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A New Era of GCL Cast Mono Silicon

2019-03-27   

On March 8, the 2019 High-efficiency Polycrystalline and PV Technology and Product Seminar took place in Suzhou, an event co-organized by Suzhou PV Industry Association, Canadian Solar Inc., and GCL-Poly Energy Holdings Limited under the auspices of Jiangsu PV Industry Association. Dr. Wan Yuepeng, CTO of GCL-Poly, delivered a keynote speech entitled "A New Era of Application of Cast Technology – Cast Mono silicon" at the seminar.
The following is the main thrust of Dr. Wan's speech:

 With the technological advancement of GCL, the company’s cast mono wafers have been accepted by users as competitive products, with a growing market share in recent years.
 The modules using its cast mono wafers have no notable surface defect.
 The difference between the production efficiency of GCL Mono PERC cells and that of mono silicon cells using the Czochralski (Cz) process on the same production line is less than 0.3%.
 The power difference between a 72-cell GCL Mono PERC cells module and a 72-cell Cz module is less than 5Wp.
 Light and elevated Temperature Induced Degradation (LeTID) of GCL Mono PERC cells and modules is lower than that of Cz cells and modules manufactured on the same production line.
 Cast mono wafers have an oxygen content of less than 6 ppma, significantly lower than that of Cz monocrystalline wafers.
 The resistivity of cast mono wafers is reduced to a narrower range, which improves the efficiency of PERC cells.
 Compared with cells with round corners, cast mono wafers are more suitable for shingled solar cell modules.
 Cast mono wafers have a lower carbon footprint and are more environmentally friendly.

The following are the shorthand notes of the speech:
Distinguished leaders, guests, and colleagues,
It is an honor to present this report on innovations related to cast mono silicon. I believe that the PV market has entered a cast mono dominated era. The reasons are twofold.

First, ingot casting as a crystal growth technology was mostly used to manufacture multicrystalline products in the past. But this technology has advanced significantly and will continue to advance. It can be used to manufacture both multi and mono products. Second, GCL mono silicon research and development started very early. In fact, R&D of the cast mono technology started as early as the 1970s. As of 2011, there were a small number of cast mono products in the market, but they were crowded out by high-efficiency multi products in just one year or so. Therefore, the application of cast mono has come to a new era today.

Let's take a brief look at the evolution of cast mono technology at GCL. I hope my report will shed some light on the new trends in the application of cast mono technology. Year 2011 was the heyday of cast mono silicon. GCL, LDK Solar, JA Solar, and ReneSola launched their first-generation cast mono wafers and modules. But for various reasons, these products failed to take off. Despite this, GCL continued to invest in the R&D of ingot casting technology. The company launched its second-generation cast mono wafers in 2013 and the third-generation wafers “GCL-Poly Mono G3” in 2017. The third generation performs quite well in the market. Since we lowered its price, its penetration rate has gradually grown. By the end of 2018, several customers had started mass production of products using GCL-Poly Mono G3. Therefore, I believe that the application of cast mono wafers has come to a new era, and the penetration of cast mono wafers will rise very quickly.

Now, you may ask the question of why the first-generation cast mono wafers failed to take off. It is a good question to clarify. First, they had notable surface defects, which in turn affected market acceptance; second, they were not efficient enough. These two problems were the main reasons for the failure of first-generation cast mono wafers. In the past few years, the R&D team of GCL has focused on decreasing the surface defects and improving the efficiency of mono silicon in order to increase the penetration of cast mono products.

The primary concern of our customers is how our wafers will perform in the market and whether they are cost-effective. It should be pointed out that GCL-Poly Mono G3 is either 100% monosilicon or contains no more than 1% of other crystalline materials. Let's take a look at the diagram of GCL-Poly Mono G3 on the lower right side. As we can see, the color deviation area takes up less than 1% of the total area of the wafer, which is acceptable for GCL-Poly Mono G3.
The surface defect of a GCL-Poly Mono G3 module is tiny and can only been seen from a very close distance. The previous surface quality problem has been resolved completely.

As for efficiency, due to the improvement of our cast mono silicon technology, the area of low minority carrier lifetime is greatly reduced, and we now can detect dislocation through PL. Therefore, GCL-Poly Mono G3 products, with a lower dislocation density, have improved minority carrier lifetime.

These are data of the products of our three customers using GCL-Poly Mono G3. There are two sets of efficiency data from Customer A. One data set is before surface defect selection. The average efficiency is 21.7%, and there is almost no “low efficiency tail”. The other data set is after wafers containing a high proportion of smaller grains are sorted out. The average efficiency after sorting is 21.8% and there is no "low efficient tailing". The efficiency of SE cells of Customer B is 21.95%, only 0.25% below that of CZ mono cells manufactured on the same production line. Customer C uses the black silicon texturing process to manufacture GCL-Poly Mono G3. The efficiency is 21.7%, and models manufactured through this process have the same power output as those using the alkaline texturing process.

GCL-Poly Mono G3 also has a lower oxygen content and lower light-induced degradation. Its oxygen content is only half of Cz mono wafers’. According to the data, GCL-Poly Mono G3 performs very well in LeTID.

As we can see from the power distribution diagrams, the power difference between a 72-cell GCL-Poly Mono module and a 72-cell Cz mono module can be controlled within 5 watts. In terms of EL, although GCL-Poly Mono G3 products perform less well than mono products, they perform much better than poly products.

GCL mono wafers are created in a square or rectangular shape and thus are suitable for shingled cell modules. GCL System Integration is currently trying to expand the shingled cell module business. I believe it is a smart choice. As we can see from this picture, the module looks very neat. Furthermore, the power output of a 72-cell module can reach 405 watts.

So what are the advantages of GCL-Poly Mono G3? It has lower light-induced degradation, narrower resistivity distribution, smaller carbon footprint, and lower power consumption during the crystal growth stage, and is square or rectangular shaped without chamfers.

As for reliability of modules, the cumulative installed capacity of cast mono modules from 2011 to the present has reached approximately 1 GW, most of which is installed overseas. We currently don't have sufficient data in hand, but we are building our database. The EDF has been using cast mono modules in recent years. The cumulative installed capacity of the EDF's cast mono modules has reached hundreds of megawatts.

Regarding the size of silicon wafers, I believe larger silicon wafers will be the dominant trend as larger sizes can reduce the cost of manufacturing. The sizes of silicon wafers need to be further standardized. There are too many different sizes between 156.75-158.75 mm in the market. Standardizing silicon wafer sizes is conducive to the sustainable development of the entire industry. We are advancing the standardization effort with the help of the standardization committee of China Photovoltaic Society, and planning to make the outcome an IEC standard. We hope more companies will participate in the development of the standard. Based on our market forecasts, 58.75mm wafers will become the dominant product in the market in 2019.

Many customers are concerned about the production capacity of GCL-Poly Mono G3. I can tell you with certainty that, as of the end of 2019, the total production capacity of GCL-Poly Mono G3 will reach at least 8-10GW.

There are a lot of reports in the media about the competition between mono and multi products. In fact, we should pay more attention to the competition between the ingot casting process and the Cz process. The ingot casting technology can improve the cost-effectiveness of wafers because mono silicon can increase the electrical conductivity of wafers. The development of the ingot casting technology will further reduce the cost of silicon wafers, and drive the development of N-type mono wafers for heterojunction and TOPCon cells. The industrial base of ingot casting technology such as equipment, facilities and supply chains are massive in China. At present, there are at least three or four thousand ingot casting furnaces and many people working in the industry. These are valuable resources. How can we make full use of these resources? I believe collaboration is the answer.