Wind power in its traditional form of wind turbines sitting atop towers has become a mature industry and the improvements to the technology these days largely comes down to designing and building a larger or more efficient wind turbine. But the search for high intensity and consistent winds has been the holy grail in the wind energy industry in recent times and while the high altitude winds are up there waiting to be tapped, coming up with the technology to make it possible still eludes us.
The latest news story surrounds Google’s acquisition of Makani Wind Power, the high altitude wind technology manufacturer. Makani has developed the Airborne Wind Turbine (AWT) which is a high altitude wind power-generating device that looks like a wing and has multiple turbines attached to it.
These AWTs are essentially unmanned ultralight planes that are tethered to a tall base where they will float like a kite at heights between 250 and 600 metres. At this height the wind is stronger and more consistent compared to the usual wind turbine height.
The whole high altitude wind energy sector is still very much on the speculative side of the wind power production industry. There are a number of innovations that have been created and are largely still unproven. Although many of the new high altitude wind devices may generate electricity, the question remains whether the devices are going to be commercially viable in their construction and ongoing maintenance.
Those who support the concept of high altitude wind power argue that the cost of producing this form of energy could eventually become easier and cheaper to deploy. The towers that are required for the traditional wind turbines will no longer be necessary and the technology that goes into ensuring the turbines are facing into the prevailing winds will also be removed.
Reasons Why High-Altitude Wind Power Generation Is Sought
- Construction requires far less material
- Devices are smaller and lighter with less impact on the environment
- Wind speeds are higher and more consistent the further up into the atmosphere you go.
- There are fewer environment issues to deal with as you move higher into the sky.
- The NIMBY protests reduce greatly because the wind generation source will be out of sight and out of mind.
- The potential available space is almost unlimited.
Reasons Why High Altitude Wind Power Generation Is A Long Way Off
- The logistics of safely suspending turbines in the air are enormous and costly.
- Bringing any high altitude wind project to scale is going to be difficult considering today’s technology.
- The cost of maintenance would be prohibitive.
- The cost of hooking the generated power into an electricity system is high.
- Possible aviation hazard
Listed below are 7 high altitude wind power devices that have been developed and are currently being tested or are still in the early planning stages.
Makani Wind Power Airborne Wind Turbine
Makani Wind Power appears to be one of the closest companies to bringing the concept to a point where it might be deployed. The technology that is used to generate power involves a carbon fiber wing measuring almost 100 feet across that carries wind turbines. One of these wings would have the capacity to generate 600kW of power. The energy that is generated from the device could be transferred to the electrical grid through the tether line that holds the AWT in place. This tether might be attached to a ground-based substation or buoys out at sea.
In 2010 Makani was awarded a grant from the Advanced Research Projects Agency for the Department of Energy (ARPA-E) as a response to a call for proposals for what were known as “disruptive technologies”. Current testing has reached the stage where a model that is 30 feet in length is being trialed and is capable of generating 30kW of power.
The image to the right depicts the AWT on the runway before a test flight. The image is one of a number that were taken during testing and comes courtesy of Discover Magazine.
The AWT works under a similar principle as a wind turbine. Air moves across the turbine blades causes them to rotate which drives a generator for the production of electricity. The difference is the turbines are sent far higher than any tower-based turbine can reach with the flying height expected to be between 250 and 600 metres.
The goal of the company is to produce utility scale wind power using these AWTs in offshore wind farms.
Ampyx Power – PowerPlane
The PowerPlane system developed by the Netherlands based company Ampyx Power converts wind power to electricity through the pulling action of an unmanned glider on the tether that has it anchored to the ground. The glider operates at a height of 300-600 meters and performs cross-wind patterns. The generation of electricity is at its maximum when the tether is fully extracted.
The problem of low wind or extreme weather conditions is handled by programming fully automated launch and landing processes into the system.
It is expected that the first commercial version of the PowerPlane will have a wingspan of around 16.5 meters and has the potential to produce as much electricity as an 850kW, 50-meter rotor diameter conventional wind turbine.
This concept will weigh significantly less than a traditional wind turbine, weighing only 120kg for the plane and 400kg for the tether.
Altaeros Energies Airborne Wind Turbines
Altaeros Energies is a wind company that was formed out of MIT and it is responsible for the design and development of the Altaeros Airborne Wind Turbine (AWT). The AWT is a helium-filled shell that supports a lightweight turbine which can be lifted up to 1,000 feet into the air. The lifting technology is adapted from aerostats: tethered blimps that have been used for decades to reliably lift telecom and surveillance equipment into the air for months at a time.
In 2012 the company completed testing of a 35 foot prototype version of its AWT at the Loring Commerce Center in Limestone, Maine. In this particlar test the device ascended to 350 feet where it produced (an unspecified amount of) electricity before descending again and landed in an automated cycle.
The Altaeros AWT prototype is fitted with a Southwest Skystream turbine which is surrounded by a fabric superstructure.
It is expected that this AWT will be able to be quickly and easily transported to its location on a docking trailer and that installation time would be performed in a matter of days rather than weeks.
In 2012 Altaeros Energies were the recipients of a Department of Agriculture Small Business Grant to develop its technologies up until 2014. The key research objective of this project is to develop and test a fully-functional AWT prototype that demonstrates its potential for commercial deployment.
Update (June 2014): With some recent funding the turbines, which are now called Buoyant Air Turbines (BATs), will be undergoing 18 months of testing in Alaska. Find out more about these turbines in the article titled High Altitude Wind Power: Alaskan Tests Planned for BATs.
Magenn Air Rotor System
The Magenn Air Rotor System (or M.A.R.S) is a floating wind turbine that uses a horizontal-axis turbine to produce electricity. The MARS device is kept airborne through the use of helium and with the help of a tether, is able to be raised or lowered to preferred heights as it captures the most ideal winds. The tether is also the means by which the electricity is transferred back down to the ground.
The rotation capabilities of the device creates the “Magus Effect” which is an aerodynamic phenomenon provides additional lift, keeps the MARS device
stabilized, positions MARS within a very controlled and restricted location. This effect also means that the MARS device will remain at maximum altitude rather than being allowed to drift downwind on its tether.
A more detailed explanation of the MARS Wind Power Anywhere™ solution along with many images and diagrams can be found by visiting the Nampet website.
The LadderMill Kite is an interesting departure from the other types of high altitude wind energy ideas in that it uses technology based around inflatable membrane wings with the energy produced through mechanical reel-out power. The infaltable membrane wing is connected to the ground by a traction tether and the power is produced by the reel-in, reel-out pumping action of the tether as the device is moved by the wind.
During reel-out the kite moves in a figure-eight pattern at high speed. The movement creates a high-traction force and this is converted to electricity by a drum and connected generator. At this point the kite is capable of producing 20kW.
When the kite reaches the end of its tether the kite is depowered and it rotates and aligns with the wind. The drum/generator acts as a winch and the kite is then pulled back into its starting position for the cycle to start over again. The reel-in process only uses a fraction of the produced energy that was generated during the reel-out process.
Testing and improvement have been in constant process since 2010 with more than 160 completed pumping cycles. Prototype models have been tested using versions with kites of 14, 25 and 50 m2 surface areas.
More information about the technology, research and testing progress made on an ongoing basis can be found by visiting the KitePower website.
Other ideas that have been suggested include the Hovering Wind Turbine that was developed by Briza Technologies and Flying Electric Generators (FEGs) created by Sky Windpower. The methods of putting devices high into the air where they may capture the higher wind speeds and harvest the energy that they produce continue to spark a great deal of innovation and require many more hours of testing and research.
Another unique concept has been developed and tested with a prototype system by NTS Nature Technology Systems. This system uses a kite that is tethered to a rail-based car. The kite drags the car around a closed circuit loop with the car linked to an electricity generator by a cable.
Relate Article: High-Altitude Wind Power: NTS Nature Technology Systems.
The chance to put wind power up and out of sight is a motivating reason to continue to push on with the development of this form of wind energy production and while it will not replace the existing ground-based wind power, it could become a valuable additional source of wind power.