As countries such as the United States announce policies and goals focused on increasing renewable energy capacity, there are opportunities for new and improved renewable energy technologies. Xenecore, a New York City-based company developing more efficient wind turbine blades with higher energy capture capabilities, is using its expertise in composite parts to design and develop resistance-based fan-shaped wind blades.
Xenecore was founded in 2010 by Jerry Choe, CEO and founder of the company, through the use of material technology in sporting goods applications to develop carbon fiber composite tennis rackets, and formed a number of patents. In order to achieve a carbon fiber tennis racket with high performance and power while hitting the ball, and to minimize the impact of the racket on the arm, after an 18-month development period, he and his team developed a material and process solution, which is now marketed under the trade name Xenecore, a thermoplastic microsphere product that can be used as a structural core for composite parts.
Following these initial successes, the company invested heavily in the further optimization of thermoplastic microsphere technology and was awarded more than 250 patents worldwide. The company found that the use of Xenecore products could extend beyond tennis rackets to new opportunities for other applications, such as drone blades and, more recently, resistance-based wind turbine blades.
About two years ago, Choe and the Xenecore team began looking into how the company's process technology and products could be used to develop wind turbine blades. Today, most wind turbines have slender aircraft-shaped blades that generate electricity primarily from lift. As the wind passes through the blades, the lower pressure formed on one side of the blades pulls on the blades perpendicular to the wind direction, causing them to rotate the rotors, transferring energy to the turbine to generate electricity.
These blades are usually made of fiberglass skin, and in longer blades are supported by a carbon fiber composite wing SPAR cap. Wind blades are usually placed in an open mold, vacuum injected, and then assembled together using a shear web, foam core, and adhesive.
The earliest windmills, however, looked very different, featuring wide, flat, fan-shaped wooden blades that generated electricity through resistance, with the wind directly used to push the blades in the direction of the wind. When wind turbines were first invented, everyone was using drag because it captured more wind. But these first blades were a problem because of the materials used, as the earliest windmills were built with soft, less durable materials such as cloth.
In 1919, German physicist Albert Bates published his now-famous Bates Law on wind capture and blade design. According to this law, the blade can only capture a maximum of 59% of the wind energy using lift. This theory influenced the shape of aircraft wings and wind turbine blades to maximize lift and minimize drag, using thin, curved designs that are still popular today.
According to Choe, the 59 percent energy capture rate is a theoretical maximum because actual wind turbines capture energy much less efficiently, but it is not the maximum for today's materials. Because the fiberglass and carbon fiber composites used today are stronger and lighter, they perform much better than the metal materials used to make blades and wings in Bates's day. Therefore, given that existing material properties have been optimized, the best design may now be inefficient and no longer meet the requirements.
It is worth noting that there are a number of resistance-based wind blade designs that have been in use for a long time, such as the Savonius type vertical wind turbine, which features two cup-shaped blades that rotate around a central turbine. These turbines are generally much less efficient than lift-based turbines because, in a vertical setup, the two blades actually block some of the wind that the other half of the blade can capture. However, their simple design and ability to capture energy in low wind areas make them popular for turbines in home or commercial environments.
Choe and his team set out to develop a newer horizontal wind turbine that maximizes drag and, most importantly, uses advanced composite materials.
One of the early challenges the Xenecore team faced was that since lift-based turbines have become the standard, today's simulation software is only used to analyze the performance of lift-based turbines. Choe and his team tried a number of analytical tools and eventually used Ansys Fluent computational fluid dynamics software to model the behavior of the wind on the blade.
Using these models, the goal is to develop a blade that can capture maximum drag, generate electricity inside the turbine, and at the same time withstand high wind loads with as little weight as possible. The Xenecore team first tried to make a solid carbon fiber composite blade, but the strength was not good, even solid carbon fiber plates can break under high winds.
Finally, Xenecore designed a single fan-shaped blade, called a Fanturbine, consisting of a top and bottom skin covered with Xenecore thermoplastic microspheres. These skins are reinforced with ribs called I-beams. The design is bionic because the ribs fan out from a central point, much like the leaves on a palm leaf.
The blades are manufactured in a one-step compression molding process using high-modulus carbon fiber and epoxy resins to maximize strength and stability, and to resist high wind loads with the lightest possible weight. The one-piece monomer design is also designed to maximize stability and theoretically extend the life of the blade, as there are no joints or adhesives that can damage or fatigue over time. Currently, the first version of these blades is relatively small, measuring 3 by 3 feet, with the goal of scaling up to a larger size to compete with conventional wind blades.
To produce each blade, the cut carbon fiber fabric is placed in an aluminum top and bottom mold, and multiple layers of Xenecore film paper are placed on top of each skin. The mold closes, and under high temperature and pressure, the microspheres expand into a lightweight structural foam that binds to the cortex. The process produces a single, seamless, binder-free, free-moving single part of the I-beam.
Xenecore's turbine design consists of four fan blades on each turbine, covering approximately 80% of the available surface area. The wind pushes the blades and spins the rotors, which creates energy in the turbine. According to a 2021 white paper by the late Dr. Paulo Abdala, professor of aviation at the University of Brasilia, the amount of electricity generated is largely dependent on wind speed. The robustness of the flat fan-shaped blades helps create steep pressure differences on the sides of the blades, which increases wind speed and power generation.
According to Xenecore's simulations, under ideal conditions, the fan could theoretically achieve a maximum of 98 percent wind energy capture. In addition, the blade is designed to withstand hurricane-force winds, and in simulations, it proved to withstand winds of up to 376 miles per hour, well above the top speed of a hurricane. According to Choe, these blades can operate on existing turbines without changing existing infrastructure.
In 2022, Xenecore began production of 5 kW small turbines with 3 x 3 foot blades and sold them to distributors in South America and online worldwide. These small systems are designed to replace similar power solar panels used in homes and businesses, providing the same amount of power, but they perform much better and cost three times less to run, Choe explained.
The blades have been tested to produce seven times more power than conventional wind turbines of similar size. The largest system Xenecore has tested is a 100-kilowatt turbine with blades 11 feet wide. It has a megawatt-level version in the works.
Choe said there is a lot of interest in larger Fanturbine blades in the near future, noting that the technology has the potential to retrofit French GE's Haliade X turbine, currently the largest, which could increase its capacity 100-fold, from 14 megawatts to 1.4 gigawatts.
Currently, the company is looking for investors and partners to help take the technology to the next stage. To prove the technology, Xenecore's next step is to build and install a 1 MW turbine on a retrofit decommissioned wind turbine tower.
