Improvements in composite turbine blades will power the wind energy industry.
Wind is an increasingly important source of renewable energy. In 2015, wind power installations generated about 435 gigawatts (GWs) of power worldwide, approximately seven percent of all global power, according to the Global Wind Energy Council (GWEC). By 2030, GWEC projects that wind power could supply 2,110 GW, or about 20 percent of global electricity demand.
At least some of that growth will depend upon the advances made in the next decade in the composition, design and construction of composite turbine blades. Navigant Research, which specializes in analyzing clean energy markets, says that stakeholders involved in the wind turbine industry are devoting a greater amount of research and development investment to wind blades than to any other component in wind turbines. Blades are key to energy production; the longer the turbine’s blades, the longer the swept area and the more power they generate.
Long 73.5-meter blades are producing the power for Deepwater Wind’s new Block Island Wind Farm off the coast of Rhode Island. The five-turbine, 30-megawatt wind farm, the first offshore wind energy installation in the U.S., began feeding electricity into the New England power grid last December.
LM Wind Power manufactured the blades for the Block Island Wind Farm in Denmark, then
shipped them to the U.S. for installation in June 2016. Photo Credit: Deepwater Wind
GE Renewable Energy supplied the turbines. LM Wind Power, subcontractor for the turbine blades, built them at its Denmark plant and then shipped them to Block Island for installation in June 2016.
The 73.5-meter blades were the longest in the world when LM Wind Power introduced them in 2012, according to Lene Mi Ran Kristiansen, senior manager, communications and sustainability, global communications. “With this blade, several innovative features were introduced to keep the weight down and ensure a smaller root diameter, but it was based on existing polyester technology.”
The company used different materials to create its record-breaking 88.4-meter blade last June. A new hybrid carbon fiber material combined properties from the less-expensive glass fiber with very light but expensive carbon fiber. “With all the blades, there’s a balance to strike between weight and length, cost and performance,” says Kristiansen.
The challenges when building these giant blades are very much related to having adequate manufacturing facilities, equipment and logistics solutions to get them from the plant to their destination. That destination is offshore for these big blades, and tools that can cost effectively enable storage on land, transport by boat and crane handling offshore are key.
For manufacturing, several processes, such as laying up the raw materials in the mold had to be adjusted and rethought. With the huge size of the mold the operators are no longer able to reach out and manually put material in place in the way they can in smaller molds. In addition, as the vertical surfaces get bigger, the glass tends to slide down. These were just some of the production details that evolve into problems as the mold size increases.
It took lots of preparation and continuous dialogue to generate ideas and develop solutions that were the key to overcoming these challenges, says Kristiansen.
Reducing Variation
Molded Fiber Glass Companies (MFG) has been manufacturing blades, spinners, nose cones and nacelles for wind turbines for more than 25 years. “The units have to get cheaper to install, cheaper to operate and therefore provide more margin for the bottom line customers, the operators and finally the users of electricity,” says Carl LaFrance, senior vice president, quality. That means producing longer blades.
“When you double the length of a blade, you quadruple the amount of composites in it, unless you start narrowing down the design margin,” he says. A tighter design requires less variability in processes and materials. To gain more control over those factors, MFG is constantly looking for better materials, finishing technologies, and measurement and inspection methods.
Molded Fiber Glass Companies (MFG) manufactures wind turbine blades at its plant in South Dakota. Carl LaFrance, senior vice president, quality, says that “variation is the enemy” when it comes to composite blade production. Photo Credit: MFG
“We are driving our vendors to change their processes to reduce variation. Variation is the enemy,” LaFrance says. MFG wants to know, for example, exactly how much glass is in a particular volume of laminate. “If you put in more glass than you need, you’re paying too much money. If you put in less than you need, you risk failure.”
It’s essential to ensure that the glass goes in at exactly the right orientation or combination of orientations. “Blades are primarily unidirectional, because you want to tailor the strengths and stiffness in a very specific direction from root to tip,” says LaFrance. “If you are off by a degree in how you lay that material down, it can affect performance.”
MFG has developed some proprietary processes to help improve accuracy and is beginning to use robots for the production of smaller turbine components. (Blades are too large.) “We’re also doing some work using pultruded components for wind turbine blades, but there are technical issues associated with it that have not been resolved,” says LaFrance.
“The challenges in technology are really in the blades because they have to get bigger – much faster than cells or spinners do – and they have to get lighter and less costly. We are providing aerospace quality for a commodity price,” he says.
MFG’s customers design most of their blades with E-glass fiberglass, but some request S-glass if they require more stiffness or strength. Although some turbine blade designers are now incorporating carbon fiber into their blades to improve stiffness, using the material causes additional challenges. “It has a much narrower window for manufacture, and it doesn’t like bending at all,” LaFrance adds. Carbon fiber is also conductive, making it more susceptible to lightning strikes, which are the most common source of blade damage.
Developing Design Tools
GE’s Global Research Lab’s research with composite blades in the aviation industry has informed its work in wind turbines. “We have developed manufacturing processes – an understanding of materials and materials’ behavior and design tools,” says Shridhar Nath, technology leader, composites.
Molded Fiber Glass Companies (MFG) now uses a Combi-Lift blade handling unit, which has reduced its blade handling time and cost by an average of 70 percent. The company uses the unit to transfer blades to trucks for transport to the field sites. Photo Credit: MFG
He notes that longer blades present logistical as well as materials challenges. As blade size increases, transportation costs become a larger factor. GE is investigating whether a two-piece blade would resolve some of those issues, but that would require blade manufacturers to find ways to join them in the field.
The manufacturing process for such blades would be slightly different. “For example, where do you break the blade up? It places more emphasis on the design aspect; we have to understand what are the loads, what is the wind regime, what are the mechanical issues or the structural issues that go into those?” says Nath. “Those are the challenges that we are addressing and that we are working toward resolving.”
