By Antje Stephan

Customers often base their decision on nominal efficiency factors or the price per watt peak. These are, of course, two important criteria, but, from a long-term perspective, simply not enough. After all solar installations must last for 25 years. And they will too, provided they are installed correctly, and are of good quality. But how do you actually recognize good quality in a solar panel?

For Karl Heinz Kusters, R&D Manager at Conergy in Frankfurt (Oder), quality panels must fulfil three criteria: They must be high-yield, solid and safe.

The solar cells themselves are responsible for the yield factor. Innovative cell designs can deliver efficiencies of 16 to 23%, depending on material and processing effort. The market is currently dominated by cells with two metallic collector contacts on the upper side, the so-called ‘busbars’. Some manufacturers print three busbars instead of two onto their solar panels to allow for more efficient dissipation of the generated power. Karl Heinz Kusters sees definite benefits in improved power distribution, “Three busbars help to reduce contact resistance between the cells. The result is an increased, and more consistent module efficiency.” Kusters, who holds a doctorate in physics, also believes that combined with suitable cell connectors, the use of three busbars provides more reliability in terms of power generation.

He and his expert colleagues favor bypass diodes when it comes to module manufacturing.

“They function like a protection switch for the cells. If, for example, foliage should shade individual cells, the bypass diodes will channel away power, thus protecting the shaded cells.

Once sunlight is no longer impeded, the bypass diodes switch back to their original mode, and the module will once again work at full capacity,” explains Kusters.

High-Quality Components Provide Stability

But even the highest yield is of little use if the module doesn’t last for its projected 25-year lifespan. The production process must lead the way into the right direction. Premium quality components, like specialist solar glass and a robust frame, provide the necessary protection for the fragile cells.

But, even for solar glass, the choice is endless: Smooth, unstructured, micro-structured, heavily structured or even specially coated glass is on offer. Each and every glass type is designed to conduct as much sunlight as possible into the solar module. Conergy’s technical director explains, “Heavily structured glass types tend to attract contaminants, which over time will lead to a decrease in the module’s capacity. For European latitudes, microstructured solar glass is better suited, because it self-cleans in the rain.”

The module frame stabilizes the solar module, and protects both the glass and the cells. The most robust frames are those made from anodised aluminium. They are much more scratch-resistant than coated frames. Kusters also warns about possible hazards due to hollow enclosures, “Frames should not have any hollow enclosures, as these could collect water, which can then turn to ice in the winter. As a result, the frame could buckle or even burst.”

A flat run-off edge facing away from the cells can also help avoid snow and ice deposits, which could lead to the frame disconnecting from the module. In summer, contaminants like pollen or dust will find no adhesion, which means that moss growth can be avoided.

Contaminant of that type can be particularly critical, as they will permanently shade cells, which will result in a significant loss in module capacity─and in consequence in output of the entire solar installation.

The combination of solar glass and frame should also be fairly robust. Particularly in regions prone to heavy snowfall, solar modules are often exposed to high surface loads. According to Kusters, a good solar module should be able to withstand surface loads of at least 550 kilogram per square meter─that would be more than three meters of snow in the winter.

The safety aspect is one of the most important criteria to bear in mind when shopping around for solar modules. Karl Heinz

Better Safe than Sorry

Kusters, Technology Director at Conergy, therefore, advises customers to pay particularly close attention to the junction box. Faulty construction or poor workmanship can, under certain circumstances, create a fire hazard for the entire solar plant. “I generally advise against clamp, plug or screw connections. These could easily come undone or corrode if installed improperly. The resulting arc could cause the junction box to catch fire.” Instead, he recommends moulded junction boxes made from non-flammable plastic with soldered connections. These are moisture-protected and vacuum-sealed, providing a maximum of safety.

Solar module manufacturers offer many safety options: Warranties, certifications, and positive capacity tolerances. The actual scope of services provided, is determined individually by each manufacturer. A warranty period of five years for solar modules should, however, be the absolute minimum offered.

Kusters also recommends, “If the solar modules will be deployed in regions with severe weather conditions, customers should look for additional certifications, like ammonia resistance, or for special certifications regarding corrosion-resistance if the solar modules will be installed in coastal regions.”

The International Electrotechnical Commission (IEC) has developed safety standards for the international trade in solar panels. In Germany, the IEC standards 61215 and 61730 apply for crystalline modules. They guarantee that the module’s design is approved and safe. Also the manufacturers should be relevantly certified. A certification of the production facility in accordance with ISO 9001 and ISO 14001 will guarantee the manufacturer’s compliance with environmental regulations, and the use of a quality assurance system to safeguard the quality of the manufactured modules. Kusters is convinced that only those manufacturers, who maintain a premium quality production facility and production processes, will actually produce high-yield, robust and safe solar modules. Only those will be the kind of modules that will last for the promised number of years.

The PowerPlus Modules

Conergy has incorporated its 12 years of solar experience in its premium modules. The PowerPlus modules are actually the result of the solar company’s history. Conergy started as a trading house and systems integrator─selling nearly all components available at the market. When becoming a systems manufacturer in 2007, the solar experts incorporated all this knowledge in their PowerPlus modules manufactured in Frankfurt (Oder), Germany.

They eliminated the known weaknesses and included the strengths of the modules they have traded in the past. And the PowerPlus modules prove the Conergy experts to be on the right path─with all its quality seals, test results and extremely low return rates. Here, the numbers speak for itself: The return rate on Conergy PowerPlus modules is 0.0037%.

Moreover, the product has a standard 5,400 Pascal load capacity. This is the equivalent of 11 people standing on the module at the same time without causing any damage. The robust workmanship of the solar module which is entirely manufactured in Germany was additionally undermined when the product became the first solar module worldwide to pass the large hailstone test. The test was conducted by Institute Cetecom ICT Services.

Hailstones with a diameter of 55mm hit the panel at an impact force 23 times stronger than in the standard hail stone test outlined by Standard IEC 61215 Ed.2. The result was astonishing and reassuring. “We were not able to find any effects at the examination of the module,” confirms Wilfried Latz, Head of the photovoltaic laboratory at Cetecom ICT Services GmbH. This suggests that the module can withstand strong winds, snow load and above all generates high yields even in light conditions affected by fog, rain and clouds. A salt spray as well as an ammonia test completes the number of tests where the Conergy modules have proven to resist the most adverse conditions and remain unscathed.

Longevity and robust design are two very important facts since a solar installation needs to last at least for 20 years or even longer and provide the investor with consistently high performance and yield. Of course, efficiency is another key characteristic of a high-quality module. Here, the test and quality seal ‘PV+Test’ of TUV Rhineland and Solarpraxis AG attest the PowerPlus modules one of the highest efficiencies so that the investor can not only rely on robust design but also on high yields. Still not enough: The solar exports are currently integrating the new so-called ‘OneStep Selective Emitter’ technology in the Conergy module factory. This technology will enable increases in efficiency of up to 0.5 percentage points in the cells and modules and a further expansion of Conergy’s manufacturing capacities at the same time

“Our factory is one of the most modern solar factories of the world already today. But we don’t want to rest on our laurels. That’s why we are already looking ahead to the technologies of tomorrow─and using them in our production facilities. That way, we increase our cell efficiency, minimise scrap and increase output. A genuine technological leap for us,” says Mathias Kamolz, Factory Manager and Technical Director of the solar factory.

Antje Stephan is Senior Manager Public Relations at Conergy AG (www.conergy-group.com), Hamburg, Germany. Stephan has a degree in Languages & Literature (French, English, Spanish) and a degree in Economics.