Cold climate operation executive summary:
Wind turbines (WTGs) are an effective and sustainable source of renewable energy. However, operating wind turbines in cold weather conditions presents unique challenges.
The formation of ice on blades, gearboxes, generators, and other equipment can lead to reduced efficiency, increased maintenance requirements, and potential equipment damage.
Any ice that has gathered on the turbine and its parts can potentially dislodge due to temperature increase, wind, movement of the turbine and other external factors such as vibrations or gravity. This can lead to it being flung several hundred metres (ice throw) causing potential risk of damage to other wind turbines, structures, vehicles, or injury to site personnel and the public.
This technical summary outlines the issues encountered in operating WTGs in cold weather conditions and reviews some of the solutions adopted and risk mitigation strategies employed.
Principal considerations:
Ice formation:
Cold weather conditions, especially in regions with high humidity and low temperatures, can lead to the formation of ice on wind turbine components.
Ice accumulation on blades disrupts their aerodynamic profile, leading to reduced power output and increased load on the turbine structure. The altered aerodynamics can reduce power generation by up to 80% during an icing event. WTGs may shut down automatically to prevent damage, causing further downtime.
Ice can also affect the gearbox, generator, and other equipment, leading to operational issues and potential failures.
Any ice that has gathered on the turbine and its parts can potentially dislodge due to temperature increase, wind, movement of the turbine and other external factors such as vibrations or gravity. This can lead to it being flung several hundred metres (ice throw –design calculations consider a safe distance to be 2x tower height + rotor diameter) causing potential risk of damage or injury to other wind turbines, structures, vehicles, site personnel, and the public.
Mechanically speaking, if the wind remains constant and the turbine is in operation then all should be well. When turbines stop/idle and are not generating, this is when issues can arise.
Example from the field: Gear oil level alarms gave false readings as the oil was clinging to the gears and was lifted out of the sump. Oil pumps can trip due to oil viscosity. Note, UK based turbines generally do not have gear oil heaters.
Effects on wind turbine components:
- Blades: Ice accumulation on blades causes an imbalance, leading to vibrations and increased stress on the structure. This can result in reduced generation, increase wear and potential blade damage. When moisture in blades (or in damages on blades) freezes, it can cause those damages/imperfections to accelerate, some may require emergency winter repairs.
- Gearboxes: Cold temperatures and ice formation increase the viscosity of lubricants in gearboxes, leading to additional mechanical stress. This can result in reduced gearbox efficiency, increased wear and even gearbox failure.
- Generators: Ice accumulation on generator components can cause electrical insulation degradation, leading to increased electrical resistance, reduced generator output, and potential breakdowns.
- Bearings: Uneven ice accumulation causes rotor imbalance and increased vibrations, which puts additional mechanical strain on bearings. This increased fatigue loading can reduce the lifespan of the equipment and increase maintenance costs.
- Condensation: any asset that is prone to condensation can be unduly affected by freezing temperatures. Expansion as ice forms can cause issues on weaker structures or components, while ice melting concentrates the moisture and can saturate areas or components.
- Met-mast and measurement errors: Turbine performance can also drop due to ice on the met-mast, anemometer, or wind vane leading to inaccurate data and improper operation or control errors. Some met-masts have heating or instruments that are not affected by ice buildup unless substantial.
- Electrical system: Most cabinets will have heaters in them, so if sites experience outages, issues can be magnified.
Example from the field – A UK based WF had switchgear heaters, but the outage meant they did not have power. Returning assets to service after being off will take longer and more than likely require more parts/repairs.
- Battery backup: Back up batteries in the hub which are used to pitch the blades in a trip or outage can be affected by the cold. If these issues become severe enough, the turbine would have to be stopped until replacements can be fitted. If these batteries cannot pitch off, then it can lead to an overspeed (if wind speeds are high enough).
- Material brittleness: Standard materials like metals, plastics, and rubber seals can become brittle and prone to failure at very low temperatures (e.g., below -21°C) for some standard models.
- Lubrication issues: Oils and lubricants can become highly viscous ("stiff") in the cold, impeding proper flow and lubrication of the gearbox and bearings during start-up and operation. This can lead to increased friction losses and potential damage if components are not pre-heated.
- Component failure: Auxiliary systems such as pumps, cooling circuits, filters, and seals can fail or leak if not designed for cold-climate operations.
- Other equipment: Cold weather conditions can affect various other components, such as hydraulic systems, control systems, and tower structures, potentially impacting their performance and reliability.
- Accessibility: Heavy snowfall can make wind farms inaccessible for standard service vehicles, leading to longer downtimes between repairs.
Solutions adopted:
To overcome the challenges posed by cold weather conditions, several solutions have been adopted in wind turbine design and operation:
- Blade de-icing systems: Active and passive blade de-icing systems are employed to remove or prevent ice formation on blades. Active systems use heating elements or anti-icing coatings, while passive systems utilise blade aerodynamics and surface materials to minimise ice accumulation.
- Cold climate lubricants: Special lubricants with lower viscosity at cold temperatures are used in gearboxes and other rotating equipment to ensure smooth operation and reduce mechanical stress.
- Generator insulation: Improved insulation materials and designs are employed to enhance the resilience of generators against ice-induced electrical insulation degradation.
- Cold-weather tower design: WTG towers are designed to withstand extreme cold temperatures and associated thermal expansion and contraction. Adequate insulation and heating systems are implemented to prevent ice formation and enhance structural integrity.
- Remote monitoring and maintenance: Advanced remote monitoring systems are used to detect ice formation, monitor equipment performance, and schedule maintenance activities proactively.
Offshore note:
For larger offshore WTGs, OEMs have introduced additional safeguards for extreme winter conditions, (standstill preservation and winterization) as part of their long-term SWA (Service Warranty Agreement). Blade designs and foundations are now incorporating anti-ice coatings to prevent build up. Even with the foregoing safeguards, there are still significant risks to WTGs associated with being at standstill; offline for a significant period for maintenance; complete loss of power to controller; pitch/yaw systems; cabinet heaters; and dehumidifiers.
In-field experience: Start-up issues in winter, even at shorter periods of standstill with active idling and external power supplies. With significant temperature drops Operators can have start up issues with controllers, generally it is instrumentation on lubrication and cooling systems which do not have any form of trace heating on pipework/impulse lines, only heaters in switchgear and smaller electrical cabinets.
Risk mitigation strategies:
The following strategies are commonly employed:
Regular Inspection & Maintenance: WTGs operating in cold weather conditions require more frequent inspection and maintenance to identify/address issues promptly.
- Winterisation procedures: Before the onset of winter, WTGs undergo specific winterisation procedures to ensure readiness for extreme cold temperatures.
- Emergency shutdown systems: WTGs are equipped with automated emergency shutdown systems that activate in response to severe ice accumulation or other adverse weather conditions. This reduces the risk of equipment damage and ensures operator safety.
- Operator training: Proper training and expertise for wind turbine operators and maintenance personnel are essential to effectively handle cold weather challenges and carry out necessary procedures safely.
- Condition monitoring systems: Real-time condition monitoring systems are used to detect abnormal vibrations, temperature variations, and other signs of equipment distress, allowing for timely intervention.
Our team of experts believe that climate change, not limited to just winter, will require better management by OEMs and Operators.
Additional information:
Anti-icing systems:
Active de-icing: Heating elements embedded in the leading edge of the blades are used to prevent ice formation or melt existing ice. These heating elements are typically activated when temperature and humidity conditions indicate the possibility of ice formation.
Passive de-icing: Passive de-icing systems rely on blade aerodynamics and materials to minimise ice accumulation. These systems include special coatings that reduce ice adhesion, blade shapes that promote ice shedding, and materials with anti-icing properties.
Remote monitoring and maintenance:
Ice detection systems: Advanced ice detection systems, such as sensors or cameras, are deployed on wind turbines to detect the presence and extent of ice formation. This allows operators to take proactive measures to prevent ice-related issues.
Condition monitoring: Real-time condition monitoring systems continuously monitor various parameters, including vibrations, temperature, and oil analysis, to identify early signs of equipment distress caused by cold weather conditions.
Predictive maintenance: Data collected from remote monitoring systems and condition monitoring enable predictive maintenance practices. By analysing trends and patterns, maintenance activities can be scheduled proactively, reducing downtime, and preventing potential failures.
Cold climate lubricants:
Low-temperature gear oils: Gearboxes are filled with lubricants specifically designed for cold weather conditions. These oils have lower viscosity at low temperatures, ensuring smooth operation and reducing mechanical stress on gears and bearings.
Hydraulic fluids: Hydraulic systems in wind turbines use hydraulic fluids with low- temperature capabilities to maintain proper operation of pitch control systems, rotor brakes, and other hydraulic components.
Generator insulation:
Improved insulation materials: Special insulation materials with enhanced resistance to low temperatures and ice-induced electrical degradation are used in WTGs.
Insulation heating: Some wind turbines employ insulation heating systems to prevent ice formation on the generator and maintain proper insulation performance in extremely cold conditions.
Cold-weather tower design:
Thermal insulation: WTG towers are equipped with thermal insulation to minimise heat loss and prevent ice formation. Insulation materials with low thermal conductivity are used to maintain a stable internal temperature.
Tower heating: Heating systems are installed in WTG towers to prevent ice formation and ensure structural integrity. These systems use heating elements or hot air circulation to keep critical components free from ice.
From the field - e.g., Japan:
Construction and operation of wind farms in the coldest parts of Japan present unique challenges due to the extreme cold weather conditions. Below are some key considerations for wind farms in this region, but are applicable in regions that experience similar conditions:
Extreme cold temperatures:
Temperature considerations: The coldest parts of Japan experience extremely low temperatures, often dropping well below freezing point. This necessitates the selection of materials, components, and equipment that can withstand such frigid conditions.
Thermal expansion and contraction: Cold temperatures lead to thermal expansion and contraction of materials, which can affect the structural integrity of wind turbine components and foundations. Careful design and engineering considerations are required to account for these temperature-related effects.
Snow and ice accumulation:
Increased snowfall: Regions with cold climates in Japan experience heavy snowfall, which can lead to significant snow accumulation on wind turbine blades, towers, and other components. Snow build-up can reduce power production and cause imbalances in the rotor system.
Ice formation: Sub-zero temperatures also result in ice formation on wind turbine components, including blades, which can adversely affect their aerodynamic performance and increase structural stress.
Cold climate site preparation:
Foundation design: Special attention must be given to foundation design and construction to ensure stability and prevent frost heave caused by freezing and thawing of the ground. Deep foundation systems or insulation techniques may be employed to mitigate these effects.
Access roads and infrastructure: Proper planning and construction of access roads and infrastructure are essential to provide reliable transportation and operational access to wind farm sites, particularly during heavy snowfall and icy conditions.
Wind turbine design and adaptation:
Cold climate certification: Wind turbines installed in cold regions of Japan must adhere to specific design standards and certifications that take into account the challenges posed by extreme cold temperatures, snow, and ice.
Anti-icing systems: Wind turbine blades may be equipped with advanced anti-icing systems to prevent or reduce ice formation. These systems often include heating elements or passive measures such as coatings designed to inhibit ice adhesion.
Rotor blade design: Wind turbine rotor blades used in cold regions may be designed with special aerodynamic features to enhance ice shedding and minimise the impact of ice accumulation on performance.
Ongoing maintenance and operations:
Snow and ice removal: Regular snow and ice removal from wind turbine components, particularly blades and nacelles, is necessary to maintain optimal performance. De-icing techniques such as mechanical removal, heated brushes, or hot air blowers may be employed.
Remote monitoring and surveillance: Advanced remote monitoring systems, including cameras and sensors, can be used to monitor ice and snow accumulation, as well as detect any
potential issues related to cold weather conditions. This enables timely intervention and preventive maintenance.
Cold weather maintenance protocols: Maintenance activities should be adapted to cold weather conditions, considering factors such as temperature limitations for lubricants, winterised equipment, and cold-weather-specific inspection routines.
Summary
In summary, the construction and operation of wind farms in the coldest parts of Japan require specialised design considerations, materials, and maintenance practices to withstand extreme cold temperatures, snowfall, and ice formation. By addressing these challenges, wind farm operators can enhance the reliable and efficient generation of renewable energy in these regions
For more information, visit our power and renewable energy page or contact Joe Mead, Abid Sayeed, Martin Dobson or Alan Tucker.
