By Sam Salem and Peter Nyegaard Jensen, Wind Cluster
The February 2021 freeze event in Texas attracted attention to wind turbine behavior in cold weather. Wind generation fell short of expected output but was not the main driver of the extensive power outages experienced across the state. Wind turbines have proved to generate power successfully in cold environments (many northern European countries get a significant portion of their electricity from wind power year-round) if the right preparations are made. And with many climate scientists expecting an increase in extreme weather events — including freezing temperatures — cold climate operation presents a niche market for wind turbine OEMs if they can keep blades spinning during winter.
The accumulation of ice on the surface of wind turbine blades may cause a harmful unbalance on the rotor, causing issues with production and structural design loads. Ice shedding from a blade can damage other blades, hit the roof of the nacelle or even cause hazardous situations for properties and passers-by.
A sensitive ice detection system will be the first step to provide an early warning. Looking at the weather, operational signals and using commercial ice detectors are a good starting point. There are many ways to detect ice formation: visual, mechanical, differential pressure, vibration, ultrasonic and optical. Modern ice detectors, like the ones by New Avionics Corp., are entirely optical. A tele-component light source and receiver monitor the opacity and refractive index of whatever substance is in contact with the detector probe. The optical ice detector works as a combined optical spectrometer and optical switch. A change in opacity registers as rime ice; a change in refractive index registers as clear ice. Modern ice sensors are generally lower in cost, lightweight and smaller in size. Relay contacts send a “go/no-go” or “ice/no-ice” signal to the host control system. They run on a DC power source of 8 to 30 V and need only 2 W of power to operate. Ice detection can be installed as a retrofit on the turbines in service.
In places like Texas, where wind-turbine icing is rare, stopping the turbine may be the cost-optimal solution. To minimize production loss due to icing, a combination of forecasting, detection and mitigation should be used. Better predictability also lets operators determine if and when to shut down wind farm operations altogether. There are instances when the sun can melt the ice. If models indicate severe icing probability, ice forming too thick or too fast, then stopping the wind turbines will be the action to take. In this case, forecasting plays a big role in mitigating outage risks.
In areas where icing may happen more often, it may be advisable to also consider ice-prevention measures. Ice prevention systems allow wind turbines to continue operating during winter months. There are a number of ice prevention systems that include passive systems such as ice-phobic or ice-resistant coatings, and active systems such as hot air or electro-thermal systems.
Ice detection and ice prevention technologies are improving, and their costs are going down. Energy production in the cold season with strong winds and high electricity prices is a big opportunity for wind turbines. But it requires better forecasting, early detection and risk mitigation.
Sam Salem is the regional manager of Wind Cluster for USA and Canada. Peter Nyegaard Jensen is the managing director of Wind Cluster ApS in Denmark.
This story uses information from previous original Windpower Engineering & Development and Wind Systems reporting, and Lasse Hietikko, Business Development Manager of Wicetec, was interviewed for source material.
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