Sun-powered electric options were once limited to large dark panels, but now consumers have a choice. In addition to panels of single or multi-crystal solar cells, solar film or thin film solar units are available in frames or in building materials such as roof laminates. Each technology has advantages. The choice depends on budget, space, climate, and aesthetics.
The cells that make up a crystalline photovoltaic module stand out as dark rectangles or octagons. A multi-crystalline cell often appears as a sparkly rectangle. The electrical connections in both technologies show as a pattern of silver lines.
"Thin-film" does not refer to a specific material. These modules can be made of amorphous silicon (a-Si), copper indium gallium diselenide (CIGS), and cadmium telluride (CdTe). Amorphous silicon is popular for applications where looks matter. Since it can be put on plastic, as well as on glass, a-Si can be produce in flexible continuous rolls. Amorphous silicon is used in laminates, solar shingles and roofing tiles.
Aside from appearance and versatility, efficiency is a factor in PV material selection. A convention framed crystalline system will produce more power in less space. The flexible photovoltaic systems, while more aesthetically pleasing, are about half as efficient. This means a flexible module will need twice as much space to generate the same amount of energy as a conventional system.
This has a big effect on system size. A three by three foot solar laminate system can deliver 60 to 70 W, with efficiencies as high as 8%. A three by five foot crystalline module can provide 170 to 220 W, with up to 17% efficiency. But power density is not the only consideration.
Cell temperature has an impact on PV cell power. Crystalline modules lose efficiency at higher temperatures. Solar film units are less sensitive to environmental temperature, losing perhaps 2% of their power at 100F, compared to 6% power loss for a traditional crystalline system. The cell temperature can be modified by allowing for air flow around the system, but if ambient temperatures tend to be high, a thin-film system may be the right choice.
New amorphous silicon modules produce 20% to 25% more energy production than rated. While this will stabilize to the normal rated output within six to twelve months, any system using these modules must be able to handle the initial higher output. Traditional modules stabilize immediately, which eliminates this consideration. Once the a-Si modules become stable, they will degrade at approximately the same rate as other systems.
Not all climates are sunny, so shade and low-light performance may be an additional concern. Flexible sun-powered panel cells can be the same length as the module they are on. These cells are less likely to be completely in shade than crystalline cells, which are usually just five or six inches across.
One type of technology that gives good performance in shade or conditions of low light is that used by Uni-Solar products. These modules are flexible, and have triple junction cells made of amorphous silicon. This technology allows bypass diodes to be used within the module, so that any cell that is in shade can be bypassed. In addition, this arrangement lets each element in the multi-junction cell capture a different wavelength of light. This gives better energy production in conditions where lighting is indirect or not uniform.