Coolback interview: Lower temperature, higher performance


This is an extended version of an article that appeared in the May edition of pv magazine global

pv magazine: Can you give me a quick introduction to Coolback?

Coolback is an application for PV modules, replacing the frame and the backsheet. It delivers strength and cooling to the module.

Simon Meijer: “Our target in designing … was not to raise the cost per watt peak.”

Image: Coolback

What is the key advantage?

First, the advantage of the cooling is that it delivers an increase in power output – at an annual rate of 3-5%.

And that is power output?

That’s right.

Does that mean that the effect is amplified in hotter regions?

The backsheet works in all conditions, because PV modules reach [an operating temperature] above 60°C, even in Germany. But of course there is increased value at higher irradiation and temperature areas – where the heat losses are major so the contribution of Coolback is bigger. The benefit is accelerated at higher temperatures.

And for longer periods of the day, I imagine…

Of course. And when applied on a double axis tracker then there is more sun load on the module, so the effect of Coolback is also bigger.

So, how does the technology itself work?

We actually subtract lead the heat from the cells to the backside of the modules. From there, we dissipate the heat to the surrounding air by convection cooling and radiation cooling.

What is the hardware itself?

It is a heat sink, but it’s a very specific heat sink. There were heat sinks for PV cooling in the 1980s – heavy, thick, aluminum plates. What we designed is something that is very thin, the same weight of a standard frame. And it is not only a heat sink, it has been designed as a weight bearing structure of the module, the structure delivers strength.

You can see it as a heat sink in a similar way to an egg box. This means there is a lot of surface for convection cooling and the shaping has been designed to give the maximum strength to the module.

Coolback involves replacing the conventional frame and the backsheet. How does it compare on a cost basis?

The total cost of bill of materials (BOM) remains the same, it is equal [to conventional module BOM]. That is because the cost of the conventional frame and backsheet together is equal to Coolback.

That approach seems to fit one certain theory of innovation within PV, that innovations only really work if they have no impact on a cost basis, but can boost performance. Was that your intention?

Exactly. Our target in designing a product and production methods was to not raise the cost per Watt peak (Wp). That is what we managed to do. And at the same time, we were able to increase the power output. The other additional advantage is that we deliver an increase on module lifetime. The effect of that is not immediately visible but will be more apparent after some time. That is because the stiffer module and the lower [operating] temperature will reduce degradation. This is something that is difficult to test, as it is mainly done in failure testing for the IEC certification, but we will look at some effects on lifetime as well. The general understanding is that if the temperature on the module is 10°C lower, always and at every thermal cycle, you will improve the module lifetime.

Every module innovation must also last at least 25 years. How can you convince module makers or more importantly investors?

We just passed the same IEC testing as every backsheet has to do. The other thing is that we did outdoor testing for 2 years – and this is something that we are going to continue to do.

What type of outdoor testing have you been doing?

We have been conducting outdoor testing in southern Spain over the last two years – primarily to test the way we connect the Coolback structure to the backsheet. And outdoor testing is also done at several hot locations to measure the performance impacts. These sites include Qatar, southern Spain and Milan for tracker applications, and soon also in Morocco and India.

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Improving the output and lifetime of PV through cost effective cooling

What can you tell me about the company Coolback itself?

We are, I suppose you can say, an ‘extended startup’. We started work around seven to eight years ago. Originally, we were working on optics connected to solar PV – low concentration PV. Within a few years we produced a low-concentration PV system that functioned technically. However, it involved cutting solar cells into smaller parts while, at that time, cell prices were dropping rapidly; this evaporated our business case. Everything we had learned – especially cooling properties – was rolled into a new project three years ago. From that point on, we developed Coolback.

What has been the reaction from module makers – they are a notoriously conservative bunch?

There has been big development over the last seven years or so. Even two or three years ago, almost everyone was focused on commodity production, lowest cost and prices. But in the last two years there has been a recognition that innovation and differentiation is key to survival. Coolback actually fits into that trend, so we are welcomed by the module manufacturers.

The other thing is that unsubsidized solar is becoming more-and-more interesting. People have started to educate themselves that kWh is more important than kWp. There we also fit perfectly. We don’t change the Wp of the module, obviously at flash test that doesn’t change, but in real world applications the additional output is just money. The role of asset managers and EPCs is getting bigger and bigger. They increasingly dictate what should be delivered and we also ride that wave.

I imagine you are also talking with EPCs about using Coolback-integrated modules.

Of course. And the EPCs have to be convinced of the technology from a safety point of view. As soon as that is delivered, they are all in for extra output and additional lifetime.

On the BoS front, in terms of the racking and ground mounts. If the module is constructed slightly differently, then does that have an impact?

Actually the frame, as we know it in solar modules, has not developed at any point in the last 40 years – they only became thinner to reduce the material cost.

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But they still comprise a considerable chunk of a module’s price.

Exactly, and that is quite surprising to see how long a big amount of money has been spent on something quite stupid. There is no technology, nor is there any intelligence in the frame. That was our connecting point to say, ‘we can use this budget from the BoM [bill of materials] to make something quite different. There can be much more functionality integrated [into the frame]’.

But can modules using Coolback be racked or mounted the same way as conventional modules?

First of all, there is the standard way that normal glass-glass modules are mounted, using the clamps on the rim. That can be easily used for Coolback modules. We are also developing for the market a mounting system that is attached to the backside of the module, instead of to the rim. We have the entire backside of the module available as an attachment point, and we can make use of that.

If you look at how pressure at the points of attachment influences things, like pressure on the module, it is very interesting to see how you can make beneficial use of that.

And from the looks of things, the Coolback structure is comparatively solid and robust. Does that mean there is more to play with in terms of mounting?

There are more points of attachment. There is additional rigidity. But by comparison to framed modules, where the frame adds to the module’s height when they are stacked together, we have designed our structure so that the modules can be nested together. Coolback has a more triangular form, two modules can be stacked together [for transportation] at the same height as a single 40mm framed module. This means that we reduce transport costs by around 30%.

Does that also assist with damage in transportation?

Of course, you have to take care during transport. Plastic corners in the packaging are needed to pack the modules really nicely. But you can fit more modules in the sea container and also in the ‘last leg’ – the truck that takes the modules to the site. All transport volumes are lower.

Looking to manufacturing, there has been some evolution in the junction box (JB) space – from single to split and different placement of the JB. How compatible is Coolback to these kinds of innovations?

Because the structure of Coolback is made from more profiles, we can just change the number of profiles that we attach to the backside of the module.

 What do you mean, more profiles?

Coolback is not one big plate, it is composed of different segments. The number of segments makes for easy application to a 60-cell or a 72-cell module. But it also makes the placement of the junction box easy – because you place the profiles around the JB. It is a modular design.

The module assembly then. I understand that there is specific production equipment required. What can you tell me about that?

I suppose you can say that Coolback is composed of two parts: The backsheet – which is laminated during production and uses exactly the same operating procedure, and Coolback profiles- which is integrated at the station where you normally do the framing. A different machine is required for this process, but we provide that machine.

How do you it?

We provide the machinery in partnership with machine builders. We used very specialized knowledge when designing that assembly machine.

It can be first put in operation as a bypass to the framing station, as an alternative. Then at one point, it can simply replace the framing machine that is used today.

And are the tools in operation in production lines today?

We are in the final stages of development and have tested it as prototype.

Are there manufacturers actually deploying Coolback today?

Yes! We have four that are showing Coolback integrated modules during Intersolar Europe 2019. Two of them already make use of the complete production procedure – which means that there is a certified procedure and module.

So if these manufacturers are not using the full automated production tool, how are they integrating Coolback in their production?

At the moment, there is a semi-automated way to do the assembly. This summer, we will deliver a fully-automated system for production – which will operate at a speed of 90 modules per hour.

For Coolback Company, what is your business strategy? Are you purely a materials supplier or will you license the technology?

To start with and to ensure the highest level of quality, we will provide everything – the Coolback structure, adhesive between the Coolback and the backsheet, and the assembly equipment. We in-source some of it, some it we produce ourselves.

If a bigger producer would like to do some of the production itself, then we will supply the specifications and makes sure that it would pass certification standards. In particular, this strategy works for China, where producers like to stick with their own backsheet supplier.

Are you worried about ‘copy cats’?

Yes we are. Of course, it’s a big issue. We’ve had long discussions about how to deal with that. There are several ways to do it. First of all, to avoid any copying would mean to stay out of certain countries all together. That is actually not an option because then you miss the market. The other option is to say that we have to deliver a product at a price that is so low and so competitive that it wouldn’t be a significant gain to actually copy the technology. We are looking for volume rather than niche manufacturing, so that will lower the incentive to copy. We also are staying ahead of product development. Even though we are introducing Coolback now, we have 2.0 in development and in certification for release next year. We will have some tricks in our product and assembly machine to ensure that the two are connected, and fake materials can’t be used. And we are also looking for partnerships with the big manufacturers so they too would have something to lose if there is copying.

Finally, we have several patents and will enforce them when needed. The market is so big that we will probably not be the only ones to sell the product in the end. In some way, I hope there are some copies, as it would be a big compliment to our development.

Am I right in understanding that this is a ‘made in Holland’ innovation?

Not really. The development first started in the Middle East. We have development and a workforce from all over the world. The Netherlands is a good logistical point and the entrepreneurial basis is good. But we are already on a good international footing.

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