Green Products/Applications

New Technologies Move Solar Industry Toward Grid Parity

September 1, 2009
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Reaching grid parity has long been the goal of manufacturers. While the solar industry has faced a number of challenges to that end, a handful of new adhesive/sealant technologies may help to attain it.

A variety of dispensing equipment allows manufacturers to choose the best material for both production processing and durable finished goods.


What is Grid Parity?

In simple terms, grid parity means that the prime cost of solar energy is equal to the prime cost of generating fossil fuel energy. It’s not the price of operating solar power production, but the total cost - production, labor, initial cost of system components, installation, operation, maintenance, etc.- that is invested to generate a certain amount of energy.

Today, prime costs of fossil fuel are approximately 4¢/kWh, while prime costs for photovoltaic energy are in the 20-80¢/kWh range when spread over a lifetime. The ultimate goal is to have these lines cross. One way to achieve this is to focus on manufacturing more efficient solar modules. However, reducing production and material costs is another major - and necessary - strategy in achieving parity. Thanks to several new adhesive and sealant application technologies, that part of the challenge is becoming attainable.

In-line, automated application of sealants for frames and backrails allows the purchase of cost-efficient, larger-size sealant containers and improves cycle times.

Solar Manufacturing Today

Today’s solar-panel manufacturers are in a precarious position. Although they currently face a slowdown in demand due to the global economic crisis, demand is expected to recover soon, thanks to new incentive programs currently in place worldwide. With lower demand, pricing pressure increases. This means manufacturers need new automated technologies that can help them to stay competitive by reducing costs and increasing production speed. These technologies will also help as manufacturers prepare for the growth in demand predicted for the near future.

Realizing grid parity and empowering solar manufacturers to achieve business success requires technologies that overcome a combination of manufacturing challenges.

Automation
Solar panel manufacturing currently involves intensive manual labor at several stages of the production process. By automating or semi-automating these steps, new technology can reduce production costs and significantly increase product quality. Furthermore, there is a consistency inherent to automated processes that cannot be matched by manual production.

Material Selection
Limited processing technologies have forced manufacturers to use less efficient or effective materials. Currently, manufacturers rely heavily on ambient silicone materials for sealing. These single-component (1K) adhesives cure slowly, which inhibits production speed and increases work-in-process. Manufacturers need technologies that enable the use of smarter materials, including two-component (2K), reactive or hot-melt adhesives, which would allow them to work faster and/or use less material.

Material Sourcing
New technologies enable systems to process larger material bundles, which allows manufacturers to source materials more cost-effectively and increase machine uptime accordingly.

Crystalline vs. Thin Film Modules
While traditional crystalline solar modules can greatly benefit from new production technologies, the newer thin-film modules offer especially promising parity possibilities. This is due to several qualities: they use only a fragment of the photovoltaic material that crystalline modules use; glass, used for the panel’s back and front, is an inexpensive resource; and the thin film module design usually makes manufacturing easier to scale and automate.

Traditional vs. Smarter Materials

Enabling processing of a wider variety of adhesive/sealants allows manufacturers to select the best possible materials for their operations. Certain “smarter” materials achieve their results faster, often using less sealant, which can decrease costs and increase throughput and quality.

The solar industry has been using ambient temperature materials almost exclusively, including ambient-cure adhesive/sealants or tapes. However, hot-applied and reactive materials have enormous potential for solar panel manufacturing.

Materials used for solar manufacturing must:
  • Provide a moisture barrier.
  • Not conduct electricity (in most cases).
  • Be UV-stable (because they sit in the sun).
  • Resist hot and cold temperatures over 25-30 years of service life.
Various hot-melt and reactive adhesives meet these physical characteristics and perform better than the ambient sealants and adhesives being used today. They allow manufacturers to produce product faster because they enable faster cycle times and curing. They are also more cost-effective because they reduce material consumption. By using the right material and application technique, manufacturers can use as little as a quarter of the amount of sealant they currently use.

Reactive adhesives, for example, provide tremendous, lasting bond strength in the face of strenuous use and powerful elements, such as moisture and the intense temperature changes that solar panels must endure. However, the technology to apply these reactive adhesives hasn’t been widely used in the solar industry until now.

Because reactive adhesives begin curing as soon as they are exposed, they must be properly contained and dispensed to prevent premature curing. Without this proper containment and dispensing, adhesive is wasted and products are not bonded or sealed correctly.

In addition, new technologies that enable the use of smarter adhesive and sealant materials also offer the possibility to fully or partially automate, which can increase a plant’s efficiency and capacity.

The basic industry standard is to express capacity of a plant in megawatt output per year. For example, 40 MW means the facility can make 40 MW of panels per year (approximately 350,000 panels, depending on the module technology and nominal power per module). Some plants can only produce 5 MW of panels because all production is manual, but other fully-automated plants have exceeded gigawatt outputs.

Large Material Bundles

Being able to choose the most efficient size of material can be a powerful way for solar manufacturers to reduce costs. Currently, most manufacturers use either tapes or cartridges, which come in various sizes and are mostly used in manual or semi-automated application processes.

These materials come with a variety of challenges. First, they force manufacturers to frequently reload, which interrupts production. Their use can also result in a loss of quality because applying them is typically a manually intensive and, therefore, error-prone process.

In addition, tape is expensive to use. To manufacture tape, a supplier either adds adhesive to the backing that will deliver the adhesive or extrudes material onto a roll. New technologies save money by allowing solar panel manufacturers to use liquefied adhesives, thus eliminating that extra step.

All sorts of adhesives, including 1K RTV silicones, hot-melt and reactive adhesives, are typically offered in larger volumes, which are cheaper due to the ability to buy and use them in bulk.

Liquid butyl application for side/edge seal is a more cost-efficient form and requires less refilling than traditional butyl tapes.

Applications

Side Seal or Edge Seal Application
Thin-film solar panels usually don’t have the added protection of an actual frame, making them more susceptible to moisture. In addition, encapsulation is typically done with EVA, an inadequate moisture barrier. Manufacturers, therefore, need to add an additional moisture barrier called a side or edge seal in the perimeter area of the modules.

Butyl is an excellent moisture barrier typically used for side or edge seal in pre-extruded tape form. When applied as a liquid with new technology rather than traditional tape, butyl offers an ideal, cost-saving solution.

The pre-extruded butyl tape used today is often applied manually or with tape robots. This setup forces manufacturers to refill often because of the limited size of the tape reels. It is also expensive and slow to apply manually. Furthermore, manual tape application diminishes product quality.

New hot-melt butyl processing technologies allow manufacturers to apply butyl adhesive in-line and in liquid form. These technologies also allow for more cost-efficient, larger product sizes that minimize the downtime associated with refilling.

Frame/Backrail Attachment
All solar panels must have components that provide structure and installation capability. Since these panels must tolerate constant sun, wind and precipitation exposure, these components are critical to product performance and endurance. Because of their different structures, this is accomplished in very different ways in crystalline and thin-film modules. Fortunately, new technologies can increase manufacturers’ production efficiencies for both.

On crystalline solar panels, frames provide protection, stable structure and an installation (or carrier) structure. The frame on crystalline modules is typically attached in a completely manual or semi-automated process that uses tape as the adhesive. New technology, however, allows an automated option that applies a framing sealant around the solar module and replaces labor-intensive, costly tape.

Thin-film glass-on-glass modules don’t have frames. In fact, they don’t even have traditional solar cells; photovoltaic material is put on the glass panes as a thin layer or “film,” hence the name. Thin film panels don’t use a back sheet; instead, they typically use a back pane of glass. While this structure makes them stronger, a carrier system still needs to be installed on them, so a backrail must be attached. A backrail is a piece (or pieces) of metal bonded to the back that provides support for installation as well as strength against wind loads.

Although their structures are different, framing and backrailing use similar technologies and materials, and new automated technologies make both processes less expensive and faster, moving these module systems closer to grid parity.

New technologies attach frames or backrails using several in-line glue stations. Like the side-seal application, these technologies allow manufacturers to apply sealant in liquid form and also enable the use of larger-sized sealant containers. This means less-frequent refilling, greater production speed and more cost-efficient material sourcing. These technologies also offer the possibility of automation, delivering faster cycle times, increased productivity and reduced costs, in addition to improved product quality.

Corner Jointing
One of the exciting things about new adhesive and sealant technologies for the solar industry is that they allow manufacturers to improve product quality and performance while keeping costs low. For example, frame corners can be weak spots in the structure that allow moisture ingress. For additional product quality and durability, many manufacturers seal both the frame corners and the edges. New automated dispensing technologies make it possible to add this extra step without adding significant costs.

Junction Box Attachment and Potting
Junction boxes are critical as they are the mechanisms by which energy leaves the module. However, because junction boxes are often connected to the panel with tape or tape-supported cold material, their attachment is an expensive, slow process. In addition, junction box attachment is almost always a manual process, although it’s actually easy to automate.

Another problem to overcome with junction boxes is that electrical contacts don’t mix well with water. One way to protect from possible water seepage is by potting – filling the junction box with a 2K silicone, thus covering the contacts inside the box. 2K silicones provide the quick curing and proper leveling required for potting, but are very expensive.

New technologies allow manufacturers to use alternative materials, such as polyamides or reactive hot melts, that offer an almost instant cure time and reduce the overall cost of the process.

Encapsulation
Advances in encapsulation technology are particularly exciting for solar applications. A typical crystalline module process involves two encapsulants; glass comes in first, then an EVA foil sheet is applied. In most cases, the sheet is pre-cut from a roll or procured as a sheet and placed manually on a glass pane. Next comes a string or array of solar cells on top, and another EVA foil sheet is placed atop the solar cells. Finally, the backsheet material goes on, making a solar sandwich of sorts.

This assembly then goes into a laminator where the whole sandwich, or laminate, is evacuated (air is removed) and the laminate is heated up. This melts the EVA foils until they liquefy. Next, pressure is applied. When this package cools down, an encapsulated solar laminate is formed.

There are several downsides to this process. First, the current lamination technology is always a batch-type process that consumes a lot of energy and typically takes about 10-15 minutes per module batch. Laminators offered in the market can process single modules or up to 10 modules a time, but they still require the same process time. The only way to go faster is to add more laminators that have a large footprint and are costly.

The foils present another challenge. They are usually oversized to ensure coverage of the entire area, so they must be trimmed after lamination. Whether manual or automated, this requires an expensive series of steps that slows down the line.

Nordson is currently investigating and developing application technologies to apply the encapsulant material in-line and in liquid form. Not only will this eliminate the need to hand-cut and trim the foil, it will also speed up the overall process, allowing increased throughput. The ultimate goal is to minimize the process time and energy used for lamination, or, ideally, to eliminate the traditional lamination process altogether.

Parity Can Be a Reality

Solar-panel manufacturing is at a turning point, and grid parity is getting closer. Even the smallest solar-panel manufacturer can begin to benefit from these adhesive and sealant advancements. In addition to incorporation in new solar module production lines, these new technologies integrate easily into any process and can be used to upgrade existing systems.

These technologies help manufacturers reduce production costs and speed production by enabling them to use smarter materials and larger-bundle, industrial sizes in any line. These technologies also offer a cost-effective way to move toward increased automation that provides significant benefits for overall efficiency and quality. Even better, these advancements are all flexible; they can be customized and scaled to meet the specific needs of any line.

For more information, visit www.nordson.com/solarsolutions.

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