Know what to look for when shopping for quality solar panels
By Michael Sullivan, marketing communications team at DUNMORE Corporation.
What is so important about the back of a solar module? At first glance, the backsheet appears to be a simple layer of plastic film on the back surface of the module. However, when you consider that this is the only layer of protection from dangerous DC voltage, it’s clear why a quality backsheet is important.
Significant development, testing and standardization is involved in the design and testing of the materials used in backsheets. A poor quality backsheet can result in catastrophic failures and pose serious threats to installers and maintenance workers. Also, once the array is installed, a poor quality backsheet can lead to system degradation, unwanted or unplanned maintenance, and replacements and additional unplanned and unbudgeted costs.
Over the past few years there have been some high-profile changes in module manufacturing, with many players going out of business. For those manufacturers who remain, this drastic industry churn underscores the need for the safest, longest lasting and reliable materials available for module construction, including backsheets.
Take a closer look at the stressors the backsheet will face over its expected 25-year lifetime. Just the amount of time a solar module is operational poses its own set of challenges. Modules are expected to last, with little to no performance degradation, from 10 to 25 years. Development and testing ensures that this seemingly thin piece of plastic film will last that long and keep the electrical components inside shielded from the environment.
What Does The Backsheet Do?
The backsheet is typically a laminate of different polymer materials. The panel’s backsheet serves the same function that wire insulation serves in household wiring: to insulate and protect the user from shock and provide the most reliable and efficient electrical conductivity possible. While it acts as an electrical insulator, it must also protect against the following:
• Ultra-violet radiation, which is harsh on most polymer materials
• Temperature swings from -40°F to +185°F
• Humidity and vapor incursion
• Dryness, wind, dust, sand and chemicals
• Scratches during installation and maintenance
To accomplish this, the backsheet uses different materials laminated together, each with a specific role, to create a single laminate.
As the diagram illustrates, the outermost layer provides the outside protective layer (or “shell,” as it’s commonly known). It’s the first defense against environmental exposure, such as moisture, UV radiation and thermal cycling. The second (or core) layer provides secondary support to the outside layer and additional electrical insulation from the cell side. The cell-side layer provides additional protection from electrical voltage. It also serves as an adhesive, and hermetically seals the silicon wafers (which transmit solar energy as DC current) and protects them from short circuits and other malfunctions.
Silicon wafers used in PV modules are extremely thin and sensitive. They are layered with “strings and tabs” that conduct the electrical current out of the module and into a transformer. These electrical pathways are extremely vulnerable to breakage until they are vacuum-laminated to the cell-side layer of a backsheet. This lamination is what holds the entire module together to function as an electrical generator, which is why the backsheet is so critical. If any of these materials is not absolutely fit for the function it serves, the entire module will fail prematurely.
What Do You Look For In A Panel?
First, always look for certified materials. Certification organizations such as Underwriters laboratories, TÜV Rheinland and Intertek require modules to go through a battery of tests to ensure minimum safety requirement are met. These include accelerated damp-heat and thermal-cycling tests. Also, QUV tests are performed to simulate wear and tear of sunlight, air, water and other environmental exposures that may eventually break down the module with repeated exposure.
All the materials are tested in a constructed module to obtain this certification. Any time a module is redesigned it must be recertified. Even if the manufacturer changes materials that they claim as identical to the original module, the company must have the certification agency review the changes and re-certify as appropriate.
Most manufacturers may be reluctant to give you the entire construction of the materials, but they must provide you with test reports for the recertification of the module that exactly match the products you will be installing. Do not ever install modules without confirming they are certified by a recognized standards body or you or your team could risk installing PV modules that are not up to essential safety and performance standards.
What Questions Should Contractors Ask Module Manufacturers?
1. Always ask for the certification, typically either UL or TUV. Never compromise on this part of your decision making progress.
2. When were the modules manufactured? (Older inventory may have been stored in unfavorable conditions. Be aware of when the product was made).
3. Do the modules have serial numbers? They normally do. Make sure they are on the module or any product documentation.
4. What warranty is stated in writing and provided with the product?
5. What does the warranty not cover? This is important for any weakness the module maker would not want you to know about.
6. What is the defective product replacement policy? Make certain that defective products are replaced, including shipping costs to and from the installation site.
7. What test data is available for the modules? All modules must tested at the factory for function. This is recorded and attached to the module documentation.
8. As always, the lowest price is not always the best option. Consider carefully your materials, the financial reliability of your supplier and the detail of the product documentation.