Palm Fronds: A Year of Wind Energy Innovation


Published Dec 26, 2015 5:14 PM by Wendy Laursen

In the most recent of this year’s innovations in wind farm turbine engineering, Professor Eric Loth of the University of Virginia has started building a small-scale prototype of a wind turbine, modelled on palm fronds, with blades that face downwind.

The blades spread out to catch the wind during good weather, and fold together like palm fronds in dangerous weather. The design is called a Segmented Ultralight Morphing Rotor – segmented so that the blades can be assembled on site from segments, and ultralight because the blades’ adaptability to the wind flow allows them to have less structural mass.

Loth and his team’s design would dwarf the largest and most advanced wind turbines in existence or in testing today. The largest of the team’s design would each produce 50 megawatts of peak power using rotor blades as long as two football fields. While such long blades may be impossibly heavy with conventional configurations, this new design concept may allow extreme-scale rotor blades to be much more lightweight.

Another issue is weather resilience. Although scientists and energy companies long to deploy turbines up and down America’s coastlines, where offshore winds could be turned into staggering amounts of power, no one wants to spend millions of dollars on turbines only to have them wrecked in an ocean storm.

“Palm trees achieve their resilience by a lightweight, segmented trunk structure that can bend in the wind,” Loth said. “They go with the flow. Similarly, our turbine design can morph downwind in very high winds and then stow away altogether in a hurricane, unlike conventional wind turbines.

“We hope our innovative concept will allow us to break through the technology barrier and allow the United States to be the world leader in wind energy.”

Two Blades

Earlier this year another innovation was announced with the construction of two-bladed designs where the rotor spins 180 degrees to face downwind.

2-B Energy, a Netherlands-based company, is set to build a prototype two-bladed offshore wind turbine with a 6 megawatt capacity off Eemshaven. The turbine is expected to power about 5,000 households by 2030.

While the potential benefits of two-bladed turbines are numerous, there are engineering issues to consider.

The benefits of two-bladed turbines include cheaper construction because they require fewer less material to construct and are easier to install. Industry leaders estimate that two-bladed turbines could cost about 20 percent less to construct and install while still generating the same amount of power as three-bladed turbines.

Removing the third blade makes the rotor lighter and allows engineers to place the rotor on the downside of the tower. In addition, two-bladed rotors are often easier to install than three-bladed turbines which must be constructed on-site. Because they often weigh up to 40 tons less than conventional rotors, two-bladed rotors can be built onshore and transported to its designated location on a ship because it is light enough to be lifted onto the tower.   

But there are still some engineering issues that must be addressed before two-bladed turbines become commonplace. Because the blades are lighter and more flexible, it is possible that the blades will spring back and hit the turbine tower in strong wind conditions.

Two-bladed turbines also suffer from dynamic imbalances. For instance, when the top blade is in the wind the bottom blade is being shaded by the tower. This causes problems with yawing and puts unnecessary wear on the bearings. This makes them particularly unsuitable for high wind areas.

No Turbines

2015 also saw an announcement from Vortex Bladeless, a Spanish start-up, which proposed a new way of harnessing energy from wind that doesn’t require turbines.

The new system generates electricity using the swaying of masts, which move magnets placed in a joint near the masts’ base. Vortices of air are formed along the structure, and this energy is used to generate electricity.

The company claims that this means the costs of a Vortex system is much lower than traditional wind turbines - about half the construction cost and about 20 percent of the maintenance costs. 

The lack of blades also means the system is quieter than traditional systems and less likely to kill birds.

The company has two models in development, a +1MW model for utilities and a domestic 4kW model. 

Kite Power

Also this year, Kite Power Solutions announced an electricity generation system that it believes is more economical than traditional offshore wind farms.

The company has embarked on a £10 million ($15 million) funding round to support the commercial development of its kite power technology and is aiming to deploy its first 3MW power system in offshore waters by 2019.

Bill Hampton, Founder and Chief Executive of Kite Power Solutions (KPS) says: “We will be able to compete with offshore wind, without subsidies, by removing tons of steel from every MWh produced offshore. Quite simply, by removing the steel from clean energy you make it lighter per MW and thus cheaper, and with a lower carbon footprint. Our kite technology is easier and cheaper to deploy and maintain.”

Hampton says the technology can cut the capex of offshore farms by as much as 50 percent. Offshore wind installations are currently priced at around £140/MWh ($217) and are projected to fall to £78/MWh by 2020.  KPS expects to reduce that cost to around £50/MWh by 2020.

The KPS power system has two kites that are flown on a man-made fiber tether between 500m (1,640 feet) to 750m (2,460 feet) in length. The tether is attached to a winch system that generates electricity as it spools out. By achieving flight speeds of up to 100mph in 20mph winds, tether tension causes the line to rapidly spool out from a drum which is connected to an electricity generator. 

KPS’s kite and cable system reduces the amount of steel required compared to a traditional system by over 75 percent, and the anchor system to hold the KPS installation is equipment routinely used in the offshore oil industry to install FPSOs and other large ships. The lightweight KPS system can therefore be deployed in far deeper waters. 

The depth limitations of the system will be economic, says Hampton, and driven more by distance from shore which drives maintenance costs and export power costs.