Lessons learned from PV+Test


Hanwha Solar scored a good result in the test already last year, but the company wanted to test itself once again. In the overall evaluation the module earned the grade “Good (+),” thus achieving a half grade better than last year. Evaluation of the rated output had the greatest impact on the evaluation. Customers will be happy to learn that on average the modules exhibit 0.5% greater output than is indicated on the data sheet. Last year the module’s output was less than indicated on the data sheet, but within the measuring tolerance. This resulted in a clear reduction of test points at the time.
The good result this year shows that the manufacturer took the problem seriously and got a handle on it as well. Among other things, this is due to the fact that, in cooperation with TÜV Rheinland, Hanwha Solar introduced “Power Controlled” testing, explains Winfried Wahl, Senior Director Products & Marketing at Hanwha Solar. Power controlled testing involves a special program developed by TÜV Rheinland in which both the production process and the products of a particular manufacturer are subjected to testing on a regular basis. In this case TÜV checks whether the solar modules are actually capable of the output promised by the manufacturer. In the course of implementation the flashers from Hanwha Solar also received new certification, adds Wahl. This involved new calibration of all of the flashers in production using the reference from TÜV Rheinland. The deviation in the measured values between the measurement at Hanwha Solar and the measurement at TÜV now amounts to less than one percent.

The Hanwha Solar module HSL 60 Poly (HSL60P6-PB-1-255 to be precise) moved up from the overall grade of “Good” last year to “Good (+)” particularly as a result of improvement in the “nominal value power deviation” category. In addition, the “Documentation” and “Electrical Safety” categories also deserve favorable mention for the tested modules: The maximum attainable score was achieved in both cases. No surprise as the module was already able to chalk up points here last year as well.
High PID resistance
The fact that there has been little change in the design of the module since the last test can be seen, among other things, in the temperature coefficients and with regard to weak light behavior. Hanwha Solar indicates that the temperature coefficient is -0.43% per Kelvin. With a measured value of 0.425% TÜV Rheinland is able to confirm this with relative precision. There are eight to ten possible points for this value in PV+Test. The module’s weak light behavior is just as good as it was in the previous year. With 70 of 80 attainable points the module demonstrates that it provides good yield even with less irradiation.

Furthermore, as with the test last year, the module exhibits good resistance against potential induced degradation (PID). After the test the module output diminished by only 1.66%. A good value that resulted in nine of ten possible points.

However, one weak point in the module showed up already last year. In the thermal cycling test the output diminished by up to 4.7% after 200 cycles between temperatures of -40 and 85 degrees Celsius. However, it was still within IEC requirements for 200 cycles. The subsequent electroluminescence test (EL) suggested possible problems with the contact fingers and busbars on the cells. “Even with the naked eye one can see that the cell connectors are irregularly soldered in part,” says Andreas Cox, test engineer at TÜV Rheinland and responsible for PV+Test. “In my view that is clearly the weakest point in the module. The less than completely clean soldered connections could also be responsible for the loss of output after the thermal cycling test.” However, in contrast to the previous year a further 200 thermal cycling runs were unable to harm the module this year.

Uneven current flow
There were clear output losses in the damp heat test where the module is twice forced to endure 1,000 hours at 85 degrees Celsius and 85% relative humidity. After 1,000 hours output diminished by up to 2.85% (here the IEC limit is 5%), and up to an additional 3.46% after a further 1,000 hours. A visual inspection after the test revealed slight discoloration of the busbars in part and yellowing of the backsheet. A further irregularity showed up in the EL picture. Here some busbars on the same cell are brighter than others.

In the opinion of test engineer Cox, the brighter busbars indicate that the current flow over the cell is not homogeneous, but rather concentrates in certain areas. “An increase in resistance is to be assumed in the darker areas. This may be caused by irregular cell connector soldering or possible chemical reactions at the front or back metallization of the cell, triggered by the damp heat climate.”
A few points were deducted in the mechanical load test. In this case the module is first subjected to a load of 2,400 pascals, and once again with 5,400 pascals afterwards. In both cases the output remained practically stable. However, in the EL picture the TÜV examiners detected cell cracks that increased in the second run.

Weak points eliminated

All in all, however, it can be said that the module passes all of the stress tests within the standard and thus deserves the grade of Good (+). As far as the overall impression and general processing of the module is concerned, the maximum score is also earned for both component workmanship and the edge test.

In order to eliminate the weak points when it comes to the busbars Hanwha Solar completely switched over its production process to new automatic production facilities even before publication of the current test results. According to Winfried Wahl, the module tested here will be discontinued in 2015 and those modules that have already been ordered will be delivered. HSL 60 Poly will be succeeded by the HSL 60 Poly S product line, which has been manufactured since the beginning of this year. According to information provided by the manufacturer, possible weak points have been eliminated. For example, the cell connectors, which will be increased from three to four, will then be soldered fully automatically, thus further improving the temperature coefficient and weak light behavior.

“We assume that we will be able to completely eliminate possible weaknesses in the soldering process by reequipping to the newest production technology,” affirms Wahl. In addition, new innovative EVA materials and backsheets will be used in the new modules. Thus Wahl expects optimum results in the damp heat test. Through renewed participation in the PV+Test with the new product Hanwha Solar can prove whether or not module quality has been further enhanced.?
PV+Test 2.0: Hanwha Solar HSL60P6-PB-1-255

The tested solar module HSL 60 Poly from Hanwha Solar consists of 60 polycrystalline cells and has an output of 255 watts. According to the manufacturer it is used for residential buildings and on commercial rooftops and is also deployed for large outdoor projects in Europe, America, Asia and Australia. This “universal module” represents the largest-selling module from Hanwha Solar and was thus “the logical choice” for the module test developed by TÜV Rheinland and Solarpraxis. The HSL series has been on the market since April 2013. To date modules with a total output of approximately 1 GW have been sold from the HSL series. These include the Black Edition module variant with a black frame and black backsheet for rooftop installations as well as HSL 72, a module variant with 72 cells, which was designed particularly for large-scale installations. According to information provided by Hanwha Solar, the modules of the tested series are characterized by long service life. They are certified for very high wind and snow loads and resistant against the effects of potential-induced degradation (PID).
Since the first quarter of 2015 a new module generation is available with the HSL S series, which is based on the proven and widely sold HSL technology. According to information provided by Hanwha Solar, the new module series relies on a cell design with four busbars in order to achieve higher module efficiencies. In addition, Hanwha Solar recently switched to fully automated production so that constant high quality is ensured. The rated output of the 60 cell HSL S module amounts to 260 to 270 Wp, and the 72 cell modules are offered in performance classes from 305 to 315 Wp.

This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.