Wind power is currently the fastest growing renewable energy source. Wind turbines are constantly getting taller because everyone knows the higher you get off the ground, the stronger the wind speeds and the more power that can be obtained. At higher altitudes, wind is also more constant. However, building big towers is not only very expensive, but also not possible due to the weight of the tower. This is where kites come into play.
by Aysu Katun, Green Economy Post
Most of us have probably heard that kites were invented by the Chinese or seen fascinating sights from kite festivals throughout the world. Since their invention, kites have had many uses besides looking pretty in the skies. They have been used for military signaling, radio experiments, hunting and meteorology. Since the 1990s kites have been used in extreme sports like kite-surfing and kite-skiing. What some of us may not know is that kites may also be the future of power generation.
It is estimated that about two percent of the Sun’s energy that arrives on the earth’s surface is transformed into wind energy and that this mere two percent is more than enough to cover our energy needs. The total energy stored in the form of winds is estimated as of the order of 2000 TW (Hurley 2009). In comparison, the total primary energy generated by humans corresponds to an average of just about 16 TW.
Wind power is currently the fastest growing renewable energy source (solar has a faster percentage growth rate in terms of capacity). Wind turbines are constantly getting taller because everyone knows the higher you get off the ground, the stronger the wind speeds and the more power that can be obtained. If, for example, wind turbines could be raised to a height of 800 m, the power obtained could be increased by a factor of 8 in comparison to the same turbine near the ground. At higher altitudes, wind is also more constant. However, building big towers is not only very expensive, but also not possible due to the weight of the tower. This is where kites come into play.
Proponents of airborne wind power like Ken Caldeira at the Carnegie Institution Science’s Department of Global Ecology say that if we could tap into one percent of the energy in high-altitude winds, it would be sufficient to provide all our power needs. There are many ideas in the field, but there are three companies that have been able to create promising systems that have been studied in depth and tested in practical experiments.
Kite Gen
Researchers in Italy have come up with a simple and innovative concept: the Kite Wind Generator, or Kite Gen for short. Kite Gen uses state of the art kites. In the basic configuration, called the “Kite Gen stem”, the system uses a single kite linked to a power generator located on the ground. The kite moves like a yo-yo: when it goes up, it generates energy that is transformed into electric power by the generator. When it reaches its maximum height, it is placed in an aerodynamically non-lifting configuration, so that it can be pulled down at a very small energy cost. A control system on autopilot optimizes the flight pattern to maximize the power generated and a radar system can redirect kites within seconds in case of any interference such as small planes or even single birds.
Research by Sequoia Automation, the small company heading the project, estimates that Kite Gen could generate one gigawatt of power at a cost of just 1.5 euros per megawatt hour, which is nearly 30 times less than the average cost in Europe of 43 euros per megawatt hour. Proponents claim that Kite Gen can produce as much energy as a nuclear power plant. It is also claimed that Kite Gen eliminates all the static and dynamic problems that the traditional wind turbine generators have. Other potential advantages of the Kite Gen system include cheaper building and installation costs and limited amount of space needed compared to traditional wind farms. The system could also provide wind-based power in areas where traditional wind farms are impractical because of terrain or land use limitations.
Kite Gen’s first prototype was built in 2006 and received positive results. The first full-scale system is a 3MW generator, which is expected to begin operating in late 2009. Proposed future systems include off-shore generators, and “carousel” arrays of multiple kites that could theoretically produce over 1GW of power output.
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Laddermill
Wubbo Ockels, a professor of sustainable engineering at Delft University of Technology in the Netherlands and former astronaut is leading the Laddermill project. The Laddermill consists of a series of wings or kites all connected to a cable that forms a huge loop. The kites would be computer-controlled to change their altitude and generate more lift from the wind on one side of the loop than the other. This would cause the entire loop to rotate, and its rotation would push a generator down on the ground to create electricity. Ockel’s system uses these flying patterns to maximize the power the kites can generate.
His team is building a 100kW prototype. He hopes to start testing a full-scale device, which would generate 10MW, within five years. That would be large enough to power around 10,000 homes. He believes the system should be capable of generating electricity at a cost of just 1 cent a kilowatt-hour. This system has the advantage of requiring only simple parts, generators, kites and cables and should be much cheaper to build than a conventional turbine.
Makani Power
The entrepreneur behind Makani Power is Saul Griffith. Google.org, the philanthropic arm of the Californian web-search company, invested $10m in the US kite company. Makani is the least transparent of the airborne wind power companies. It has only revealed that it is building huge wing-shaped kites to harness the energy from high-altitude wind. In a talk he gave at Technology Entertainment Design (TED.com) in February 2009, Griffith said that Makani has tested kites “generating 10 kilowatts – enough to power 5 US households” and that they are “working towards megawatt scale machines that fly 2000ft” and are “developing control systems that would enable sustained long duration flight.”
While all of these systems look promising, high altitude power generation has several drawbacks. One drawback mentioned by scientists is that in the long term, trying to power entire cities with systems like this would be difficult because even in the best locations, the wind will fail at least 5 percent of the time, which means that there will be a need for either backup power or a continental scale electricity grid to assure power availability, which requires substantial investment in infrastructure.
Another problem could be the effect of high altitude kites on the atmospheric wind circulation. This problem has been examined by Archer and Caldeira (2009) by means of climate models. The results are that tapping high altitude winds would reduce precipitation and that it would have a cooling effect and could affect climate. The problem would be minimal (around 0.1% reduction in precipitation) for the amounts of energy tapped corresponding to our present demand, but this effect does pose a limit to the technology.
Even in the face of these drawbacks, kites offer us a hope of a future of abundant, cheap and clean energy, which is why, even if these ideas may seem crazy or farfetched to some, they need to be supported if we are really serious about renewable energy sources.
For alternative technologies that harness high altitude wind power, see Sky Windpower and Magenn Power as well.
