Understanding the Characteristics of High-Quality Solar Backsheets

The industry is experiencing a drastic but silent changeover from PVDF-based to CPC backsheets, while in the past year, the market share of CPC backsheets was almost 50 percent compared to a mere 12-13 percent initially. This shift is not only due to a high price fluctuation of PVDF but also technological benefits of CPC structures.

Currently, in the PV segment, newer and more efficient solar cell technologies have picked up and hence scientists have also started rigorous efforts to uplift this development from all possible ancillaries that can be made more efficient compared to now. Solar backsheet, being a very critical part of the module, possesses a great potential to contribute to achieving highly efficient and reliable modules. 

Being on the field for over a decade, proving its competence with reliable performance, CPC structures have started gaining momentum to stay long in the PV industry. Most of the top module manufacturers have already started or done the certifications with CPC backsheets for all their new-generation models. In this scenario, it will be motivating for Indian solar module manufacturers to benchmark their models with giants and survive in the competitive price/Wp market. 

While the industry is looking ahead with the alternatives to PVDF, some of the basic characteristics of the backsheets will be required to match from day 1. 

A backsheet is a backplane component of the solar panel that serves as mechanical, thermal and electrical support. In other words, it acts as a first line of defence for solar modules and hence must possess some of the important characteristics like:

Electrical Insulation: A backsheet can come in direct contact with humans in the field and hence it must possess extremely high electrical insulation. The backsheets must be designed to withstand high leakage currents without significantly discharging them to their outer surfaces. Most obviously this function is performed by the heart of any backsheet, e.g. PET layer. Unlike laminated backsheets, coated ones also use these traditionally proven base layers which offer excellent dielectric strength and minimize the perturbations from external stimuli, especially from humidity and heat.

Weatherability: Apart from glass and frames, the backsheet is the only component that comes in direct contact with environmental stresses like wind, hail, UV, humidity, and heat. To date, the air side layer of the backsheet made up of fluoropolymer is superior in terms of resistance to extreme weather conditions. This is because of the very high chemical resistance of such material due to which longevity of fluoropolymers is superior compared to other available options. In CPC backsheets this protection comes from both sides i.e. air and cell sides which makes them a superior choice when it comes to the stable and safe operation of a solar module.

Hydrophobicity: Backsheets are designed to sustain in any harsh environments including extreme heat, humidity, cold, snow, mechanical or chemical loads and UV exposure. Though it is very difficult for a single-type backsheet to sustain in all these conditions, fluoro materials have a special advantage due to their inherent chemical structure. One of the most important parameters for any backsheet is its water vapor transmission rate, commonly known in the PV industry as WVTR. Any type of backsheet one may opt for which offers WVTR as almost negligible, i.e. as per standard practice < 1 gm/m2 day. Alishan-coated backsheets come with superhydrophobicity which is nearly 5-7 times better than any of the laminated options that exist in the market. 

Mechanical Stability: A very high ultimate tensile strength of PET-based backsheets is one of the obvious reasons for the industry to rely upon it. These backsheets can withstand the stress and strain conditions during manufacturing, handling, transportation, and lamination. Moreover, these backsheets offer excellent adhesion with encapsulants, which is vital for the overall stability of the solar module. Coated backsheets are inherently excluded from a variety of degradation modes like chalking and blistering all thanks to their superior innate mechanical strength. 

- Nikhil Agrawal, Director, Alishan Green Energy Pvt. Ltd.