Usage of Supercapacitors in Wind Turbine Pitch Control Systems: Economic Analysis
VINATech, Co., Ltd.
1. General Overview
The main function of the pitch control system in a wind turbine is to adjust the angle of the blades depending on the direction of the wind to maximize power output. In case of severe storms, the pitch control system is responsible for shutting down the blades to prevent the system from damage and failure.
During recent decades, supercapacitors’ role in wind energy has been dramatically increasing. Many pitch control system manufacturers have been choosing supercapacitors for the electrical pitch control systems to challenge the traditional way. Why do many pitch control manufacturers have considered supercapacitors as the best alternative to battery-based systems?
Generally, pitch control systems are divided into hydraulic and electrical systems. Electrical pitch control systems use batteries or supercapacitors as the power backup source. We will refer to electrical pitch control systems which use batteries for a backup power source as “battery-based pitch control systems”. Similarly, electrical pitch control systems which use supercapacitors as a backup power source will be referred to as “supercapacitor-based pitch control systems”.
2. Cost Analysis
Using supercapacitors as a backup power source in electrical pitch control systems is associated with lower costs when compared to battery-based pitch control systems due to a longer life cycle, little or no maintenance, and no requirement for heating or cooling systems.
Contrary to battery-based systems, supercapacitor-based pitch control systems require little or no maintenance due to the wide operating temperature of supercapacitors. Supercapacitors can operate in extremely low and high-temperature environments, ranging from -40°C to +65°C. The usage of supercapacitors doesn’t require any heating and cooling systems, which results in lower costs.
When comparing the supercapacitor-based pitch control system to the battery-based ones, it’s important to notice the difference in the life cycles. Supercapacitors have longer life cycles than batteries since they go through thousands of short charge-discharge cycles.
Thus, supercapacitor-based pitch control systems have a life cycle of more than 10 years while battery-based systems are characterized by 2 to 4-year life cycles.
Due to the shorter life cycle, batteries need to be replaced every 2 to 4 years which leads to additional costs. This also leads to an increased shutdown time during which a turbine doesn’t operate. This shutdown state of a wind turbine is referred to as the “State of Absolute Unavailability”(1). The state of absolute unavailability is one of the biggest cost components associated with the maintenance of wind turbines. During this state, a wind turbine is not producing any electricity which results in wasted power.
In the case of battery-based systems, the maintenance time related to the battery replacement varies depending on different factors. In the case of a 2MW wind turbine, the average downtime caused by pitch control system failure (including battery-related ones) is approximately 4 hours(1).
The state of absolute unavailability of wind turbines caused by the battery replacement occurs at least every 4 years and is about 4 hours. Therefore, during a 20-year period (typical wind turbine life cycle) there are at least 4 times when the wind turbine is in a state of total unavailability caused by the replacement of the battery. Corresponding to this, during a 20-year period, the total shutdown time for one wind turbine would be about 16 hours. In the case of a wind park consisting of 21 2MW turbines, the total 20-year shutdown time would be equal to 336 hours.
In the case of the Vestas 2MW wind turbine, 601.10 kW/h are produced with a wind speed of 7 m/s(2). If we assume that the price of electricity is equal to 21.27 cents per KW/h (average electricity price in Europe in 2020(3)), then, based on the assumptions mentioned above, the following calculation of wind turbine unavailability cost can be proposed:
0.2127 × 4 × 601.1 = €511.4
In this example, every 4 hours of shutdown caused by the battery replacement can lead to the approximate cost of €511.4. If we consider the period of 20 years, the total cost would be equal to €2,045.6. Furthermore, in the case of a 21-wind turbine park, the total 20-year cost of unavailability caused by the battery replacement would be equal to €42,957.6.
However, in the example of a supercapacitor-based pitch control system, since the replacement occurs only once during a 20-year period, the associated cost for a 21-turbine wind park would be about 16 times smaller – €2,684,9 (0.2127×601.1×21= €2,684,9).
Figure1: Cost of Downtime Associated with Battery and Supercapacitor Replacement in Pitch Control Systems
As for the total cost of ownership, the supercapacitor-based pitch control is considered to be at least 2.5 times more cost-effective than a battery-based system when considering a 20-year life cycle of a wind turbine.
As we can conclude from Figure 2, due to the regular replacement of batteries in pitch control systems, the cost of ownership of battery-based systems is significantly higher than the cost of ownership of supercapacitor-based systems.
Figure 2: Total Cost of Ownership of Supercapacitor and Battery
3. Eco-friendliness and Safety
Supercapacitors are widely considered to be an eco-friendly energy solution due to the lack of chemical substances, absence of heavy metals, and the resulting easiness of utilization. Supercapacitors are made of pure carbon and the cases are usually made of aluminum. Contrary to supercapacitors, batteries are made of lithium, nickel, manganese, graphite, and other materials, which are not eco-friendly and bear a risk of explosion.
Since wind turbines are mostly located in remote or rural areas, the safety aspect is one of the most important reasons why the usage of supercapacitors in pitch control systems is becoming more and more popular.
The Annual Energy Production (AEP) of a wind turbine is the total amount of electrical energy produced over a year.
Supercapacitor-based pitch control systems help to increase AEP by minimizing shutdown time and maintenance cost. Moreover, supercapacitor-based systems offer a safer and eco-friendlier alternative to battery-based systems.
Wind turbine manufacturers, which in most cases provide the regular maintenance of wind turbines, are likely to increase the efficiency and cost-effectiveness of their maintenance operations by using supercapacitor-based pitch control systems.
4. Case of 2MW Wind Turbine Application: VINATech Pitch Control Supercapacitor Module
VINATech’s Pitch Control Supercapacitor Module can be customized for different types of pitch control systems.
In the example below, the VEM16R0606QG module was customized for a 2MW wind turbine.
• Rated Capacitance: 60F
• Rated Voltage: 16V
• Operating Temperature: -40°C ~ 65°C
• Cycle Life: 500,000 cycles
In this case, VINATech’s supercapacitor module VEM16R0606QG has been successfully used in 2MW wind turbine pitch control systems for more than 5 years. This proven track record demonstrates the reliability of VINATech’s supercapacitor modules as the main alternative to traditional battery-based systems.
VINATech’s Pitch Control Supercapacitor Module can be customized for different types of pitch control systems and wind turbines.
Please, feel free to send us your inquiries at: https://www.vinatech.com/eng/contact/inquiry.php
(1) Carvalho, M., Nunes, E., Telhada, J. (2013a). Maintenance costs of a pitch control device of a wind turbine. Proceedings of the World Congress on Engineering 2013, July 3-5, London, 569-574;
(2) Wind Turbin Models: Vestas V 90;
(3) Electricity Price Statistics - European Commission.