Offshore wind turbines

Avoid corrosion and mould
in offshore wind turbines

Offshore wind turbines have to be reliable — revenue depends on it. But they have to operate in environments full of corrosive airborne moisture. This means manufacturers and operators face challenges that frequently include:


  • Moist, salt-laden air entering nacelles and towers
  • Condensation and corrosion giving rise to structural, mechanical and electronics problems
  • Operational glitches and high service costs due to the effects of humidity
  • Unhealthy and unsafe working environments resulting from bacterial growth and slippery surfaces


 Airborne moisture causes corrosion

Airborne moisture is one of the major sources of operating disruption, damage to equipment and structures, and costly practical problems inside the nacelles and towers of wind turbines — especially those offshore. To our knowledge, as much as 20–25% of all breakdowns in offshore wind turbines are caused — directly or indirectly — by moisture and corrosion.

Such airborne moisture combines with acidic salts in the air to cause corrosion and condensation inside the wind turbine, as well as giving rise to bacterial growth and a risky working environment. Together, these result in a wide range of problems with mechanicals and electronics, as well as causing electrical glitches and expensive unscheduled downtime.

Filtration isn’t enough

Conventional filtration isn’t enough to remove corrosive salts from the air. In offshore operating environments, these salts are usually dissolved in moisture. This corrosive solution tends either to be sticky and clog up the filter, or pass right through in liquid form. The renowned low efficiency of such filtration systems means moisture laden with corrosive salts is spread throughout the insides of the nacelle and tower.

The hotter and more humid the wind turbine site, the bigger the problems with corrosion and filtration. As a rule of thumb, the rate of corrosion doubles with every 10°C temperature increase (at the same level of humidity). This makes any solutions just relying on filtering the air very risky in wind turbine installations in hot, humid climates.

Corrosion prevention increases manufacturing costs

To counter all this and to be able to ensure their customers the necessary reliability metrics, manufacturers of offshore wind turbines have to use materials, components and coatings featuring higher corrosion ratings and IP classifications — which are always more expensive.

And higher manufacturing costs don’t make it any easier to win contracts and customers.

Preventive advantage

The only really effective way to prevent humidity and corrosive salts getting inside the nacelles and towers of offshore wind turbines is by maintaining positive pressure inside them.

The patented Cotes Overpressure System is a combined dehumidifier/desalter that creates a dry, salt-free environment inside nacelles and towers by maintaining such positive pressure, helping keep moist, salt-laden air from ever getting in. The system is equally effective almost everywhere in the world.

The Cotes Overpressure System tackles the many problems caused by airborne, salt-laden moisture inside offshore wind turbines, by keeping both the humidity and salt content of the air under full control.

Lower production costs

Effective, reliable control of corrosion means wind turbine manufacturers can work with lower ISO 9223 classification requirements and lower IP classes — which means lower costs for wind turbine materials, coatings and components. The Cotes Overpressure System enables you to roll back key costings by as much as 10–30% because standard-spec coatings, parts and fittings are sufficient.

Protection during transport and storage

Cotes dehumidifiers also help keep nacelles and towers — and the expensive fixtures inside them — in ready-for-service condition while in storage and en route to the erection site. This provides big savings on commissioning as well as rolling back maintenance and service costs — and keeps up the in-service revenue stream.

Safer working conditions

Positive pressure is also the ideal way to maintain a forced air change in offshore wind turbines, in order to get rid of gases (hydrogen sulphides, ozone, hydrogen, etc.) from below the ground and/or given off by machinery and battery packs.

Helps with cooling, too

Attached to heat exchangers or cooling coils, the Cotes Overpressure System can also be included to boost the effectiveness of the cooling set-up inside wind turbines.


  • Moist, salt-laden air prevented from entering nacelles and towers
  • Lower manufacturing costs
  • Minimal corrosion and greater revenue-earning uptime
  • Better statistics for operating reliability
  • Better statistics for maintenance and service costs

 How Cotes solutions stand out

  • Patented solution that prevents problems from arising, rather than just trying to deal with the consequences
  • Humidity management, salt removal and cooling all available from one compact, lightweight unit
  • Work effectively in operating conditions almost everywhere in the world
  • Help ensure safer working environment
  • Tested and documented as significantly more effective than traditional salt filtration solutions


Related industries

For more about tackling humidity in offshore wind turbines,
please contact Mikael Zacho Jensen +45 5167 2903 [email protected]