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PrintJoe Hadzicki & Dave Lang
From Discourse 9
Allen Ibara, Joby Energy
Allen Ibara, Joby Energy
INTRO TO HIGH ALTITUDE WIND ENERGY JOE HADZICKI
Let’s do a quick overview of the subject of high altitude wind energy. In a nutshell, the industry is attempting to extract energy from the wind at higher altitudes than a wind turbine. Ground based wind turbines are limited to around 300 feet. As you increase altitude, the wind speed also increases. The “pie in the sky” goal would be the jet stream (30,000+ feet) since the sustained wind speed can easily exceed 100 MPH, occasionally reaching speeds in excess of 200 MPH. But this introduces several problems such as equipment, weight, safety, and not least, permission from the government, which seemingly for the near future has directed most efforts to the one to two thousand foot altitude range.
Now let’s consider three main variables: lift device, generator location, and flight path. The industry combines these variables in various combinations resulting in the current designs presented at the conference.
Lift Devices
Generally speaking, three different types of lifting devices are currently being used to access higher altitudes:
- Aerodynamic lift using kites or rigid aircraft style wings
- Aerostatic lift using aircraft similar to blimps
- Rotorcraft using devices not unlike helicopters
Generator Locations
Generators are used to convert the motion produced by the wind to electrical energy. These generators can be carried on board the flying device or located on the ground.
Flight Path
The flight path of the various designs differ in two ways: “reeling out/reeling in” motion, and “cross-wind” flying motion. The devices with on-board generators can be reeled out to the working altitude where they operate for extended periods, from hours to days or hopefully longer. They are then reeled in in response to weather conditions, maintenance, etc. Devices with ground based generators use a yo-yo type of motion to collect energy. As the wind pulls these devices out, the tether spins the ground based generator, which produces power. Some of this power is then used to reel the device back in. The process is repeated for the duration of the energy harvest period.
The second flight path used is called “cross- wind” flying. Cross-wind flying is a technique to increase the power output when flying. As the lifting device is flown across the wind, the apparent wind (the wind flowing over the wing) is moving faster than the ambient wind speed. Since the power generated by the wing increases as the cube of the wind speed, cross-wind flying can greatly increase the power output of the flying device. For example, using the cross-wind flying technique to double wind speed increases the power eight times!
REFLECTIONS ON THE CONFERENCE DAVE LANG
It is indeed exciting to be aware of, and involved in, the new potential industry we refer to as Airborne Wind Energy (AWE). It is particularly charming that it has been spawned by, and some AWE incarnations may well feature, wind harvesting that utilizes the age-old kite. However, that said, there are many other ways being proposed to accomplish AWE harvesting, and the ultimate winners are yet to emerge. More specifically, AWE transcends “soft kites,” and now employs schemes that use “wings” or “lifting rotors” carrying aloft wind turbines, which themselves (being rotors) can become involved with not only electrical generation, but also in producing useful lift. Most combinations of the above are now being examined actively.
When it gets down to brass tacks, AWE is a highly technical field, because we find ourselves using aeronautical schemes, wind turbine technology, high-tech materials, meteorology, and abstruse analyses required to not only simulate flight and control dynamics of tethered lifting devices, but also to arrive at meaningful estimates of yearly power production that rigorously factors in the statistics of wind. As in other fields of intense scientific/engineering endeavor, these technical challenges of course lead folks to want to congregate and consort with one another to discuss methods and findings.
So, as all new industries are inclined to do, the periodic “gathering of the clan” (i.e. industry conference) is a ceremony of importance since it brings folks of like mind together to jovially stimulate and ridicule, encourage and criticize one another towards their mutual goal. I have now attended all three conferences in the US related to this emerging field of AWE. First, there was the 2006 Kite Sailing Symposium sponsored by the Drachen Foundation (possibly the “original” AWE conference, since many attendees were there to exchange information on traction kite technology as it might apply to wind power harvesting). Next, the 2009 High Altitude Wind Power Conference (the first official high altitude wind power conference) sponsored by California State University Chico, BayTEC Alliance, and Cleantech Innovation Center of Oroville.
I have noted a significantly increasing level and diversity of attendance and interest in these conferences.
So now, the third such conference has been attended, namely, the Airborne Wind Energy Consortium (AWEC) conference held on the Stanford University campus on the 28/29th of September 2010. This was the first public event officially orchestrated by the AWEC, a consortium of AWE developers in this newly emerging field who have figuratively circled their wagons to provide a form of industry- conventional unanimity. By the way, I emphasize that the term “Airborne Wind Energy” (AWE) is used to set apart this new field from the more conventional wind- power industry that is largely (and historically) dominated by the ground based, tower-mounted, Horizontal Axis Wind Turbine (HAWT).
I attended the conference as a representative of the Drachen Foundation, since, for a number of years, I have been a Drachen board member and their point of contact/clearing-house for those approaching Drachen seeking information related to AWE. Of course, AWE schemes based on traction kites (which are commonly exhibited in the somewhat ubiquitous sport of kite surfing and kite sailing) are a stalwart component of Drachen’s kiting interest and history.
The 2010 AWEC conference listed over 80 organizations attending, which correlated well with my estimate of the total attendance pushing 150 people. The conference featured a fairly conventional array of general presentations given more or less to the entire attendance in the morning sessions and regarding subjects that are common to all who are involved in AWE (regardless of engineering approach), such as safety, liability, reliability, geo-wind characterization, airspace clearance, business capitalization, etc. Mixed in with these were presentations given by the representatives of specific development groups and companies, outlining their conceptual approach to AWE, as well as their state of progress. Finally, for the second portion of the daily fare (with some concurrency with the more general presentations), there was a “dual track” presentation plan set up which featured technical presentations related to methodologies ranging from simulation analysis and detail results, to new and novel AWE schemes, to the application of generic mature technology disciplines, to the engineering design of AWE.
I observed this 2010 AWEC conference to be more nearly in line with traditional technical conferences I have attended over a period of 40 years in the “mature technical fields” (specifically, aerospace and aeronautics). That said, there was still a notable lack of the core middle-aged and older industry-experienced attendees and academics that are usually found in abundance at technical conferences related to more mature technologies. I would anticipate that this will change with the natural evolution of the AWE field. It is important to this emerging field that it exhibit on an ever more “professional persona” to attract investment and high quality experienced engineering talent. So I would say the AWEC 2010 conference moved closer to attaining such a goal.
The originators and sponsors of this event did a nice job of arranging excellent facilities and meeting venues (how could you beat the Stanford campus as a venue?). There were about the right amount of communal meals and casual break time (with snacks and libations) to promote a nice level of networking and technical discussion. Audio/visual support was well orchestrated by the technicians, and presentation flow went smoothly.
Of particular note was the participation of representatives from the US governmental agencies, NASA, ARPA-E, NREL, and FAA. Furthermore, there was a surprising number of attendees from other nations represented: Denmark, Italy, Germany, United Kingdom, China, Korea, Belgium, Germany, Switzerland, Netherlands, and Canada. Many foreign nationals provided interesting presentations. It is apparent that AWE is attracting a lot of interest world-wide, and competent technologists are starting to take note.
There is still a conspicuous absence of successful AWE deployments in terms of harvesting significant amounts of wind power. Moreover, one of the major bugaboos in AWE is autonomous launch and retrieval, and while many claim to have solved this problem in principle, there was a notable lack of examples or data (for even prototypes) showing actual operation of deployed AWE systems for days on end through excessive wind and/or no wind conditions. This is clearly a hurdle that everyone is struggling with, and the winner(s), if their attendant configurations can produce economically viable power, will surely be in line for a healthy future.
I could not conclude these impressions without noting the presentation made by Miles Loyd, whose 1980 seminal paper about “Crosswind Kite Power” represents possibly the first analytical formalization of the phenomenon and flight-maneuver known to virtually all traction kite sportsmen. Loyd’s paper is referenced by most developers in the field of AWE. It was a nice piece of closure to see Loyd addressing a conference audience, most of whom were standing high upon his shoulders from an historical standpoint.
All in all, it was a pleasant three days on the Stanford campus, meeting many with whom I have only had email correspondence, getting acquainted with our international AWE brothers and sisters, and coming away with a sense that the AWE endeavor is being furthered by a nice group of serious, dedicated developers who not only strive to perfect their technology, but also to improve the human condition through the use of airborne wind power.
CONFERENCE PRESENTATIONS JOE HADZICKI
Miles Loyd
It’s fitting to start out the list of presenters with Miles Loyd. Considered by many as the father of cross-wind power. His original paper titled “Crosswind Kite Power,” published in a 1980 issue of Journal of Energy entails the physics involved in harvesting high altitude wind energy. His 1981 US Patent #4,251,040 proposed design uses a tethered airplane with on- board, propeller-driven generators. Miles also employs the cross-wind flying technique outlined in his paper to increase power generation. The power is then transferred to the ground using a power cable/tether.
Joby Energy
http://www.jobyenergy.com
One of the Joby designs uses an aircraft style platform tethered to a tower. As with Miles Loyd’s design, high speed air flow from the wind flowing over the wings generates lift to propel the plane. The propellers are used as spinning generators, which convert the wind energy to electricity that is transmitted to the ground by the tether/power cable. The plane flies in a large circle that is a form of cross-wind flying. Joby claims a working prototype that produces power in the 5 kilowatt range. Their current focus is to attain complete autonomous flight from launch to landing. A video was presented at the conference showing autonomous launch and transition to autonomous flight control. Landings are still assisted.
Makani Power
Makani Power uses a similar process of a rigid airplane wing as the lift device. On- board generators, spun by propellers, then transmit power to the ground.
Ampyx Power
Ampyx Power, located in The Netherlands, uses its PowerPlane airplane design with a ground based generator. Ampyx employs the cross-wind flying technique to increase power generation in conjunction with the yo-yo method to collect energy.
Aeroix
http://www.aeroix.de/en/projects
swisskitepower
http://www.swisskitepower.ch
Kitenergy
Aeroix, swisskitepower, and Kitenergy uses a similar approach to Ampyx but replace the airplane device with a kite. A kite is used as a lifting device. The generator is ground based, and a cross-wind flying technique is used in conjunction with the yo-yo method to collect energy.
MagGenn
http://www.magenn.com
MagGenn uses a helium filled, blimp-like lifting design that has inflated turbine blades that spin in the wind, producing power. A stationary framework containing the spinning blimp has an on-board generator which collects the power and sends it by power cable to the ground. See a video: http://www.youtube.com/watch?v=JDJhhGJwSuA
Altaeros
Altaeros was formed by a team of students f rom Harvard and MIT. Based on surveillance blimp technology, their design uses a helium filled “ring wing” as the lifting device. Contained within the ring is a wind turbine. Altaeros’ goal is to reduce the cost of offshore wind energy by 60% compared to standard offshore wind turbines.
SkyMill Energy
http://www.energykitesystems.net/0/SkyMillEnergy/index.html
SkyMill Energy uses an auto gyro connected by tether to a ground based generator. In high winds, the gyro spins and generates lift which pulls the tether out. As it reels out, the tether spins the ground based generator which produces power. SkyMill’s design uses cross-wind flying motion to increase the available power. The SkyMill design also uses the yo-yo method to increase available power. For the reeling in portion of the yo- yo cycle, the propeller blade angles are changed, decreasing the drag. One of the big advantages of the auto gyro design is that they are very stable in gusty winds since the gusts are very small compared to the speed of the rotor.
Sky WindPower
Another company, Sky WindPower, is also using an auto gyro. In contrast to SkyMill Energy, their generators are on-board and transmit the power to the ground through a tether/power cable combination. Sky Wind Power eliminates the need to continuously yo-yo the system since the generators are on board. But they add weight and complexity due to the on-board generators and the weight of the power cable.
Windlift
Windlift currently uses a kite surfing style kite as its lifting device, tethered to a ground based generator. They employ the yo-yo reel method along with the cross-wind flying technique to increase apparent wind, resulting in higher power output. Its system is housed in a trailer and is designed to be mobile for use in remote locations. There are several obvious advantages with this approach. They can easily trade out lifting devices as technology evolves. The kite lifting device is low cost and easily changed out. Maintainability in the field is easy and low tech. It’s also relatively safe since the on-board weight is by far the lightest of all the current designs.
Although the designs and strategies are varied, one thing is for sure. This is a passionate and highly motivated group of entrepreneurs. Time will tell which approach will win out.