The module is encapsulated with tempered glass (or some other transparent material) on the front surface, and with a protective and waterproof material on the back surface. The edges are sealed for weatherproofing, and there is often an aluminum frame holding everything together in a mountable unit. In the back of the module there is a junction box, or wire leads, providing electrical connections.
Conventionally, PV modules are designed and manufactured for outdoor applications. Thus, they can operate under the sun, rain, and other climate impacts, which make possible the use of PV modules as potential components for external enclosures of buildings.
With the development in the past few decades, various types of PV module technologies are now available in the PV market, but not all these technologies are suitable for the integration or incorporation in building envelopes, since PV modules are traditionally designed mainly for power generation, and their functionalities as envelope elements are generally overlooked.
There are currently four commercial production technologies for PV Modules:
- Single Crystalline. This is the oldest and more expensive production technique, but it's also the most efficient sunlight conversion technology available. Module efficiency averages about 10% to 12%[*].
- Polycrystalline or Multicrystalline. This has a slightly lower conversion efficiency compared to single crystalline but manufacturing costs are also lower. Module efficiency averages about 10% to 11%[*].
- String Ribbon. This is a refinement of polycrystalline production, there is less work in production so costs are even lower. Module efficiency averages 7% to 8%[*].
- Amorphous or Thin Film. Silicon material is vaporized and deposited on glass or stainless steel. The cost is lower than any other method. Module efficiency averages 5% to 7%[*]
Module electrical connections are made in series to achieve a desired output voltage or in parallel to provide a desired current capability (amperes) of the solar panel or the PV system. The conducting wires that take the current off the modules are sized according to the current rating and may contain silver, copper or other non-magnetic conductive transition metals. Bypass diodes may be incorporated or used externally, in case of partial module shading, to maximize the output of module sections still illuminated.[citation needed]
Some special solar PV modules include concentrators in which light is focused by lenses or mirrors onto smaller cells. This enables the use of cells with a high cost per unit area (such as gallium arsenide) in a cost-effective way.
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