Just as PERC becomes synonymous with high-efficiency P-type PV cell, black silicon has returned with a vengeance. Though black silicon has been somewhat overhyped before, manufacturers are now again testing this technology to see if it can improve the performance of multi-Si cells. With the competition between mono-Si and multi-Si products moving into the high-efficiency market, debates over which manufacturing technology offers the most benefits begin to heat up as well. Industry participants are closely examining PERC and black silicon in terms of cost-performance (C/P) ratio and technological maturity. They are also looking into the potentials of the two rival processes with respect to the practicality of commercial production and capacity expansion.
The state of mono-Si market towards the end of 2015
Mono-Si technology represented the smallest share of the global PV products in 2015 on account of weakness in the European market. Not only did the production of high C/P mono-Si cells failed to reach the expected level, the overall price difference between mono-Si and multi-Si products remained large in the first half 2015. Consequently, the mono-Si demand slumped for the entire year.
In the second half of 2015, almost all mainstream mono-Si products had been squeezed out of the major regional markets. In Europe, the U.S., Japan and other parts of Asia, 270W and 275W mono-Si modules did not make the top five products by market share during this period.
The only market that has given mono-Si products a fighting chance is China as leading domestic wafer manufacturer Longi and its subsidiary Lerri Solar strive to prop up the market. Their efforts have been aided by the “Top Runner” program that was initiated by the country’s National Energy Administration to promote the use of high-efficiency solutions. Hence, there will be renewed market share competition between mono-Si and multi-Si products in China this year.
Figure 1: The distribution of mainstream PV products in major regional markets in the second half of 2015
Source: Customs data report from EnergyTrend
A mono-Si module with the same amount of solar surface area as its multi-Si counterpart will have higher wattage output and therefore can help reduce the average cost of building a PV power plant. To increase their market shares, mono-Si product manufacturers continue to make the case that their utility-scale systems produce more electricity than the multi-Si competitions.
Lerri Solar’s mainstream mono-Si modules have generated a buzz in the market since last year because they are only priced RMB 0.1/W higher than their multi-Si counterparts. The wafer and cell markets have also seen prices of mono-Si and multi-Si products intersect. On the whole, mono-Si products managed to have some market successes in China at the turn of 2015 and 2016 due to their broad adoption by the country’s large-scale PV power plants.
Figure 2: Price trends of mono-Si and multi-Si cells
Source: EnergyTrend’s monthly price report
First-tier Chinese manufacturers have continued to increase the share of mono-Si products in their respective shipments. As a result, the mono-Si wafer market have quickly shifted from oversupply to shortage over a short period of time. Major suppliers such as Longi and Zhonghuan in response have expanded their capacities and raised prices. After the Chinese New Year, the average price of mono-Si wafers was again above US$0.9/W. Though mono-Si demand has been strong in China, prices of multi-Si wafers and cells have fallen sharply since March due to the slowdown at the end market. This adds another variable to the competition as multi-Si products are again being sold at a lower price.
PERC and black silicon establish their places the competing technology roadmaps
The rivalry between mono-Si and multi-Si, which began in the mainstream product market, has gradually extended to the market for advanced, high-efficiency solutions. In the case of PERC cells, both mono-Si and multi-Si products exist on the market, though the former have an edge in efficiency. Black silicon on the other hand can help P-type multi-Si cells break into the high-efficiency market by reducing the cost and increasing the efficiency of diamond-wire sawn multi-Si wafers.
Mono-Si and multi-Si offers different paths for PERC
Volume production of PERC cells began in the end of 2013, and since then manufacturers worldwide have quickly expanded their capacities for this technology. The global PERC capacity is forecast to reach 14GW, a huge increase from the 2.5GW in 2014. However, the industry has yet to reach a conclusion on whether this technology will be primarily used in the mono-Si or the multi-Si manufacturing.
PERC works better on mono-Si products in terms of increasing conversion efficiency, but mono-Si PERC cells suffer a higher rate of light-induced degradation (LID) than their multi-Si counterparts. Cost-wise, there is not much difference between mono-Si and multi-Si PERC cells. Manufacturers’ decision will therefore be based on the price differences between cells and modules as well as the demand in the downstream market.
Table 1: Price comparison of different modules
Source: Data from EnergyTrend
In the PV system market, the price competition between mono-Si and multi-Si modules remains close. With similar costs, a module using mono-Si PERC cells made with M2-size wafers will have a 10W output advantage over a multi-Si PERC module. On the whole, mono-Si modules can obtain better prices in the system market, whereas multi-Si products are somewhat lackluster when it comes to cost-performance.
However, most manufacturers have higher multi-Si capacities that will need to be consumed by the demand from various market channels. For this reason, module suppliers such as Hanwha Q-Cells and REC continue to promote multi-Si PERC products, ensuring that there is a certain percentage of multi-Si products in the PERC market.
Figure 3: Distribution of mono-Si and multi-Si PERC products, Taiwan and worldwide
Source: Data from EnergyTrend
Though the overall PERC capacity has grown, the technology still faces a host of challenges. In addition to PERC products having LID, the related equipment takes a long time to set up, calibrate and maintain. The total shipments of PERC products in 2015 therefore only reached 1GW. EnergyTrend expects more PERC products to enter the mainstream market in the second half of 2016, such as 290~300W modules priced around US$0.57~0.6/W. Besides the recent introduction of high C/P products, equipment providers including Centrotherm and Despatch are expected to put forth effective solutions to the LID problem. Nonetheless, multi-Si PERC products still have some way to go in achieving competitiveness in cost and efficiency. The industry is therefore also looking at other ways to improve PV cells, including diamond-sawn multi-Si wafers and black silicon.
Dry vs. wet etching in the black silicon process
In the past year, mono-Si wafer manufacturers managed to significantly cut down their wafer-slicing costs by switching from the standard slurry sawing process to the diamond-wire sawing method. Multi-Si wafer manufacturers are also considering adopting diamond-wire sawing to stay competitive. Hence, this manufacturing technique is now seeing a resurgence in interests.
Past R&D on using diamond wires to cut multi-Si wafers have not been successful. The process have resulted in undesirable features on wafers, including highly reflective surface texture and visible saw marks. Since these problems affect a cell’s conversion efficiency, manufacturers are working on ways to overcome them. The black silicon process, which involves etching nanoscale craters onto the wafer’s surface, can make the surface of a diamond-sawn multi-Si wafer more uniformed and very low-reflective. Currently R&D efforts on black silicon reveal that this process dramatically increases the light absorption and conversion efficiency of multi-Si cells. It also improves the appearance of diamond-sawn wafers. In sum, black silicon together with diamond-wire sawing offers a possible new way of reducing the cost of wafer production.
Currently, there are two processes for creating black silicon cells: reactive ion etching (RIE) and metal catalyzed chemical etching (MCCE). The former treatment is sometimes referred to as “dry etching,” while the latter is also known as “wet etching.”
Currently, RIE is more popular in the market as this method offers larger efficiency increases. The high cost of RIE equipment, on the other hand, effectively prevents smaller operators from entering the field. The machines for MCCE are much cheaper, but the technology has yet to reach maturity. Some of the unresolved issues surrounding wet etching includes uneven color on wafers, lower conversion efficiency rate than RIE and liquid wastes that are difficult to recycle.
Most importantly, the industry still has doubts about the effectiveness of black silicon at the cell or wafer level. Most manufacturers are waiting for leaders such as JA Solar and Canadian Solar make the first move on adopting this method before deciding if they will follow suit. Compared with the rapid capacity growth of PERC cells in the past few years, the black silicon technology will see a much slower capacity expansion during 2016~2017.
P-type cells to lead the mainstream market
To maintain high capacity utilization and reap greater profits, PV manufacturers in general are focusing more on sources of demand in the high-efficiency market, such as China’s Top Runner program and other rooftop projects. For this reason, they will continue to optimize wafer production, conductive paste production and screen printing. At the same time, they will keep working on PERC and black silicon to improve the conversion efficiency rates of their products. The market on the whole will see more entrants and become more mature on account of these developments.
Looking ahead, the global market share of mono-Si products is forecast to gradually expand with each passing year from 2016. China, in particular, will be a powerful mono-Si demand driver. Manufacturers will begin to use their expanded PERC capacities in the second half of this year. Due to their high C/P ratios, PERC products will check and delay the market share growth of N-type cells. According to EnergyTrend, the market share of N-type products will remain around 5% until 2018; a large increase is not expected.
To hold off the advance of mono-Si technology, multi-Si cell manufacturers are going to adopt black silicon to improve the efficiency of their products. The global production capacity of this technology is projected to arrive at just 1GW by the end of 2016. The industry’s interest in black silicon has been reignited this year, and the buzz around related manufacturing processes will grow as the overall quality of diamond-wire sawn multi-Si wafers stabilizes.