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CASE STUDY: Blade Pitch Control Adds More Power per Tower

blade pitch controlA leading global wind turbine OEM had been in the business for over 40 years. Its wind turbine fleet numbered in the 600s worldwide. Those turbines had churned out more than 15 million run time hours.

To compete with the next generation of wind systems, the company needed to decrease the cost of the energy it produced -- but couldn’t. At least, not until its quest to build a more efficient wind turbine led it to pitch control.

With advanced blade pitch control technology, the OEM was able to use the same tower structure and upgrade from a 24.4 m rotor to a 33 m rotor, decreasing the cost of energy produced.

This case study quantifies the change in this customer’s product -- a change that was made possible by switching to a pitch-controlled turbine design.

The Problem: The Need for a More Efficient Wind Turbine

As the size of a turbine goes down, there’s a handful of fixed-cost items that don’t decrease at the same rate. So that’s where the margins and the precision of the design is important in helping minimize fixed costs.

The OEM was looking to improve on its wind turbine design with a new version. By building a tower that generates more electricity throughout a greater range of wind speeds, the company could decrease the buyer’s LCOE (levelized cost of energy). LCOE represents the lifetime costs of electricity divided by the lifetime power generated.

Wind energy math is complicated, but there’s one simple truth: Bigger is better. Installing a larger rotor would increase the turbine’s “swept area,” raising the structure’s exposure to the wind and therefore potential for energy production.

It’s no secret that wind energy giants like GE and Vestas are moving to larger turbines. Some are now even being produced in the 10 mW range. Generally speaking, the reason for this is that LCOE is improved with a single 10mW machine compared to five 2 mW machines. And the “bigger is better” advantages can translate to smaller machines in the distributed wind market, too.

But the OEM’s current stall-regulated design wouldn’t support a larger rotor -- yet.

Enter: the Windurance Blade Pitch Actuator. Adding pitch control allowed the customer to propel its products into the next generation of efficiency and cost of energy thanks to the larger, more capable rotor that could now be utilized and configured precisely for the wind conditions at hand.

The Solution: Pitch Control

The OEM was already aware most modern turbines have blade pitch actuators. What’s unique about its solution is that Windurance provided a new pitch control actuator that allowed adaptation of a much larger rotor for the new model.

In addition to allowing the blades to be precisely and individually pitched for wind speed, pitch control allowed the same tower structure from the OEM’s older model to be used on this larger machine. 

Pitch Controlled Vs. Stall Controlled Wind Turbine

At any given moment there many factors affecting turbine efficiency. That’s why a turbine needs a control system. So, what makes a pitch-controlled system different from the norm? 

The OEM’s earlier models are all stall-controlled. In stall-controlled turbines, the shape of the fixed blade causes drag to increase as windspeed increases. This results in a gradual, passive, aerodynamic braking mechanism but not without some challenges. Stall control is a very complex aerodynamic design, and creates challenges in structural dynamics when trying to keep the whole turbine from vibrating. Aerodynamic efficiency is also sacrificed. 

But with blade pitch control, you can get more power out of the rotor and tune the shape of the blades based off wind speed.

The difference between pitch- and stall-regulated wind turbines is most noticeable during high winds. While stall-regulated systems rely on aerodynamic blade design to control the rotational speed in high winds, pitch-regulated systems use an active control for the blades. In other words, a pitch system has a constant power output above the rated wind speed, while stall systems can’t create consistent power output in high winds.

The Results: 40-60% Boost in AEP

Characteristic

No Pitch Control

Windurance Pitch Control

Control Method

Passive Stall Control (Fixed Pitch)

Active (variable) pitch control

Rotor Diameter

24.4 m

33 m

Rated Power

95 kW

100 kW

Cut-In (Startup) Wind Speed

3 m/s

2 m/s

Rated Wind Speed (Wind speed at which rated power is reached)

12 m/s

9 m/s

Design Lifetime

20 years

25 years

 

The main effect of the increased rotor size and pitch system addition was dramatically increased AEP (annual energy production) -- 40-60%, depending on average wind speed! 

The setup improved the OEM’s economic advantage for sites with lower average wind speeds.

The larger rotor allows the new model to start up at a lower wind speed, and it hits rated power output much more quickly.

 

Average Wind Speed

No Pitch Control

Windurance Pitch Control

% Increase

4.5 (m/s)

152

250

64%

5 (m/s)

196

305

56%

5.5 (m/s)

240

357

49%

6 (m/s)

284

404

42%

6.5 (m/s)

325

448

38%

 

Below, power curves estimate annual energy production in the current and previous iterations of the turbine. Power performance is based on standard conditions as defined in IEC 61400-1, with air density of 1.225 kg/m. AEP estimates are based on Rayleigh wind speed distribution and 100% availability.

blade pitch control - power curve graph

 

Other Benefits of the Pitch Actuator

There are several other benefits of blade pitch control. Some of them are exclusive to Windurance products:

You can read more about these features here.

Precision Engineering

The pie-in-the-sky idea of more power per dollars spent is possible -- but only with the latest technology. The customer realized an off-the-shelf product would never optimize cost efficiency.

There are other blade pitch solutions out there, but you’ve got to piece them together yourself. Windurance offers specific, fit-for-purpose pitch actuators made with 100s of years in combined experience. Just like the customer in this case study, yours can be precision-engineered to meet the cost and design requirements of your turbine.

Windurance was able to create a custom wind turbine solution for this OEM, and we can adapt our solution to your needs, too. Get in touch with our engineering experts below:

Ask Windurance a Question

 

Author: Windurance