The PV and solar industries have technically met the challenge of grid parity in many geographical locations and yet there is still hesitancy in the uptake of this renewable resource. Despite the advances in the technology the manufacturing process can often be expensive enough to make the margin of return and profit too much of a risk for some looking into the industry. American-based LORD Corporation discusses how their knowledge and history with structural adhesives could provide a more cost and technology effective solution for panel manufacturing.

Harnessing the sun's energy to produce electricity is once again garnering interest from eager consumers looking for a cheaper, environmentally-friendly power source. During the last energy crisis of the 1970s, solar power gained attention as an alternative to more costly fossil fuels, but the high cost of producing solar energy at that time made it impractical for most consumers, especially for large installations.

However, according to the Solar Energy Industries Association (SEIA), due to current concerns about rising costs, energy security and supplies, coupled with new state and federal incentives, the solar energy industry has seen tremendous growth since 2005. The U.S. now ranks fourth in the world for cumulative installed solar capacity, after Germany, Spain and Japan. Solar energy is the cleanest, most abundant, renewable energy source available and making solar systems more cost-effective will expand consumer availability.

One of the methods for harnessing the sun's rays is through photovoltaics (PV) – converting light into electricity. Photovoltaic devices consist of an array of cells containing various materials (such as an active silicon layer) that turn solar radiation into direct current electricity. To produce enough power for very large applications, such as a home or a commercial business, cells are electrically connected to form photovoltaic modules or solar panels.

Structural Adhesive Advantages

Although PV manufacturing is expanding in the U.S., along with the number of installed solar systems, manufacturers and distributors are continuing to seek out new methods of cutting manufacturing and installation costs. A growing solution that has proven to streamline costs, decrease maintenance, and improve durability and product life expectancy of PV systems is the transition from mechanical fasteners to structural adhesives for PV panel manufacturing and installation.

As an alternative to mechanical fasteners, structural adhesives offer the benefits of reduced stress points, leaks and corrosion; resistance to extreme environmental conditions; and enhanced sealant properties. Structural adhesive bonding is an established joining method, proven in a variety of end-use markets, including cars, trucks, specialty vehicles and boats. By switching to structural adhesives, the PV panel industry can realize significant cost savings in both manufacturing and installation.

Manufacturing with Adhesives

"The solar industry has been growing rapidly over the past few years and is well positioned to make a significant contribution to the future energy supply in the United States," stated Ian Quarmby, an Innovation Scientist at LORD Corporation, a producer of general-purpose and specialty adhesives and coatings. "There are many areas of solar panel construction where structural adhesives would be a viable alternative to mechanical fasteners including the assembly of PV panels and in the supporting framework structure." In photovoltaic cell production, the active silicon layer is often sandwiched between two glass panels. A metallic or composite frame encloses the panels; the frame connects to a rack or framework structure that supports the panels. The racks may be affixed to single- or dual-active tracking systems that allow the panels to follow the sun.

"For the manufacturing of PV panel systems, structural adhesives can be applied between the glass and the metallic or composite frame, and also used to attach the frame to the rack," noted Nicole Wood, a Business Development Manager at LORD Corporation. "The structural adhesives are a cost-efficient, durable alternative to mechanical fasteners such as U-bolts and screws."

LORD Corporation's adhesives have an measured history of durability throughout the lifetime of an assembly. Its automotive adhesives have been in use for over 25 years without any corrosion issues; and its metal-bonding adhesives are in use in applications such as aluminum-skinned satellite dishes, commercial signage and land-based military transport vehicles, where thermally-induced stresses and wind loads create fatigue conditions.

The company also has had an established presence in the solar energy industry for almost 30 years. For example, its Versilok^® adhesives have been used in the manufacture of heliostat mirror modules, which convert solar energy into thermal energy and then into electricity. Versilok adhesives impart a strong bond, act as a sealant and cure quickly, and are able to withstand severe environmental conditions.

Furthermore, structural adhesives offer a processfriendly solution that can save time and money, while increasing product quality. "Depending on the assembly process or the speed of the assembly process, a manufacturer can apply the adhesives from a manual cartridge or a very sophisticated, high-speed robotic system," Quarmby said. "We can show PV manufacturers how structural adhesives can optimize their production process and deliver a better product, and assist them with implementing process changes for converting to adhesives."

Installing with Adhesives

But it's not only photovoltaic panel manufacturers that can reap benefits from switching to structural adhesives; the installers of these systems will also find advantages in using adhesives in place of mechanical fasteners. For example, consider the number of mechanical fasteners used on the average photovoltaic array. In many cases, there are hundreds of bolts connecting the array to the racking and tracking systems. These bolts require continual maintenance in order to ensure the operating integrity of the solar panel system.

"Installers offer panel warranties to their customers, usually from five to 20 years, for the installation, but they require the consumer to purchase an agreement plan," explained Wood.

The mechanical fasteners, used to secure the photovoltaic arrays to the supporting racks and tracking systems, loosen over time due to windinduced and/or structural vibration. Structural adhesives not only eliminate the problem of loosening fasteners, but also eliminate the need to visit an installation site for maintenance follow-ups. Another concern for solar panel installers is the weight of the system. Structural adhesives eliminate the weight of mechanical fasteners and improve stress distribution, while providing a clean, streamlined appearance.

"Another potential benefit to PV installers and manufacturers is a reduction in inventory," Wood commented. "They can replace their huge inventory of bolts, washers and screws with one structural adhesive kit."

An Easy Choice

Although structural adhesives are a proven, established substitute for mechanical fastening, some manufacturers and installers might still have a few doubts about their viability in solar panel systems. Solar panel systems must be able to withstand extreme heat, high winds and severe weather conditions for the life of the installation. "Because LORD Corporation's structural adhesives maintain high bond strength performance in harsh environments, they are ideal for use in assemblies that will be exposed to extreme environmental conditions," Quarmby said. "In addition to realworld longevity, our structural adhesives are put through rigorous specification testing including exposure to corrosive environments, water soaks and cyclic fatigue testing."

"Some installers might be concerned about the labor requirements for using structural adhesives," said Wood. "There is a perception that adhesives require more skill to apply than a simple mechanical fastener."

Wood explained that skilled labor is not necessary, and in less than one half-hour, a person can be taught how to mix the adhesives and use the bonding equipment. By switching to structural adhesives, installers will reap the benefits of less installation time and decreased maintenance, while improving product durability.

Quarmby and Wood concurred that the cost savings can be significant when using structural adhesives for solar panel assembly and installation. "When you consider the number of mechanical fasteners required to secure an array to a rack or tracking system and then compare that to a single structural adhesive which requires few installation hours and no follow-up maintenance, the choice becomes easy," Quarmby stated.

Saving Solar Energy

According to the SEIA, "the greatest challenge the U.S. solar market faces is scaling up production and distribution of solar energy technology to drive the price down to be on par with traditional fossil fuel sources." As a less expensive, environmentally-friendly energy source, solar power is slated to become even more prominent in the United States as other energy supplies become more costly and less obtainable.

For photovoltaic panel manufacturers, using structural adhesives in place of mechanical fasteners will help them to build a better product, faster, more simply and with less cost. Solar panel installers will find using structural adhesives can eliminate the problem of loosening fasteners while providing the benefits of little or no maintenance and less labor requirements.

"There is a push for corporations to 'Go Green,' " Wood said. "Companies are adopting sustainability themes and their shareholders, employees and communities are all interested in environmentallyfriendly practices. The U.S. government is also investing large amounts of money in renewable energy research to replace fossil fuels, and solar energy fits right into the equation."

"For the solar energy industry to be really successful, it is imperative that it continues to lower costs, whether at the module level or the installation level," concluded Quarmby. "Structural adhesives offer the potential for cost-savings, along with the reassurance of product durability and environmental stability."