The Advantages of Ultracapacitors in Wind Turbine Electric Pitch Control Systems
June 22, 2015 | Stefan Werkstetter, Sr. Field Applications Engineer
There are two types of energy storage systems used for electric wind turbine pitch control: ultracapacitor-based and battery-based. While batteries are efficient devices for many applications, ultracapacitors have the advantage when it comes to supporting a wind turbine’s electric pitch control system.
Pitch control systems are used to help prevent mechanical stress to the wind turbine by continuously adjusting the blade pitch in line with the operation strategy of the wind turbine. This not only ensures constant power output of the wind turbine, but also reduces mechanical stress to the turbine structure, extending its service life.
As we all know, power supply can fail. If the energy grid happens to fail, the turbines need an emergency backup plan. That backup plan is an energy storage system that provides enough energy to return the turbine blades to a neutral position for safe shutdown, which prevents severe damage or total loss of the wind turbine due to strong and uneven wind forces. Ultracapacitors provide these top five advantages over batteries when used as the energy storage system for wind pitch control.
1. High power density = burst power
Unlike batteries, ultracapacitors provide the burst of energy that is needed to return the turbine blades to a neutral position in the event of a grid power failure. They charge faster than batteries and are highly reliable for short-term mismatches between power demand and power availability.
2. Lower total-cost-of-ownership
The upfront cost for an ultracapacitor-based electric pitch control system is the same as a battery-based system. However, the cost for the electrical system (excluding the energy storage device) is more costly for a battery-based pitch control system because batteries require more complex charging and monitoring systems. An ultracapacitor-based system requires fewer components and simpler mechanical mounting and vibration damping than batteries.
3. Long service life and predictable aging
On average, ultracapacitor life span is 12 years under normal operating conditions. This is largely credited to two main factors: the ultracapacitor’s ability to perform in a wide operating temperature range of –40°C to 65°C and an impressive typical cycle life of 500,000 to 1 million charge/discharge cycles.* It’s not uncommon for ultracapacitors to operate with an efficiency of 97% and higher. Unlike ultracapacitors, batteries have a narrow operating temperature range. Harsh environmental conditions and continuous cycling takes a heavy toll on batteries, and they often need replacement every two to four years.
4. No heating or cooling costs
As mentioned above, batteries are vulnerable to the extreme temperatures that ultracapacitors can endure. Batteries require heating and cooling systems, so it’s inevitable that your design cost for a battery-based system is going to be higher. Ultracapacitors eliminate the need for these extra, high-maintenance systems.
5. Light weight
Battery-based energy storage often has to be oversized to accommodate peak power demand—even if this demand occurs only for a few seconds. As a result, battery-based systems are bulkier and weigh more. Ultracapacitors are significantly lighter, and because they have no problem providing burst power during peak power demand, they don’t require oversizing efforts.
To put this all into perspective, let’s consider an offshore wind farm. It’s an arduous process to send a repair person out to an isolated offshore wind farm for battery maintenance. Considering the advantages of ultracapacitors, wind farm owners and operators can save a lot of time and money by designing in the ultracapacitor from day one.
In the long run, batteries will rack up maintenance and replacement costs that ultracapacitors can almost completely eliminate.
* Results may vary. See warranty details and datasheet for applicable operating and use requirements.
Senior Field Applications Engineer
About this author
Stefan Werkstetter works from Maxwell’s office in Munich, Germany as a senior field applications engineer. Stefan is a state-certified electrical engineer with a focus on computer science. He has several years of experience in electrical systems pre-development, evaluation and testing. Prior to joining Maxwell, Stefan worked in the automotive industry for a German original equipment manufacturer and as a technician in telecommunication electronics. On his free time, Stefan enjoys hiking, camping, gardening and spending time with his wife and two sons.
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