The days are over when silicon solar modules were only differentiated between its crystalline varieties (mono or multi) and the number of cells (60 or 72). Not only does the trend to high-efficiency cells bring more options, on top come advanced module technologies, which are now all commercially available. This is exactly one year after we published our first report on this topic, when most of these improved panels were still in the R&D or pilot production phase.
Reducing cost has been always a key driver for solar technology developments. But with solar now on the brink of competitiveness with fossil fuels, every tiny improvement counts to bring efficiency and power up, cost further down – and expand into new market segments.
While in the past, the focus was primarily on cell efficiencies to improve a solar module's output, the panel itself now contributes a larger part through advanced module technologies (which for us is about rather simple tweaks that improve output without changing the standard module design). Researchers have known these technical possibilities for many years, but only today there is the urge as well as key materials and tools available to finally move into mass production – and this happens now very rapidly.
The most simple of these advancements has basically reached its limits. The number of busbars was quickly increased in only few years from 2 to 3 in 2016, and then 4 in 2017. Now the latest commercial products often use 5-BB design. While Q Cells even already has introduced a commercial 6-BB model, experts argue how much sense this step makes, because at some point the additional shading and ribbon consumption outweigh the benefits of higher power rating.
That's why several module manufacturers are now starting to move directly to multi-busbar design, where traditional ribbon is replaced with multiple thin copper wires. This is also an elegant way of saving on silver paste for cell busbars, which are not needed anymore for this solution.
While multibusbar module production requires new and very precise cell connection tools, which are only available from very few suppliers today, the concept of half cells just needs another laser as well as more traditional cell stringers to make up for the loss in throughput (as the cells only have half size it takes twice the time to inter connect them). The power output gain per module is so impressive, that the concerns about aesthetics (half cells look a little bit like broken cells) has been set aside. In fact, who looks at the cell size in a massive multi-megawatt power plant anyway, and at some point customers will get used to the new shapes.
Who really is into real beautiful solar panels, can now choose shingle based panels, where the cells are cut in even smaller stripes, but these are assembled in roof tile style. That not only makes the panel true blue as interconnection can be moved to the backside; it also eliminates unused space between cells, resulting in higher module power ratings.
Our favorite advanced module technology is bifacial, because it makes so much sense to use the backside of a module for power production. Around 30% gain is possible depending on product and location. And it takes basically no extra effort to harvest these additional gains as high-efficiency cells are mostly naturally bifacial. Of course, a transparent back cover is needed. But here the glass industry is now having thinner solutions to address the weight issue, while the incumbent backsheet companies have woken up to defend their turf and start to offer improved transparent products as well. We have summarized the advantages and limitations of the different advanced module solutions in a table in the report on p. 47.
However, what's really great about these solutions is that they can be combined in any fashion. When we talked to Holger Neuhaus from Fraunhofer ISE about this, he came with a nice example. Taking a 5-BB module with 314 W as a reference and upgrade it to MBB would result in 318 W. Implementing only half cells would bring 6 W to 320 W. But the combination of MBB and half cells would improve the module output by about 4% absolute to 326 W. On top you could go bifacial to strongly enhance yield and chose a dual glass-based product to get a 5 year longer module performance warranty of 30 years.
The best commercial advanced panels in our survey of leading module manufacturers show several 72-cell products exceeding 400 W and 60-cell products of 330 W or more today. That's way ahead of what ITRPV forecasts. You simply want to have that!
As all these advanced module solutions are just entering the market, there is no real trend to spot, as the tables for the top commercial 60-cell and 72-cell products show (see tables p. 48 and p. 49, showing the top commercial product from each category in this report). The commercial products of the different manufacturers on offer probably are primarily a function of those tool upgrades they have been able to accomplish in-house so far. But very soon we will see most of these solutions being applied for basically all modules. First half cells + MBB + bifacial, somewhat later combined with even more advanced shingles. The only open question to us is how much market share glass will be able to take away from backsheets.
The article was originally published in the TaiyangNews Advanced Module Technology Report 2018, which was released at Renewable Energy India Expo 2018 and can be downloaded for free here.