Webinar Q&A: The future of back contact technology


Hugo Schoot (left), Business director at Endurans Solar, and Bram Verschoor, CCO at Eurotron.

Can IBC/MWT/CBS (back-contact) modules compete with bifacial PERC technology? Because IBC/MWT/CBS does not have bifacial capability?

Hugo Schoot: Typically, bifacial modules are ground-mounted and installed 1m+ from the ground (often on trackers) to enable bifacial energy yield gains of 8-12%. Back-contact modules find their application primarily in rooftop installations, where they can leverage their superior power density and aesthetics. So, in that sense there is no direct competition. It is not likely that rooftop installations will adapt large shares of bifacial modules because of minimal bifacial gains and weight reasons. However, we do foresee that in the future, as the cell cost-down roadmap progresses, back-contact modules will increasingly be deployed in the ground-mounted segment too. Depending on ground albedo conditions we believe that due to the lower resistive losses, lower NOCT and reflective gains from the CBS, back-contact modules will be able to compete with bifacial modules in a significant share of the ground-mount market too.

Over 100MW of modules has already been seized due to forced labor concerns in China. This has means hundreds of modules that were scheduled to be delivered after the seizure are still sitting offshore. The duty lawsuit on other countries than China threatens to delay shipments of foreign built PV panels. Is your solution easier to scale here?

Forced labor accusations heavily impact the global PV supply chain. Currently, the industry lacks transparency in the upstream segments to ban and prove forced labor is no longer present. The lack of supply chain transparency is valid for almost every crystalline silicon PV wafer produced today. As our solution also depends on crystalline silicon PV wafers we find ourselves in the same difficult situation. Only if the upstream segment opens up or new fully transparent supply chains emerge, will our customers be able to prove that there is no forced labor in their supply chain.

The market has moved to cut cells to increase voltage efficiency, as well as bifacial to achieve a higher energy yield. Is the Eurotron production line allowing a significantly faster throughput to overcome the options like bifacial or other conventional technology? Your point on touching cells are true but throughput seems the key.  What is the speed increase?

Bram Verschoor: If we look at the capacity of the back-contact production then a EuroMax90 is able to process max 5400 cells per hour, based on a 60 cell, full cell module. The total annual performance depends on the cell efficiency. 5400 cells is approximately equivalent to a maximum annual production of 290 MWp. This is based on 6.55 Wp/cell; 24/7 production and 95% uptime.

With half cells, there is a difference of 10-15% (The capacity reduces with 10-15% for half-cut cells), with a max annual production capacity of approximately 250 MWp. With tabbing/stringing the maximum capacity is approximately 100 MWp per line and half cells almost halve the production capacity. Bottom line, it is not about the capacity of a line, but about the ratio of space/production capacity and how many people are needed to run that production line. By far the most important remains the efficiency and reliability improvement.

What are your comments on the advantage of less cell stress due to heat etc. with tabbed cells?

We do quite often see on EL measurements that cells connected with tabs around the soldering site develop stress and microcracks. In addition, the cells can be damaged at the level of the tab due to stress on the radius of the bend. Both phenomena are absent in back-contact modules.

How many GW of modules have been produced with this technology?

Hugo Schoot: We estimate that close to 10 GW of modules have been produced worldwide using CBS interconnection technology by the end of this year.

Conductive back sheet requires a significant amount of metal, what increase in metal contact is that compared to standard front contact modules?

A conductive backsheet (CBS) is much thinner than a typical ribbon, so the total volume of used metal does not necessarily increase. With a CBS, it is even possible to improve the efficiency of using the metal by adapting the design to the current distribution.

Are there any new metallization technologies in IBC?

ISC Konstanz is developing a next generation ZEBRA IBC cells to replace silver metallization by copper screen printing, which will result in a huge cost reduction without compromising on module efficiency.

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Which specific back contact technologies that seem most promising for massive market adoption, is fairly even for several?

In terms of cells: There are two flavors, the interdigitated back contact (IBC) cell. Or conventional front/back contacted cells that are converted into back contacted cells though metal-wrap-through (MWT) technology. In terms of performance potential we think IBC is the most promising. However, as IBC is still relatively expensive, we do see an equal share of MWT back-contact being used in the market. The speed at which IBC takes over will depend on the speed its cost will come down.

In terms of application: At this moment we do see two segments advancing more rapidly than others. First of all the high-efficiency rooftop market, particularly in residential applications and regions where aesthetics is valued. Secondly, in the integrated PV segments like VIPV and BIPV where aesthetics and flexibility of design are key.

How will front surface charge polarization effects be mitigated over the life of the cell?

ISC Konstanz is developing a next generation ZEBRA IBC cells to replace silver metallization by copper screen printing, which will result in a huge cost reduction without compromising on module efficiency.

How do back contact products compare with the current generation of high-power modules?

Besides the bifacial gain, creating high power modules is simply a matter of using higher efficiency, larger and more cells per module. Converting the cells in these high-power modules into back contact cells via MWT, and interconnecting them with a conductive backsheet, will provide you with the same relative gain in energy output as in any module.

For example, let’s take a 605 W polymer backsheet module based on 210mm cells. Converting the cells into back contact cells via MWT and interconnecting these cells with a CBS will increase the power nameplate capacity of this module to around 640 W, adding up to a relative module efficiency increase of around 5.8%, or slightly more than 1% absolute, for PERC vs PERC-MWT.

Which are the big competitors of IBC technology and why?

Currently IBC still has a relative small market share. PERC is dominating the market but will gradually be replaced by Topcon and HJT cell technology. After that we foresee that HJ-BC and IBC will gradually take over, as shown in the ITRPV roadmap (SLIDE 8 PRESENTATION FLORIAN HAACKE)

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