As the COO for Stiesdal, Peder Nickelsen is a trusted advisor to Cotes and many otherin the wind energy industry. We asked Peder why he thinks it is important to have a good dry-air strategy inside a wind turbine and throughout the entire turbine lifecycle.


Benjamin: Thank you for taking the time to meet with us Peder and for agreeing to share some of your experience and insights. Can you briefly introduce yourself and what you do? 

Peder: My name is Peder Nickelsen and I’ve been in the wind industry for more than 30 years. I´m currently employed at Stiesdal A/S as COO where I´m heading the various activities we have going on. At the moment we are looking into a relatively wide portfolio of projects focused on advancing sustainable energy solutions and technologies, things like floating foundations for offshore wind turbines, thermal storage technologies, and we are also looking into Power-to-X and pyrolysis. 

Benjamin: Sounds like sustainable energy solutions is a theme in your extensive career. 

Peder: Yes, I have been very much involved in the development of the offshore wind industry where I´ve had the design responsibility for many wind turbines early on in the growth of the wind industry. The journey has been positive, and I have seen this industry grow quite dramatically since I did my very first turbine back in 1998, the very same turbines, I´m quite proud to see, are still operating outside Copenhagen today. 

Benjamin: That is a long time to have an operational offshore wind turbine. Does humidity not cause issues inside the wind turbines? After all, steel and water are not the best of friends. 

Peder: I think overall to control the humidity is a very important thing in relation to the operational lifetime, turbine design and the associated OPEX costs. It´s actually not only an offshore thing, it's also relevant for onshore turbines where the turbines are exposed to humid climatic conditions like we for instance see here in Denmark. 

However, the overall goal is to make sure that the design is matching the kind of humidity the various components inside the wind turbine is exposed to, which is why it´s important to have a dry-air strategy. Especially if you are working with a low corrosion classification inside the turbine. This is mainly to avoid high OPEX costs over the lifetime of the wind turbine and also to avoid the sort of unforeseen issues or unforeseen breakdowns caused by excess humidity.

These breakdowns can of course be rather costly because it is normally quite expensive to repair issues with corrosion. It's not only corrosion issues on steel, but it can also be corrosion issues in relation to the electrical systems which can lead to even main component failures if you have corrosion for instance inside a generator or a transformer. 


Benjamin: One might be excused for thinking that humidity is only an offshore problem, but it sounds like humidity is a general issue in wind turbines. 

Peder: Yes, I think there are potentially humidity issues or challenges on both offshore and onshore turbines, partly because onshore turbines are also exposed to excessive humidity.  But again, I think the overall challenge is to make sure that the design is matching the requirements for the turbine and for instance for the offshore application you would normally have a dehumidifier installed that basically ensures that there is only a certain humidity in the air and that has a huge upside on the corrosion robustness of the turbine over time. 

Benjamin: Earlier on you mentioned the importance of having a dry-air strategy. What is a dry-air strategy and how is it different to choosing a corrosion class for the wind turbine? 

Peder: A dry-air strategy is how you plan to prevent and negate the harmful effects of humidity inside your wind turbine. Choosing a corrosion class for your wind turbine is one part of the strategy. However, in my experience and to my best knowledge, installing an adsorption dehumidifier is still what is widely used in the industry with the best results and if done right it will allow you to use more standard and cheaper components inside the turbine and reduce the corrosion class.

If you don't have a dry-air strategy you need to design for quite severe conditions or design for the worst-case scenario, which could even be what is called a C5M marine environment and that would inevitably result in a significantly higher cost of the component. There would also be a significant risk that without dry air, even a small scratch in the surface protection of the component could lead to corrosion issues. If you have a dry-air strategy then this risk is very much mitigated and thereby your design is much more robust, because small scratches would occur over the lifetime of the product. 


Benjamin: Now that you mention wind turbine lifetime when you look at how the cost of wind energy has decreased over the years, do you think it is possible to reduce OPEX costs even further than what is possible today? 

Peder: Yes, lower OPEX costs are possible. I think a dry-air strategy is one of the enablers to have a low cost of energy from the wind turbines, especially the offshore turbines. It is also an enabler to achieve more foreseeable OPEX costs over the years and not to run into unforeseen warranty costs. I think the overall benefit would be that the power from the wind turbines is getting more reliable but also the secondary effect is that the bankability of the wind turbine is becoming higher and thereby there is less concern for investment bankers to invest in the offshore wind turbines.  

Benjamin: We see a lot of investment in the wind energy sector now, so is bankability really still a hurdle? 

Peder: Yes, the way I see it is that the bankability of wind turbines also includes avoiding excessive downtime, meaning downtime in addition to what you have planned for. And here you need to make sure that you have a corrosion protection strategy that could employ dehumidifiers to avoid unwanted and unplanned failures and downtime.  

Although, bankability starts long before the wind turbine produces its first Watt of electricity. Even before the turbine is installed some turbine components may have a long transit time, which can be many months or even a couple of years. With components in transit, it is normally a good investment to also have control of the humidity in order to avoid potential corrosion or free water forming inside the turbine or the turbine component during transit for prolonged transit periods. 

Benjamin: Now we have talked about offshore wind turbines, but we have not mentioned the new kid on the block, floating foundations. Should you have a different dry-air strategy for floating foundations? 

Peder: No, I don’t think there is any significant difference between the importance of a dehumidifier on a floating foundation compared to fixed foundations. However, most of the floating projects would normally be for very deep waters or relatively deep waters where it is not feasible to have a fixed foundation and where the wind resource is very high. These remote locations are harsh environments for wind turbines so the corrosion requirements for the floating market segment would probably be higher and thereby the necessity for having control of the humidity is also very high for this market. 

Benjamin: Is a dehumidifier really the best way to dry the inside of a wind turbine

Peder: Well, as I mentioned before, there are some obvious alternatives to a dry-air strategy for securing the corrosion protection of a turbine. However, over the years we have been testing a number of alternatives and my personal belief is that a dry-air strategy has come to stay, at least when you have a relatively enclosed environment, because it has proven to be very effective, robust, and also a relatively speaking cheap way of securing the environment inside a wind turbine if you consider the cost of downtime and replacing expensive electrical equipment that fails due to uncontrolled humidity. Another extremely effective dry-air strategy is to desalt the air for an offshore application. Desalting combined with dehumidifying provides the best results possible. 

If you experience issues with humidity inside your turbine, Cotes offers a FREE humidity test kit for you to test the levels of relative humidity inside your turbine.

Order a FREE Humidity Test Kit




Stiesdal A/S is headquartered in Odense and has locations in Give and Copenhagen. The company operates four subsidiaries, each with a focus on its own green technology: Stiesdal Offshore Technologies has developed the modular floating offshore wind turbine foundation Tetra, which can be produced faster and cheaper than other solutions on the market. Stiesdal Storage Technologies has developed the energy storage solution GridScale, which can store electricity in the form of heat in crushed stone. The solution offers longer storage time than lithium-ion batteries, and an agreement has been entered into with the Danish energy group Andel to install the first demo project in Rødby, Denmark, in 2022. Stiesdal PtX Technologies has developed the hydrogen technology HydroGen, which is a new type of electrolysis system that can convert electricity to hydrogen cheaper than other electrolysis technologies on the market. The first demo project is expected to be built in early 2022. Stiesdal Fuel Technologies has developed the SkyClean technology, which can produce CO2-negative fuel for aircraft. This is done through pyrolysis where biomass is converted into biofuel for air transport while CO2 is captured and stored from the atmosphere.