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Airborne wind turbine [ Edit ]
An
Airborne wind turbine is a wind power plant, which is not anchored in
contrast to a conventional wind turbine on a tower, but only by a guy
on the ground and otherwise flying in the air. Flight wind power
plants can thereby 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
turbines. Winds at these altitudes of several hundred meters to
several kilometers are stronger and more constant and the energy
content is many times that of near-surface winds. The upper-level
winds are the most concentrated form of worldwide availability of
renewable energy. [I] The existing Aviation wind turbines wind resource
could theoretically sufficient to satisfy the total primary energy
demand of humanity more than a hundred times. [Ii] Due to the high
winds and large wind potential that can be developed with flight wind
power plants, wind power plants flight should be able to produce
considerably less power than other renewable energy sources, according
to some views, also cheaper than fossil energy sources. Flight
wind power plants are built from lightweight materials and can be
realized compared to conventional wind power plants with much 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 not apply. Flight wind power plants can
therefore in principle advance in power units of fossil large power
plants of several hundred megawatts. Despite these advantages, and
the associated potential flight wind power plants in 2010, there are
only a few experimental prototypes. In particular, the problems of
automatic control in flight and during takeoff and landing have
prevented mass production of airplane wind power plants. In
addition, there is uncertainty regarding the optimal type of flight
wind power plants and the materials to be used. Worldwide,
however, employ 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 to be resolved, but
there are no fundamental technical or physical obstacles.
From the Dragon to the Airborne wind turbine - History of Flight wind power plants [ Edit ]
Already
in early times winds aloft were isolated by dragons used to lifting
process. The dragon was developed according to our findings in
Asia. This also people were lifted with dragons. This was
done as entertainment, but also for military observations. [Iii] Only
about Marco Polo was the principle of the kite to Europe. [Iv] Leonardo
DaVinci beat a dragon before to cross a river to pull vehicles and the
energy of dissipate lightning. Before the invention of the
automobile kites were used for pulling carriages, as Benjamin Franklin,
the drive also boats with the help of dragons. [V] The dragon pioneer
Samuel F. Cody crossed 1903 one of a dragon-drawn boat the English
Channel and set in the same year a record for the highest kite flying
at 14,000 feet (approx 4200 m). [vi] With the inventions of powered
flight and the use of fossil fuels waned, interest in high-altitude
wind utilization to the oil crises of the 70s, the led to a renewed
interest and various research projects. For example, the engineer
ML Loyd has the energy studied in detail by kites. [Vii] Due to the
decline in the 80s and 90s oil prices these projects, however, were
jointly with other research projects in the field of alternative
energy, such as solar thermal power plants, experimental wind
generators as the GROWIAN etc. largely abandoned. From the 90s of
the 20th 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. Achievements
have here is the German Skysails AG, which has developed since the turn
of the millennium with considerable effort, a system to save fuel on
ships using self-sufficient maneuvering flight mats. This system
was installed to date (2010) to approximately 10 boats and is located
in a very advanced trial stage, without the production stage would have
been achieved so far. [Viii] From about 2005 shows from various
quarters increased interest in flight wind power plants to electricity
generation. The reasons for this seem to be the one the emerging
limitations of conventional wind turbines. Thus, in countries such
as Germany prime areas for wind power plants are scarce. In
addition, the size and power growth pushes conventional wind turbines
limits. With a capacity of 5-7.5 MW a technical and economical
limit seems to be reached. On the other missing until recently,
various technologies for the development of flight wind power
plants. Only by developments in the field of sensors, materials,
computerized autopilot etc. of the construction and operation of flight
wind power plants appear to be feasible. [Ix] A variety of university
research groups and non-university 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 by a subsidiary of Google Group to develop a flight wind
power plant. [X] In addition to a large number of patents [xi] and
publications in the field are held from 2009 annual international
conferences on flight wind power plants . [xii] It was also established
with the Airborne Wind Energy Consortium, an international organization
of enterprises operating in this area. Despite these efforts and
success until 2009, the fully autonomous flight operation of an
aircraft wind power plant over several days with autonomous takeoff and
landing failed. [Xiii]
Potential of flight wind power plants [ Edit ]
Conventional
wind power plants are limited to the use of near-ground wind, the hub
height of the wind turbine, and the rotor diameter limits the maximum
amount of usable wind.Existing in 2010 conventional wind power plants
can use up to a maximum of 200 m above the surface winds (largest wind
turbine Enercon E-126 with a hub height of 135 m rotor diameter of 63.5
m, total height 198.5 m). The average wind speed increases with
the distance from the ground. Due to the ground friction of the
wind is slowed down near the ground. On rough floor surfaces such
as hills, woods or tall buildings, the braking effect is stronger than
on smooth floor surfaces (lake, sea, plains with low
vegetation). The influence of this braking effect of the ground
surface on the wind decreases with the distance from the soil
surface. This wind speed increases with height up to about 10 km
altitude. At this height, the so-called jet streams occur with
peak wind speeds of up to several hundred km / h in temperate
latitudes. The average wind speed at the bottom is about 5 m / s,
while it is 40 m / s in the jet stream. [Xiv] eightfold in a tripling
of wind speed it takes around 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 at the bottom with 5 m / s wind speed, but is 512
times the energy density of near-ground wind. This potential can
be gauged well with the help of a recent global atlas to the energy
density of the upper winds at different altitudes between 80 m and
12,000 m. [Xvi] Flight wind power plants can also be operated within
their maximum design maximum height in different varying
heights. As a result, the height can be changed at low wind at a
certain height. In addition, can be used from one place to wind
energy from different heights, so that the usable as opposed to
conventional wind turbines wind energy per unit area
multiplied. This could be achieved on a small floor space
significantly higher amounts of energy, land use, and the impact on the
landscape would thus be reduced. The higher the wind speed at
higher altitudes also means less downtime of the wind turbines. To
produce conventional wind turbines by wind, depending on location, on
average, only 30-40% of their rated power. [Xvii] In contrast,
projected to high altitude wind turbines of up to 80% capacity
utilization. [Xviii] This effect would improve the consistency of
wind energy and thus mitigate a significant problem of wind
energy. The associated rise to the Provision of alternative power
sources, mostly from fossil fuels such as coal or gas would be
eased. In addition, the electricity price drops due to the higher
utilization of power plants. Due to the higher average wind speeds
and lower depending on the soil conditions and the strength of the
surface winds altitude wind power plants can also unsuitable for
conventional wind turbines locations, such as in low-wind inland
operate. Locations for wind power plants could thus depend on the
power consumption in the region and less by the wind speed on the
ground. As a result, the space required for the conversion of wind
energy on energy consumption for network expansion itself could
decrease. This requires about Germany in the transportation of
wind power from the wind strong producing areas in the north to the
consumption centers in the central and southern
Germany. Assessments by various assume that the producer price of
less than 1 Euro cent per kWh of electricity could be realistic up to 2
cents per kWh of electricity. [Xix] This means that flight wind power
plants could produce up to 10-20 times cheaper electricity than
conventional wind turbines. [xx] Should this view be correct, flight
wind power plants would not only be by far the cheapest source of
renewable energy, but also at least as favorable as fossil fuel power
plants, even without taking into account externalities such as CO2
pollution. [xxi] For the use of wind energy is the Winds of fundamental
importance. The usable energy increases not only linearly with
wind speed, but decreases with the cube of the wind speed. [Xv]
This means that if you double the wind speed, the energy contained in
the wind
Design principles of flight wind power plants [ Edit ]
To
achieve the winds aloft the Airborne wind turbine is not fixed, unlike
conventional wind turbine on a tower or mast. Buildings with a
height of several hundred meters or even kilometers are not or not
created with reasonable effort. Flight wind power plants based on
the fact that the wing is only held by a rope or cable. The
Airborne wind turbine flying on this cable because it is lighter than
air or held by the buoyancy of the wind in the air. This is a task
to distinguish between the balloon-like, filled with light gases and
thus suspended without dynamic lift flight wind power plants, which are
lighter than air. An example of such an approach is the flight
wind turbine from Magenn. This is a rotatably mounted about the
longitudinal axis of elongated balloon like an anemometer or a
Savoniusrotor rotates thanks mounted on the longitudinal side curved
slats around the longitudinal axis and so drives a generator. The
alternative is flight wind power plants, which are heavier than
air. These convert a portion of the wind energy into dynamic
buoyancy that keeps the Airborne wind turbine like a kite or kite
sailing in the air. These systems provide a considerably higher
demands on the control as a control error usually results in a
crash. The proposed systems further differ in whether the
electricity in the air takes place and is then transmitted via cable or
wirelessly to the ground or if the power is mechanically transmitted to
the generator at the ground station. Other types derive the
kinetic energy about on ropes or chains to the floor. The
generator produces electricity then on the ground. Furthermore, a
distinction between power plants, flying or hovering stationary over a
place, as well as between power plants, thereby increasing the energy
efficiency, they quickly crosswind fly (Cross-Wind Power), such as in a
circular motion or in the form of a. 8 These maneuvers, which are also
used in kitesurfing, increase the swept from the wing surface, the
relative wind speed on the wing and usable by the power plant wind
energy. The principle behind it can be explained well by
comparison with conventional wind turbines. In these, the tips of
the wind turbine produce a large part of the total energy of a wind
turbine. This is because these peaks extremely fast spin in a
circle, and thus sweep over a large area. The wind is decelerated
to the total swept area and not only on the circle cutout on which the
wing is straight. Designers 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.
Structural differences of Flight wind power plants to conventional wind power plants [ Edit ]
Design and materials [ Edit ]
The
flying part of a flight wind power plant to be built easily. To
make this addition to the choice of textile and flexible materials are
to choose designs that strain the material in its most advantageous
way. This means that as only tensile and compressive forces but
hardly gravitational forces should act on the individual components as
possible. In conventional wind turbines, but just these lateral
forces prevail, so that the towers, blades, etc. have to be extremely
stable dimensioned to withstand these lateral forces can.Thus, the
required mass of these components increased many times
over. Gravitational forces may anchoring ropes, as is the case
with kites, be almost completely avoided.Increase bracing However, the
air resistance significantly. As far as fast flight, the power
output is to be increased, however, you have to keep 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. [Xxii] However, even with
commercial Surfkites that are not aerodynamically optimal remarkable
achievements of 30 [xxiii] and 40 kw [xxiv] calculated or have been
achieved , Dyneema® is mostly used [xxv] for the ropes, with new
materials such as nanotubes, could dramatically increase the
performance and capabilities of flight wind power plants.
Command and control [ Edit ]
The
autonomous control of the flight wind power plants and the fact that
they fly in contrast to conventional wind power plants anywhere in the
room, represents a key challenge in the development of flight wind
power plants. [Xxvi] Previous 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, direction of movement, rope tension, vibration, 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 greatest
possible energy. In this case, make sudden and unexpected changes
in wind speed and direction is a particular problem. Challenges also
exist in the takeoff and landing phase, possibly an entirely different
aircraft 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 on airport wind
power plants. In recent years, a variety of progress has been made in
this field, however, so that appropriate sensors are now available at
low cost.Meanwhile, mobile phones are equipped as standard GPS sensors
or even position sensors (such as iPhone and Wii controller)
itself. The actual flight control is performed either as a plane
through various attached to the Airborne wind turbine (elevator,
rudder, aileron) Rowing, or according to the control with kites and
kite 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. As an alternative, in itself, to
bring together the steering parts in a steering module under the
wing. The further connection to the ground station would then take
place over a single cable. The steering module would then have to
perform the steering movements but have a source of energy. This
takes about using batteries in a built-in the cable power cable [xxvii]
or by small wind turbines on the wing, which generate the operating
current, done.
Electricity generation [ Edit ]
Basically, the power generation can be carried out in the air or at the ground station.
Electricity in the air [ Edit ]
To
generate electricity in the air basically the potentially serious power
generators shall 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 is also conceivable that transmission
without power line would be approximately over microwave etc.
conceivable power generation would be flying in the air by wind
turbines. The lack of anchorage can be replaced by two
counter-rotating wind turbines on a shaft or for example by a plurality
of smaller wind turbines that are held by a frame. The latter
approach is taken by Skywindpower whose prototype has four
helicopter-like rotors. The electricity in the air can
alternatively be carried out by a small, vertically mounted like an
airplane wing propeller connected to the generator. The wing while
flying fast circular movements and is decelerated by the drive of
propeller and generator. This concept corresponds largely to the
implementation of autonomous leaf tips of a conventional wind
turbine. Only the braking 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. An
advantage of most of these designs is that the generator during a lull,
and for launching and landings can be used as a motor. The
proposal of Makani and Joby Energy looks like before takeoff and
landing in a helicopter, with energy being expended. With this
option, the start and the safe landing during a lull is self-sufficient
in these possible variations. In addition, an increased
maneuverability increases in some variants by the possibility of
controlling various motors similar to a mehrrotorigen
helicopter. In the air, the described circular movement is then
performed to generate electricity. Through the power line to the
ground also the energy supply of the sensors and control of the wing is
secured.
Power generation at the bottom [ Edit ]
When
electricity is generated at the bottom of the generator is in the
ground station. The energy is mechanically, usually by means of
cables, transmitted from the airfoil to the ground station. The
most favored variant is the so-called Jo-Jo configuration. In this
case, the lift generated by the wing is used to pull the
tether. The tether is released slowly and thereby drives the base
station via a cable drum a generator. Once the end position is
reached, the rope under expenditure of energy must be
recovered. In this case, the wing is found to have a very low wind
resistance and minimal time and energy required for recovering the
rope. Then the cycle starts all over again. Other
alternatives provide that the kinetic energy is transferred by a
rapidly rotating tether, which thus serves as a wave, to the
ground. The laddermill [xxviii] referred to the 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 made so that they generate lift and
pull one end of the rope to the top, the other wings are neutral set so
that they produce the least possible resistance in the fall. At
the ground station said apparatus, 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
are less expensive. The ground station with the generator of a
yo-yo configuration could be used for new technologies in
Tragflügelbau. Possibly would also be possible, depending on the
wind situation hydrofoil to use with different sizes or aerodynamic
properties or to drive the generator with several wings at low
wind. The disadvantages are seen in the need for the supporting
surface energy supply as well as the inability of the autonomous
takeoff and landing by helicopter principle.
Challenges in the development and operation of aircraft wind power plants [ Edit ]
In
addition to the mentioned 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 [ Edit ]
Flight
wind power plants can be operated beyond the airspace of 100m height
addition, for there is competition and risk of collision with
aircraft. It is primarily a competition with the private flying
for the use of up to 1000 m. To ensure the security of private
flying should be set to the location of wind farms flight fly zones to
ensure, as they now exist already on nuclear power plants and other
built-up areas. In the relatively low service life of the
installed Skysail drives a near-collision has taken place with a
helicopter. [Xxix]
Lightning and extreme weather conditions [ Edit ]
The
long tethers are excellent conductors, is likely to result in increased
thunderstorm with lightning strikes. In this case, however, there
appears to be sufficient to allow appropriate insulation of the wing
and the ground station against lightning. Furthermore, flight wind
power plants can be landed in appropriate weather conditions. This
raises the question remains whether in cold weather the wing icing is a
major problem. Furthermore, the question arises how quickly the
materials as well as the cables used in continuous operation wear out
and must be replaced.
Crashes [ Edit ]
It
is difficult to calculate due to the complex control of the flight of
wind power plants as air, at least in the test phase with increased
crash. Even with sophisticated systems, crashes can probably not
be excluded with certainty. Therefore Flight wind power plants
should only come into question in such locations where a risk to humans
is excluded. [Xxx]
Legal and operating license [ Edit ]
Exist
for the construction and operation of aircraft wind power plants in
2010 for Germany as yet no specific regulations. Construction
(planungs) legal and aviation law permits should be obtained only with
considerable effort by individual decisions. Flight wind power
plants should, however, not unlike conventional wind power plants, the
feed-in tariff according to the Renewable Energy Sources Act (EEG) was
obtained.
Interesting links: [ Edit ]
- www.Makani.com
- Congress flight Wind Power Plants 2010 (
