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301 Moved Permanently

301 Moved Permanently


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Convincing people to go solar used to be fun. You could stick with words like “clean,” “green” and “planet.” It’s all about the planet.

However, a recent article in The New York Times about widespread defects in photovoltaic panels undermining consumer confidence caused a lot of foot shuffling, throat clearing, eye averting and general consternation in the solar sector.

Defects? Suddenly having to argue about PV reliability is not what solar salesmen want to be dealing with right now. It doesn’t matter how pervasive the actual problem is. Perception is king, so it was not surprising to see industry spokespeople swinging into action.

“We in the international solar industry who competitively struggled for decades to maximize solar’s reliability cannot now afford to watch inexperienced producers roll back our amazing progress,” said Raju Yenamandra, SolarWorld vice president for business development, in a statement a few days after the Times hit the doorstep. “Even scattered reports of high defect rates pose a disproportionate risk for the technology and industry.”

Indeed, defects are almost entirely attributable to manufacturing problems. And while it’s easy to point fingers at the new, big kids on the block with their sparkling automated factories and tariff-attracting prices, the fact is that managing production lines to minimize - if not eliminate - PV defects is everybody’s problem.

 

Test, but verify

“Quality is the most important topic facing the solar industry right now,” says Sharon O’Shea, director of marketing at Motech-Americas LLC, echoing Yenamandra’s concern that a lack of confidence in PV products could undermine all of the progress solar has made in the minds of consumers.

“Even though solar power has been around for 25-30 years, we are still at the early stages of quality installations,” she remarks. “A lot of new customers see a certification and think that’s going to protect their investment for 25 years. We know that modules behave differently in the environment.”

Among the production issues facing the industry, even among veteran PV manufacturers with track records like SolarWorld’s and Motech’s, is that the solar power sector as we now know it is a relatively recent phenomenon. According to the Solar Energy Industries Association, installed PV capacity has grown in the U.S. from 4 MW in 2000 to 3.313 GW in 2012, with the overwhelming majority of that growth occurring in the last five years. Consequently, the vast majority of PV customers are new to the game.

Worldwide, solar market growth is just as impressive, with the United Nations Environment Program reporting that global PV capacity exceeded 100 GW in 2012. So, a lot of new PV players rushed into the game, many of them well funded and able to afford top-of-the-line production facilities.

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The consumer electronics industry offers an instructive example of how a new technology, suddenly gaining popularity, found itself held back by manufacturing problems. In the mid-1990s, plasma televisions were appearing as a possible alternative to projection systems to serve the high-end home entertainment market. However, contemporary manufacturing processes were not reliably up to the task of placing thousands of tiny, tightly packed cells in the plasma display matrix. It was a new task, and a significant portion of displays rolling off the line failed inspection.

The high rejection rate for large plasma displays inflated prices. Manufacturing techniques were only able to reliably produce displays comparable in size with high-end cathode ray tube (CRT) displays, and even these were vastly more expensive than the well-established competition. For a time, consumers and professional home electronics installers scoffed at plasma screens.

Only when manufacturing techniques improved sufficiently to reliably increase the cell matrix were plasma TVs able to take off in terms of market penetration. They got bigger than CRTs ever could and, with falling production line reject rates, a whole lot cheaper. Once the manufacturing-line issues were dealt with, plasmas completely eclipsed CRTs in the home entertainment market.

In a sense, the plasma display industry was fortunate that defects in cell arrays were relatively easy to detect. All you had to do was turn the display on, and the defective cells would pop out as persistent anomalous colors or dark spots in a video image. Although correcting the problem required much investment and retooling of production facilities, at least manufacturing equipment makers and process engineers knew where to focus their attention.

When it comes to manufacturing solar panels, problems are much more difficult to detect, obvious cracks and “snail trails” aside. There are many highly regarded PV inspection systems available for the production line, and presumably, advanced factories are equipped with them. These systems are generally optically based, using visible light, thermal or electroluminescent imaging technology. They can see things people would miss. However, they can only see things in the factory.

The challenge as cited by the Times article is not so much that installers are finding PV modules defective out of the box; it is that the performance of the problematic modules is degrading at a much faster rate than predicted. This is not always a defect that is readily observable by human or machine vision.

In turn, it is perfectly plausible for a scrupulously inspected, rigorously tested and independently certified PV module to end up in a desert or a residential roof and still fail long before its time.

This potential blind spot is bringing new testing regimes into the process. The Boston-based Fraunhofer Center for Sustainable Energy Systems and the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg, Germany, say their PV Durability Initiative (PVDI) program is intended to create a database of performance and safety results that could produce more reliable PV modules for deployment wherever they are needed. Under the testing regime, modules are subjected to accelerated stress-testing intended to approach their lifespan for a given set of environmental conditions, such as ultraviolet radiation, dynamic and static mechanical stresses at different temperatures, humidity-freeze cycles and extended periods of damp heat.

 

Don’t drop the BOM

“It’s amazing how many mistakes can be made in the manufacturing of a module,” Motech’s O’Shea says. “The spacing of leads. The crimping tool to add the lead to connect the box to the line. The box may or may not need potting. You have to have somebody who knows what they are doing.”

One of the most important factors of a successfully managed production line is careful attention to the bill of materials (BOM). The BOM is so important and so intrinsic to a PV product’s design that any changes to it are enough to warrant re-­certification by a testing laboratory.

It is not uncommon for manufacturers in the solar sector to change suppliers. At every point in the chain - from wafer to cell, from cell to module and from module to the PV system - materials and component suppliers are liable to supplant each other, often without notice.

“We’ve had situations where a supplier changes the BOM or even the factory,” O’Shea explains. “It does affect our modules. Once, the adhesive just didn’t work. We had been using the same supplier for years. It turned out the supplier had changed factories, and there was a humidity issue in the new factory.”

In that instance, the problem was apparent before the modules left the factory. However, it is easy to envision a situation where a materials problem wouldn’t crop up until the module had been out in the field for a while. O’Shea says inspecting your supplier’s factories is a key aspect of managing your own production line.

And the role of experienced operators and managers on the production line cannot be overstated. Even as factories become more automated, there are many points of human interaction with the modules, such as moving glass for stringing cells or spacing leads on a junction box. Every point of human interaction is an opportunity for a knowledgeable person to make the process better or catch problems before they become catastrophes.

“Institutionalized intelligence is critical in this industry,” O’Shea says.

 

Enlist your customers

One sometimes overlooked source of intelligence in the manufacturing process are customers themselves. After all, they are invested in the success of solar technology and will assuredly complain when things go south.

FLIR Systems Inc., a maker of forward-looking infrared and other thermal imaging systems, says thermal cameras can be used to inspect solar panels in the field for defects under normal operating conditions without having to shut off the power. Although the horse has already left the barn, inspection of an array of panels from a particular supplier could reveal patterns of manufacturing problems that can be traced back to the production facility.

According to FLIR Systems, impurities or gas pockets in the panel show up as hot spots or cold spots in the section observed. Cracks in cells appear as elongations or polygonal patches in the thermal image. The company recommends that the inspector make thermal images of the front and rear faces of the module for comparison and, further, that thermal images should be taken under various load conditions. Any anomalies detected should then be tested electrically.

Not every customer is going to have the inclination or wherewithal to use a thermal imaging camera. However, even residential customers can be part of the quality assurance process. Motech has a buyback program wherein the manufacturer, through the installer, will give customers incentives to enable the company to reacquire PV modules that have been out in the field for a number of years. Such opportunities arise, say, when a roof gets fixed.

“We examine and test the modules,” O’Shea says. “It tells us about engineering issues we need to plan for in updated designs.”

Technology in the PV power industry is always in flux, as is the market itself. In order to manage production in such an environment, manufacturers of PV systems have to take advantage of all available expertise throughout the product lifecycle. Certainly, manufacturers bear a lot of responsibility for how their products are perceived, and thus, for the success of the solar sector as a whole. S

Process: Production-Line Management

Managing Production Defects Requires Detailed Input From All Corners

By Michael Puttré

Experienced personnel on the assembly line with an eye on the manufacturing bill of materials can make all the difference.

 

 

 

 

 

 

 

 

 

 

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