Material composition of solar panels

Most bulk silicon PV modules consist of a clear surface, an encapsulant, a backside and a frame around the outer edge. In most modules the top surface is glass, the encapsulant is EVA (ethylene vinyl acetate) and the backside is PET, this is only for glass solar panels, flexible modules may have an ETFE or PET surface and patch modules have a PCB backside.

Surface materials

The front surface of a photovoltaic module must have a high light transmission in the wavelength range that can be used by the solar cells in the PV module. For silicon solar cells, the top surface must have a high light transmission in the wavelength range of 350 nm to 1200 nm. In addition, the reflection from the front surface should be very low. Although in theory this reflection can be reduced by applying an anti-reflective coating to the top surface, in practice these coatings are not strong enough to withstand the conditions of use of most PV systems. Another technique to reduce reflections is to "roughen" or texture the surface. However, in this case, dust and dirt are more likely to adhere to the top surface and are less likely to be dispersed by wind or rain. The components are therefore not 'self-cleaning' and the benefits of reduced reflection are quickly offset by losses due to increased dirt on the top surface.

In addition to the reflective and transmissive properties, the surface material should be impervious to water, should have good impact resistance, should remain stable under prolonged UV exposure and should have a low thermal resistivity. The ingress of water or water vapour into the PV module will corrode the metal contacts and interconnects, thus significantly reducing the lifetime of the PV module. In most modules, the front surface is used to provide mechanical strength and stiffness, so the surface or rear surface must be mechanically stiff to support the solar cells and wiring.

There are several options for surface materials, including acrylic, polymer and glass. Tempered, low iron content glass is the most commonly used as it is low cost, strong, stable, highly transparent, impervious to water and gases and has good self-cleaning properties.

Encapsulants

Encapsulants are used to provide adhesion between the top surface of solar cells, photovoltaic modules and the rear surface. The encapsulant should be stable under high temperatures and high UV exposure. It should also be optically transparent and should have a low thermal resistance.EVA (ethylene vinyl acetate) is the most commonly used encapsulant.EVA is in the form of a thin sheet which is inserted between the solar cell sheet and the top and rear surfaces. This sandwich is then heated to over one hundred degrees to polymerise the EVA and bond the modules together.

Rear surface

The main characteristic of the rear surface of a PV module is that it must have a low thermal resistance and must be protected from the ingress of water or water vapour. In most modules, a thin polymer sheet is used for the rear surface Some PV modules, known as bifacial modules, are designed to receive light from the front or back of the solar cell. In bifacial modules, both the front and the rear must be optically transparent.

The frame

The final structural component of a solar panel is the frame or frame of the solar panel. Conventional frames for photovoltaic modules are usually made of aluminium. The frame structure should be free of bumps that could cause water, dust or other substances to be trapped.