Interview with dr. Uroš Merc: Rethinking degradation

Solar energy is gaining popularity as a source of household energy in many countries around the world. Investing in a PV system is still a bet based on trust, since the customer buys the promise of future power and waits to see if the purchase was the right choice to make. BISOL has attracted many with promoting zero degradation module BISOL Supreme™, therefore we share with you an interview with BISOL company founder dr. Uroš Merc, published in PV magazine and written by Jonathan Gifford that sheds good light on the degradation issue.

PV module making is a brutally competitive industry. And for Slovenian module maker Bisol, in business since 2004, one of the keys to success has been to remain focused on the value its products deliver to the customer. And as company founder and CEO Uroš Merc explains, in 2021 this means reimagining module degradation.

The new module series from Bisol, the Supreme series, is being promoted as being a “zero degradation module.” What was the motivation behind it?

All manufacturers are striving toward higher power, but we tried to find an alternate approach based on value for the customer. We are all, in principal, using the same cells – differences are small, mainly in quality. And while there are higher efficiency cells, n-type cells, they are more expensive and often drive manufacturers towards losses jeopardizing the value of the long-term warranties. In that sense, sticking to the mainstream’s [cell technology] highly optimized cost structure, is very important. So then, how can a module manufacturer make something different? One approach is higher power, but as everyone tends to use the same cells we just see the modules getting bigger. I think, also, there are limitations when it comes to size.

My idea was to focus on the value for the customer. I asked, “what is something that the customer would and should appreciate?” The idea came from a comparison – when you are buying a German car you never ask, “what is the horsepower degradation over a number of years?” Everything naturally degrades over time. But, from the client’s point of view there’s risk in not knowing how degradation will affect module performance. It feels like the client pays for the product twice, first for the product itself and then for degradation. In my view, when you buy a PV panel, you should buy it for a certain price and at the rated power valid for the whole warranty period.

Our principle here is that the value for the customer is in not needing to worry [about degradation]. With this new trend-setting product we don’t need to speak about degradation anymore, everything is considered in the product and in the data sheet already.

So, is it that the nameplate that you are selling at is below the nominal power output? For example, if a Supreme module has a nameplate of 370 W, then it may actually have a nominal output of 380 W.

That’s partially the case. In principle you see the same in many other module manufacturers: They claim a power output between 0 to +5 W of the rated power, but we all know that most of the time it’s closer to zero. When you have a module that has standard degradation compared to one without it, the loss in power [on the former] adds up to around 11% or more of energy yield just within the warranty period.

If we produce modules according to our higher standards, our climate chamber shows that the modules are operational for more than 100 years – and the power drop is only 25%. I believe having high quality materials is absolutely important too.

How then are you able to reduce degradation in production?

For Bisol Supreme we say “zero effective degradation” as it is effectively zero for the client. By adding a little bit of additional power in the beginning, we can allow for small degradation later on. But it’s essential to assure overall low degradation.

We can achieve this through attention to detail in module production. Highly specialized equipment upgraded by our engineers, materials that we use and test to destruction, and our unique processes combined are essential.

Our clients should be our only perspective. It is not about price, but the value of what they like. So we are not trying to make the highest power with the largest module, but the highest value for the client.