for the PV development and how much energy you would like to produce? PV will be more beneficial in more energy efficient buildings. Monocrystalline PV and Polycrystalline PV modules can both be successfully installed on residential and commercial properties.
- Monocrystalline PV has a slightly higher efficiency than polycrystalline PV so it may be preferable to use these cells when a smaller surface area is available. Polycrystalline PV should be used when a larger surface area is available as it less expensive. Amorphous silicon PV requires more surface area, however the output is less affected by high temperatures and shading.
Comparison between PV cell types
Hopefully this will leave you slightly more informed about the technology on the market, but if you have any questions, or require more detail please contact our experts, who are happy to go into as much detail as required when explaining your options.