Wind power has the potential to lower energy costs, reduce reliance on fossil fuels and power all of civilization…so why not harness it to the fullest?
Driving along the highway, it’s hard to imagine giant wind turbines with their lackadaisically circling blades can generate enough energy to power much of anything. Turbines, it turns out, make a difference: About 4 percent of the world’s energy production comes from the wind.
That percentage is steadily rising, but wind harvesting is nowhere near what it could be. High-altitude wind innovations could change that.
The trick is capturing that high-altitude energy and bringing it down to earth. There are different ideas for accomplishing this, ranging from a high-tech kite to a helium-inflated turbine to an autonomous figure-eight flying plane.
Wind energy at the ground level tends to be unreliable in most places, but scientists have shown that higher upwinds can be stronger and more dependable. This translates into exponentially more energy: eight times as much potential power for every doubling of wind speed.
According to Cristina Archer of the University of Delaware and co-author of the first global survey of high-altitude wind energy, winds between 1,640 and 40,000 feet had more than four times as much energy as surface breezes—enough, the study estimated, to power all of civilization 100 times over.
“The resource is amazing, and the potential is tremendous,” Archer said.
Harnessing High Winds
California-based startup Makani Power, which Google purchased in 2013, plans to one-up Ben Franklin with a device they call an “energy kite” that could eventually produce power at rates competitive to coal and natural gas.
It looks like an insect-thin airplane with eight propellers on the leading edge of the wing. The kite is designed to fly in circles at 500 to 1,000 feet, anchored to a ground station by a flexible tether made of aluminum and carbon fiber. The spinning rotors turn brushless DC motors to generate electricity.
A computer system fine-tunes the flight path as the wind and weather conditions change.
The design simulates the tip of a wind turbine blade, which produces as much as 70 percent of the total energy. If the winds slow, the rotors can act like helicopter blades, providing extra thrust to keep the kite aloft. If the breeze dies completely, the kite can land safely by reversing the process.
The kite’s ground footprint is much smaller than a traditional turbine and uses about 10 percent of the materials. Operational testing of a 600 kilowatt energy kite could begin in late 2016 or early 2017.
That’s in part because airborne wind systems can operate in far more places than ground turbines, such as valleys. By Makani’s estimates, energy kites could potentially work in over two-thirds of the continental U.S.
Even if high-altitude wind systems can’t compete with standard electrical grid rates right out of the gate, they could still be a big help at isolated locations like military bases, disaster sites and islands, places that otherwise have to rely on generators and expensive imported fuel.
A Low-Cost Green Energy
Massachusetts-based Altaeros Energies has a high-flying device with the potential to reduce this reliance, especially in areas like Alaska, where electricity prices can be ten times the national average.
The Alaska Energy Authority awarded Altaeros a $1.3 million grant to test the world’s first commercial high-altitude wind turbine, with the goal toward providing power to remote rural communities.
Altaeros’s buoyant air turbine, or BAT, is a bulging cylinder inflated with helium. It features a rotating turbine inside and has four stubby fins around the outside. Three load-bearing conductive tethers attach it to a ground station.
In 2012, Altaeros successfully tested a prototype that generated twice as much power at 350 feet as it did at 100 feet. The company hopes to offer power at about 18 cents per kilowatt per hour, roughly half the going price in remote Alaska.
The BAT can be assembled quickly and be used to lift cellular or internet antennas, cameras and weather sensors. It’s designed to work in heavy downpours and winds of more than 100 mph. If the weather gets too severe, the automated control system reels in the BAT to dock at ground level and wait until things improve.
The Sky’s the Limit
To compete with conventional turbines, airborne wind power designs will have to be almost completely autonomous and reliable over long periods. Then there’s the risk of having a large device covered in spinning blades suspended high overhead by nothing more than the wind.
The PowerPlane by Dutch company Ampyx Power addresses this problem by using a complex array of sensors to take off and land on its own, even if its 0.8-inch tether breaks.
In between, the plane flies in a figure-eight pattern that lets it move faster than the wind, like a water skier slaloming behind a boat. The plane generates power by yanking on a winch attached to a generator on the ground.
At a predetermined tether length—the plane can fly up to 1,500 feet high—it switches to descent mode and the generator starts reeling in the tether for a certain distance. Then the plane starts climbing and pulling again.
A prototype model with a 40-foot wingspan can produce about 50 kilowatts, enough to power roughly thirty houses. The team plans to have two PowerPlanes flying by the end of 2016. As soon as 2018, they hope to have a 2MW commercial model available. With a 100- to 130-foot wingspan, it would still use only 8 percent of the material of a comparable ground turbine.
High-altitude systems don’t work everywhere, Archer points out, starting with no-fly-zones near airports, power plants and government buildings. A larger concern is how to regulate and insure them.
“Right now there isn’t an official category for airborne wind power devices,” she said. “No insurance company is going to insure them without one, and they’re still fighting over whether they are ‘unmanned vehicles,’ ‘obstacles to aviation’ or even something recreational.”
If the technology proves itself, though, the sky is truly the limit. The fastest winds of all, with the highest wind power density, await in the jet streams, five miles high.
Feature photo credit: Tony Webster, Creative Commons, 2.0, https://flic.kr/p/pskKMf.