Enhancing pitch control reliability with ultracapacitors

Clean energy, like most industries across the globe, has faced an enormous test in resilience over the past few months. With the onset of the pandemic and the devastating effects it has had on the renewable energy industry^[1], we’ve learned that risk can catapult to new and unexpected levels. 

Risk will always exist in business. It’s important that our industry continually discovers and implements technologies that enable business resilience. A technology that can help achieve higher reliability for wind farms is ultracapacitor energy storage for pitch control. Over the past two decades, hundreds of onshore and offshore wind turbines have deployed ultracapacitor technology for reliable pitch control in lieu of traditional battery technologies. At a time when our industry faces hardship on many fronts, it would be good for operators to consider the technical and business advantages of retrofitting turbines with ultracapacitor-based pitch backup systems to improve turbine performance, reduce downtime and increase revenue generation. 

The market shift toward ultracapacitor-based pitch control
Ultracapacitors—the fast-responding, power-packed energy storage devices that have been adopted into a variety of applications and industries—are the foremost pitch technology used for turbines today, taking the leading share position of 43% in newly installed turbines worldwide in 2015. Batteries take 20% of electric pitch systems; the remaining 37% of turbines are hydraulic. 

This is a significant shift in the industry considering that the first large-scale wind turbines operated with hydraulic pitch systems, and in the early 1990s, battery-based electric pitch systems were introduced. By 1999 the first ultracapacitor-based pitch backup systems came into play, igniting a strong trend toward their adoption. 

The technology is known for its special ability to provide a high surge of power—unlike batteries, ultracapacitors can capture and release energy quickly and efficiently. An ultracapacitor stores energy in an electric field, rather than in a chemical reaction, so it survives hundreds of thousands more charge and discharge cycles than a battery. Ultracapacitors operate in much lower and higher temperatures since they don’t contain chemicals that are susceptible to environmental conditions. These traits have made them desirable, especially for difficult-to-access offshore turbines and for turbines operating in exceedingly hot climates. 

Retrofit for reliability
Ultracapacitors are a critical reliability component of the turbine pitch control system, managing the pitch for each blade individually and performing critical functions by “feathering” the blades to enhance the efficiency of wind energy conversion, as well as shutting down the system by pitching the blades to zero in the case of high winds or a grid failure for fail-safe operation. Wind farms have the option to retrofit turbines with ultracapacitor-based pitch systems by removing existing batteries and installing a drop-in solution.

A pitch system retrofit offers the advantage of eliminating the two most common problems with battery-based pitch systems: consistent battery voltage faults and premature battery system failures.

Battery voltage faults often appear when a turbine reboots after a utility grid power failure, when there is a battery charger failure, or when the battery doesn’t charge in cold weather conditions. If the fault cannot be resolved remotely, a technician must climb the turbine to assess the problem. This results in additional maintenance and revenue loss for every hour the turbine remains out of operation. 

Premature battery system failures are also common, mostly when the battery system operates in extreme cold temperature conditions. High heat also affects battery performance and can contribute to battery degradation over time. Varying ambient environmental conditions makes it more difficult to predict battery system operational lifetime. Replacing battery systems, which is necessary on-average every four to five years and often within one to two years, is a costly process that requires more maintenance, frequent downtime to replace batteries or check on battery faults, and an increased number of turbine climbs, which increases risk to maintenance staff.

Many wind farms have reaped the benefits of minimizing the above-mentioned efforts by replacing battery-based systems with ultracapacitors. Once installed, most ultracapacitor-based pitch backup systems on the market will operate reliably for a minimum of 10 years, significantly reducing the cost of backup components and warehousing efforts, turbine climbs, and disposal efforts. Those responsible for daily turbine operations can gain back valuable hours to focus on optimizing revenue.

Reliability is the key issue here. While batteries are reliable for a multitude of applications, they do not provide adequate reliability for the pitch control application, which presents a much higher risk in terms of system accessibility and personnel safety. Wind farm managers should take stock of their battery-system failure rates for a realistic view of component costs, technician hours and revenue loss associated with battery system upkeep. Many operators who have retrofitted turbines with ultracapacitor-based pitch systems often say they have had a burden lifted from the day-to-day operations due to the streamlined functionality of ultracapacitor technology.

The fast eat the slow

Renewables have been accelerating, as evidenced by the milestone achieved in 2019 when U.S. renewable energy consumption exceeded coal^[2] for the first time in over 130 years. Even though the pace of business has recently slowed due to the economic impacts of the pandemic, one thing will remain true: our world moves at a much speedier pace than ever before, and the fast companies eat the slower ones. 

To stay apace with the most advanced wind projects, operators must use the technologies at their disposal to maintain their competitive edge. As operators look for ways to improve efficiency and boost profits, they should consider upgrading turbines with ultracapacitor-based pitch backup systems, which eliminate many of the problems associated with batteries. Ultracapacitor-based pitch backup systems have earned a reputation of reliability, increased safety and reduced overall operational cost—advantages that wind farms should leverage as they enter recovery and continue to move toward a future where renewable energy takes the lead.