High altitude wind power

A flight wind turbine is a wind power plant, which is in contrast to a conventional wind turbine not firmly anchored on a mast, but only by a tether to the ground and otherwise flies in the air. Flight Wind power plants can in this case be similar to a balloon lighter than air and float freely, or be like a dragon or Surfkite heavier than air and will be held by the buoyancy of the wind in the air.

Flight Wind power plants can advance to higher altitudes than conventional wind power plants. Winds at these altitudes of several hundred meters to several kilometers, are stronger and more constant, and the energy content is a multiple of that of ground-level winds. The winds aloft are the most concentrated form of renewable energy available worldwide Represents the existing flight for wind power plants wind potential ranging from theoretical to satisfy the total primary energy demand of mankind more than a hundred times.

Due to the high winds and the great wind potential that can be tapped with flight wind power plants, wind power plants, flight may be able to produce significantly less power than other renewable energy sources, according to some views, even cheaper than fossil energy sources.

Flight Wind power stations are built from lightweight materials and can be realized compared to conventional wind power plants with far less material per unit. In addition, many types of aircraft wind power plants are inherently scalable, so that the size limitations of conventional wind turbines of a few megawatts of power do not apply. Flight Wind power plants can therefore in principle advance in power units of fossil fired power plants of several hundred megawatts.

Despite these advantages and the associated potential of flight wind power plants in 2010, there are only a few experimental prototypes. In particular, the difficulties of automatic control in flight and during takeoff and landing have prevented mass production of aircraft wind power plants. In addition, there are uncertainties regarding the optimal type of flight wind power plants and the materials to be used. Worldwide, however, deal a growing number of research groups and companies to resolve these issues and the development of aircraft wind power plants. It should be pointed out that the realization of flight wind power plants, a variety of practical issues have to be solved, but there are no fundamental technical or physical barriers.

• 4.1 design and materials
• 4.2 Management and Control
• 4.3 generation 4.3.1 electricity in the air
• 4.3.2 Electricity generation on the ground

• 5.1 Airspace and collision hazards to aircraft
• 5.2 lightning and extreme weather
• 5.3 crashes
• 5.4 legal and operating license

From dragons to flight wind power plant - History of Flight wind power plants

Already in early times upper winds were isolated by dragons used for load lifting. The dragon was developed in Asia. It also people were lifted with dragons. This was done as entertainment, but also for military observations. Only about Marco Polo came the principle of the kite to Europe. Leonardo da Vinci proposed a dragon to cross a river to pull vehicles and to derive the energy of lightning.

Even before the invention of the motor vehicle kites were used for pulling carriages, as Benjamin Franklin, the drive also boats with the help of dragons. The dragon pioneer Samuel F. Cody crossed in 1903 with a boat drawn by a dragon the English Channel and presented in the same year to a record for the highest kite flying at 14,000 feet ( 4200 m). With the inventions of powered flight and the use of fossil fuels waned interest in the use of high-altitude wind to the oil crises of the 70s, which led to a renewed interest and several research projects. For example, the engineer ML Loyd has the energy studied in detail by kites. Due to the fall in oil prices in the 80s, however, these projects were in collaboration with other research projects in the field of alternative energies such as solar thermal power plants, experimental wind generators as the Growian etc. largely abandoned. From the 90s of the 20 century, the research and development focused on conventional wind turbines. It was not until the turn of the millennium, there was a renewed interest in flight wind power plants. Highlighted adding here is the German SkySails that has developed since the turn of the millennium with considerable effort, a system for saving fuel on ships with the help of self-sufficient maneuvering flight mats. This system has been installed to date ( 2010) to about 10 ships and is located in a very advanced stage of testing, without the production stage would have been reached so far.

From about 2005, shows by various of increased interest in flight wind power plants to generate electricity. Among others were missing until recently, various technologies for the development of flight wind power plants, also seemed to conventional wind turbines to push the technical limits. Only by developments in the field of sensors, materials, computer-controlled autopilot etc. of the construction and operation of flight wind power plants appear to be feasible. A variety of university research groups as well as non-academic start-ups have been dealing this time with the development of flight wind power plants. It also increased private lenders are aware of the potential of these technologies. So the company Makani has been able to collect about $ 30 million from an affiliate of the Google Group to develop a flight wind power plant. Besides a large number of patents and publications in this area annual international conferences are held to flight wind power plants from 2009. It was also established with the Airborne Wind Energy Consortium, an international organization of companies active in this area.

Despite these efforts and successes has not been able to 2009 the completely autonomous flight operation of an aircraft wind power plant over several days with autonomous takeoff and landing.

Flight potential of wind power plants

Conventional wind turbines are limited to the use of the near-surface wind, the hub height of the wind turbines and the rotor diameter limits the maximum amount of usable wind. The existing in 2010 conventional wind power plants can utilize winds up to around 200 m above the ground.

The average wind speed increases with the distance from the bottom. By the ground-based friction of the wind is slowed down near the ground. On rough ground surfaces such as hills, forests or high buildings, the braking effect is stronger than the case of smooth floor surfaces ( lake, ocean, flat country with low vegetation). The influence of this braking effect of the ground surface to the wind is reduced with the distance from the ground surface. This wind speed increases with height up to about 10km altitude. At this altitude occur the so-called jet streams with peak wind speeds of up to several hundred km / h in the temperate latitudes. The average wind speed at the bottom is about 5 m / s, while it is 40 m / s in the jet stream.

For the use of wind energy is the wind speed of fundamental importance. The useful energy increases not only linearly with the wind speed, but also increases with the cube of the wind speed. This means that a doubling of the wind speed, the energy contained in the wind increased eightfold, with a tripling of the wind speed it takes about 27 times to. The average energy density in the jet stream at 40 m / s wind speed is not only eight times as high as on the ground with 5 m / s wind speed, but is 512 times the energy density of the near-surface wind. This potential can be calculated using a recently published global atlas to the energy density of the upper winds at different heights between 80 m and 12,000 m appreciate good .. To be considered, however, that at higher altitudes the air density decreases, the usable energy in turn reduces and the higher wind speeds, the stresses on the plants grow.

Flight Wind power plants can also be operated within their maximum design maximum height in different changing heights. Thereby, the height can be changed at low wind at a certain height. In addition, can be used from a single location, the wind power from different heights, so that the usable unlike conventional wind turbines wind power per unit area multiplied. This could be achieved on a small floor area considerably higher amounts of energy, land use and the impact on the landscape would therefore be lower.

The higher wind speeds at higher altitudes also means higher utilization of wind turbines. Thus, the capacity factor is conventional onshore wind turbines, depending on location, on average, about 30-40 %, while projections for high-altitude wind turbines of up to 80 % utilization out. This effect would improve the consistency of wind energy and alleviate a major problem of wind energy use. The associated forced to Provision of alternative power sources, mostly from fossil fuels like coal and natural gas would be defused. Also could possibly electricity generation costs decrease due to the higher utilization of power plant. As yet there are no commercial flight wind power plants, but no real data is available.

Due to the higher average wind speeds and reduced dependence on the soil characteristics and the strength of the surface winds altitude wind power plants can also be unsuitable for conventional wind power plants locations, such as in low-wind inland, are operated. Locations for wind power plants could thus depend on the power consumption in the region and less by the wind speed on the ground. Thus the space required for the conversion of energy to wind energy expenditure for network expansion itself could decrease. This requires about Germany in the transport of wind power from the strong wind producing regions in the north to the consumption centers in the central and southern Germany. Note, however, that flying wind turbines have significantly greater impact on the flying, making these investments in certain areas can not be built.

Estimates assume that producer prices of less than 1 Euro cent per kw / h of electricity up to 2 cents per kw / h of electricity could be realistic. If this assessment proves to be correct, flight wind power plants would not only be by far the cheapest source of renewable energy, but also cheaper than fossil power plants, even without taking into account external effects such as CO2 emissions.

Design principles of flight wind power plants

To achieve the upper-level winds, the flight wind power plant is not fixed, in contrast to conventional wind turbines on a tower or mast. Buildings with a height of several hundred meters or even kilometers are not, or not to create a reasonable cost.

Flying wind power plants are based on that the support surface is only supported by a rope or cable. The flight wind power plant fly on this cable because it is lighter than air or held by the buoyancy of the wind in the air.

Lighter than air

This is a task to distinguish between balloon-like, filled with light gases and thus floating without dynamic lift flight wind power plants, which are lighter than air. An example of such a concept is the flight windmill of the Company Magenn. This is a rotatably mounted about the longitudinal axis of elongated balloon like an anemometer or Savoniusrotor rotates thanks attached to the longitudinal side curved slats around the longitudinal axis and so drives a generator.

Heavier than air

The alternative flight are wind power plants, which are heavier than air. These convert a portion of the wind energy into dynamic lift which keeps the aircraft wind power plant as a kite or kite sailing in the air. These systems provide a considerably higher demands on the controller because a controller error usually leads to a crash.

The proposed systems continue to differ as to whether the electricity in the air takes place and is then transmitted via cable or wirelessly to the ground or if the energy is transferred mechanically to the generator at the ground station. Other types of conduct the kinetic energy about by ropes or chains to the floor. The generator produces electricity then on the ground.

Furthermore, a distinction between power plants, flying stationary over one place or float, as well as between power plants, thereby increasing the energy yield that they quickly cross-wind to fly (Cross - Wind Power), such as in a circular motion or in the form of an 8 These maneuvers, which are also used in kitesurfing, increase the area swept by the wing surface, the relative wind speed on the wing and can be used by the power plant wind power. The principle behind it can be explained well by a comparison with conventional wind turbines. In these, the tips of the wind turbine to generate a large part of the total energy of the system. This is because these peaks extremely fast turn in a circle and thus sweep over a large area. The wind is decelerated to the total swept area and not only on the circular section, on which the wings is straight. Designers of such fast-flying airplane wind power plants have the goal of reducing the wind power plant on these effective, then flying parts, and sacrificing the heavy and expensive remaining structural components such as the leaf centers, the hub and the mast.

Constructive differences of flight wind power plants with conventional wind power plants

Design and materials

The flying part of a flight wind power plant must be built easily. To make this not only the choice of textile and flexible materials, are also to choose designs that erode material in its most advantageous way. This means that as only tensile and compression forces but hardly heavy forces should act on the individual components as possible. In conventional wind turbines but just these lateral forces dominate, so that the towers, rotor blades etc. must be extremely stable dimensioned to withstand these lateral forces can. Thus, the required mass of these components increased many times over.

Heavy forces anchoring ropes, as is the case with the kite can be almost completely avoided. Increase, however, bracing air resistance considerably. As far as the power output is to be increased by rapid flight, but you have to keep to a low drag at high buoyancy of a high glide ratio. Therefore, one of the challenges of the construction is to achieve sufficient stability for the structure of the supporting surface with a low weight and yet a low air resistance. For about inflatable structures with internal tension cables such as Tensairity ® can be used.

However, even with commercial Surfkites that are not aerodynamically optimal, been considerable achievements of 30 and 40 kw calculated or obtained.

Dyneema ® is used for the ropes mostly, with new materials such as nanotubes could dramatically increase the performance and capabilities of flight wind power plants.

Management and Control

The autonomous flight control of wind power plants and the fact that they fly contrary to conventional wind power plants anywhere in the room, is one of the key challenges in the development of flight wind power plants dar. Existing developments are primarily failed because of this problem. A variety of sensors to measure as many parameters (wind speed and direction, position, velocity relative and absolute movement direction, wire tension, vibrations, etc. ) must be forwarded to an autopilot, which then control software performs the correct steering maneuvers. The software must be such that it allows a safe flight as possible, whilst promoting the highest possible energy production. Thereby represent sudden and unforeseen changes in wind speed and direction, a particular problem dar. challenges also exist in the takeoff and landing phase, possibly an entirely different flight movement to normal operation is required.

Lack of opportunities in the field of sensors and computational resources presented in earlier times one of the biggest obstacles in the construction of wind power plants Flight dar. In recent years, a variety of progress has been made ​​in this field, however, so that now appropriate sensors are available at low cost. Meanwhile, mobile phones are equipped as standard GPS sensors or even position sensors (about IPhone and Wii controller ) itself.

The actual flight control is performed either as a plane through various attached to the flight wind power plant ( height, lateral, transverse ) rudder, or according to the control with kites and kites by shortening the steering cords and ropes, and thus by a change in employment of wing or the kite. In the latter variant in each case all control cables can either be performed from the wing to the ground station, which is then to be expected with appropriate cable length with increased air resistance and for delayed response and less precise steering instructions. An alternative is to merge the steering cables on a steering module under the wing. The further connection to the base station would then be carried out via a single cable. The steering module would then have to carry out the steering movements but have a power source. This would have about using batteries in a place in the power cord or rope built by small wind turbines on the wings that create the work flow.

Power generation

Basically, the power generation can be carried out in the air or on the ground station.

Electricity in the air

To generate electricity in the air basically the heavy power generators must be carried in the air. Secondly, current leakage to the ground station must be done. Usually via a cable incorporated in the power line occurs.

It could mean electricity in the air by flying wind turbines. The lack of anchorage can be replaced by two counter-rotating wind turbines or on a shaft such as by a plurality of smaller turbines that are held by a frame. The latter approach is followed by Skywindpower whose prototype has four helicopter -like rotors.

The electricity in the air can alternatively be performed by a small, vertically mounted like an airplane wing for propeller attached generator. The wing while flying fast circular movements and is braked by the drive of propeller and generator. This concept largely corresponds to the implementation of autonomous blade tips of a conventional wind turbine. Only the deceleration is not performed by driving the central hub of a wind turbine, but by the small propeller on the wing. Both Makani and Joby Energy follow this principle.

One advantage of most of these designs is that the generator during a lull, and for takeoff and landings can be used as a motor. The proposal of Makani and Joby Energy looks off and landing like a helicopter before, with energy being expended. With this option, the start and the safe landing during a lull possible is self-sufficient in these variants. In addition, an increased maneuverability increases in some variants by the possibility of controlling various motors similar to a mehrrotorigen helicopter. In air the above-described circular motion is then performed to generate electricity.

Through the power line in addition to the ground power supply to the sensors and control of the wing is secured.

Electricity on the ground

When electricity is generated at the bottom of the generator is in the ground station. Energy mechanically, usually by means of cables is transmitted from the airfoil to the ground station.

The most favored variant is the so-called yo-yo configuration. Here, the lift generated by the wings is used to pull the tether. The tether is released slowly and thereby drives the ground station via a cable drum a generator. Once the final position is reached, the rope under expenditure of energy must be recovered. Here the wing is placed so that it has the lowest possible air resistance and therefore much time and energy is required for recovering the rope. Then the cycle begins again.

Other alternatives require that the kinetic energy is transferred by a rapidly rotating tether, which thus serves as a shaft to the ground.

The laddermill mentioned proposal of the former Space Shuttle astronaut Wubbo Ockels, provides for a power transmission similar to a bicycle chain, a circular tether ago, in which several wings are evenly distributed. While located on the windward side of the rope wings are placed so that they generate lift and drag one end of the rope to the top, the other wings are neutral set, so that they produce the least possible resistance at the drop. At the ground station equipment mentioned the ever-churning rope in turn drives a generator.

The advantages of the power generation at the bottom are the potentially lower weight and potentially lower the complexity and cost of the airfoil. Crashes and wear would thus cause lower costs. The ground station with the generator of a yo-yo configuration could be used also with new technologies in Tragflügelbau. You may also conceivable, depending on the wind situation Hydrofoil to use with different size or aerodynamic properties or to drive the generator with more caps in weak winds. The disadvantages are seen in the need for wing energy supply as well as the inability of the autonomous takeoff and landing by helicopter principle.

Challenges in the development and operation of wind power plants Flight

In addition to these currently unresolved technical issues, there are also other areas of conflict for the realization of flight wind power plants.

Airspace and collision hazards to aircraft

Flight wind power plants can be operated well above the air space of 100m height beyond, for which there is market competition and risk of collision with aircraft. This is mainly a competition with the private flying for the use of up to 1000 m. To ensure the security of private flying should be established on the site of flight wind power plants fly zones to ensure, as they now existed for over nuclear power plants and other built-up areas. In the relatively low operating life of the installed Skysail drives a near- collision has taken place with a helicopter.

Lightning and extreme weather

The long tethers represent excellent conductor, is likely to result in increased thunderstorms with lightning strikes. Here, however, it seems to be possible to make appropriate insulation of the wing and the ground station against lightning. Furthermore, flight wind power plants can also be landed with appropriate weather conditions.

This raises the question remains whether in cold weather the wings icing is a major problem. Furthermore, the question arises how quickly the lightweight materials and the ropes used in continuous operation wear out and must be replaced.

Crashes

It is to be expected due to the complex control of flight wind power plants, which are heavier than air, at least in the test phase with increased crashes. Even with sophisticated systems to crashes can probably not be excluded with absolute certainty. Therefore, flight wind power plants are expected only in such locations in question come where a risk to humans is excluded.

Legal and operating license

Exist for the construction and operation of wind power plants flight in 2010 for Germany no specific legal regulations. Construction ( planning ) law and aviation law permits should be obtained only with considerable effort by individual decisions.

Projects

While other versions of the flying wind turbines are becoming increasingly technical maturity, a use of the jet stream according to the above principle does not seem tangible. Today's systems operate with cable lengths of several hundred meters and altitudes 300-500 m ..

The European developments such as the Brandenburg EnerKite, which also Brandenburg company NTS, the University of Delft in the Netherlands, and the Italian company Kitegen deal with kites, which drive generators located at the bottom. ,. EnerKite has taken on March 23, 2012, a mobile air wind turbine with a rated power of 30 kW in operation, serving the technology development and demonstration.

Another, also a kite similar concept was developed by the Californian company Joby Energy .. This development continues, also from California company Makani and now presents a 30 kW system with a propellierten 8 meters wide wings. Here the energy is converted by wind generators on the wings in the air and passed with high voltage by a rope of constant length to the ground ..

A lighter- than-air concept Atena Engineering has developed. These are investments that float relatively low at a height of several hundred meters. The arrangement of the rotors is quite close to that of a conventional wind turbine, resulting in a comparatively high efficiency means. The main advantage to such systems is the reduction of critical loads in large to very large diameters of 100 to 300 meters.

NASA also explores the possibility of flying wind turbines.