The weekend read: Coating puts busbars back in the game

From pv magazine November edition

pv magazine: How do you best describe Selectively Coated Ribbons (SCR) technology?

Toralf Eggert (TE): It is an extension of an idea that Heraeus Photovoltaics came up with more than one year ago, when we wanted to broaden our product portfolio besides our pastes – which are our standard product.

So, it is a part of the ‘Beyond Paste’ strategy?

TE: It is a part of this strategy. But our idea was that we needed a partner that could really bring this into the market. As we didn’t want to start producing ribbons, we selected the best possible partner among the ribbon manufacturers, and this is Ulbrich.

Why then is it attractive to Ulbrich?

Peter Berghofer (PB): We have been in the ribbon business for what I think is the longest [period of time], which is 25-30 years. During that time, we have introduced a lot of good ideas when it comes to ribbon.

When we heard for the first time the potential of this product and saw what it could do, we decided to go forward with it. We immediately identified it is a game changing technology – if it worked.

Now we are in the position to tell everyone that it works. It has been proven in manufacturing, and on the module level.

But that phrase ‘game changer’ really does get used a lot. What does it actually mean in this instance?

PB: It is relatively easy. The customer gets more power, and doesn’t need to change anything. There is no investment in new technologies, no loss or change in production on the production lines, and the product itself is not dramatically more expensive than a standard ribbon. Liquidity is always an issue and new investment is always an issue [in module manufacturing], and investment in new technology is also an issue, so if a customer is able to increase the module power simply by changing one of the raw materials, that’s a no brainer. There is not a load of cost involved, and no impact on reliability.

What kind of boost does it deliver?

PB: In the trials [passing both TCT 400 and 240 kWh/m² UV damp heat] comparing a reference product and our new SCR technology, with a pilot customer in Germany, we saw an average of 1.9 W per module, with some modules showing up to 2.2 W.

How does the white coating deliver that?

PB: It is internal reflection.

TE: The white coating reflects the sun diffusely. This promotes the internal reflection of the sunlight at any angle of incidence.

So, the sunlight hits the ribbon and is deflected off the ribbon on the cell surface?

TE: We see two different mechanisms at work in the SCR. Sunlight that hits the side walls of the ribbon is reflected directly onto the cell. On the other hand, sunlight that hits the front face of the ribbon is reflected indirectly. After its first reflection from the SCR it will hit the glass surface from the inside and from there on it will be reflected back onto the cell. These two mechanisms add up and help us to increase the efficiency of the module. At another pilot customer we have seen gains of up to 2.4 W and that is only on pilot production. Once we have stabilized the processes and have it up and running in high volume production, we assume we can enhance the design and increase the power gain even further.

Is it best suited to a particular type of cell? What is the optimal technology for application?

TE: The SCR is compatible with most cell technologies. Its advantage grows with cells of high efficiency. We began working from the existing standards, using four through to five busbars…

PB: Actually, even six busbars is possible. In fact, it can be used on half-cut cells and bifacial modules. There is a lot of potential in this product and we have only just started working on it. But we see a big, big potential. It can be further developed.

How does it compare to other white-laminated ribbons that have been introduced previously?

PB: The plug-and-play aspect really is the biggest difference. There were white coated ribbons that lost their color after soldering, or ones that could only be used with conductive adhesives and all the process changes that come with that. But [in production] this is really taking out the old ribbon and putting in the new one.

But can it be deployed at the same temperature of soldering and with a range of soldering technologies?

TE: It does require a slightly higher temperature, but this really doesn’t matter. We have checked with all of the available stringing types and it really does work on all of the available technologies. The major advantage compared with older versions of white colored ribbon, is that there is no yield loss. Right up to the last meter of the ribbon can be used.

PB: There are no synchronization losses.

How was the coating itself developed?

TE: It was developed by Heraeus working with a partner and it is part of the IP that we have.

PB: We can simply say that it is highly reflective and temperature stable but nothing more than that.

How does it work on a cost basis versus conventional ribbons?

PB: We’re still working on that – optimizing the costs. The target is, of course, to be as cost efficient as possible for our customers. There might be a slight increase price wise, but not as much as the benefit for the customer – that is for sure.

TE: We have worked very hard on the ‘customer cost of ownership’ benefit. For sure there has to be a benefit for the customer for efficiency on one side, and then there is additional length, because we reduce the actual density of the ribbon by about 5%. That results in there being additional length for the same 5 kg [of feedstock]. These are two effects for the customer. For sure we want to gain some margin here, but the benefit for the customer is of highest importance.

How is the environment now for introducing a new product like this, because we know that there is a pretty big squeeze on the manufacturers with falling module prices?

PB: I have honestly been pleasantly surprised by the feedback. We have launched quite a few new products over the past few years. But especially for those customers with established lines, getting an additional 2 W out without any additional investment, then the question is, “why wouldn’t you take it?”

The response from the technical people here at EU PVSEC has been great. Even from the first press release we received a number of enquiries and people are positive about a solution like this.

TE: The appetite is there and it is not only out of Europe. We already have the first requests from Asia. The reason is that customers are really looking for new solutions with different colors, even from purely a design perspective. So, we are working on different solutions and things like black ribbons even could be a next generation.

What then are the next steps?

TE: The next one will be a full production line up and running early next year, and then we will see what the expansion will look like – depending on customer demand.

Interview with Jonathan Gifford