What happens when the wind turns to still conditions? Do the kites fall down?

No. The kites can be maintained at altitudes in still wind conditions. Studies have shown that a start-up speed of X-Wind systems of 2 to 3 m/s proves positive approx. 90% of the time from various data collection points. This means that 10% of the time wind speed is lower. During still periods of predominantly short duration the energy generating system changes to an energy using system. In this case the generator act as motors to pull grounded vehicles. These are then propelled at a speed of at least 2m/s to maneuver the kite in the sky. It is literally like a child running to keep his kite in the air. Should a longer period of still conditions be anticipated the system is shut down and the flight vehicles are stored on the ground. Ideally these operational interludes are utilized for service and maintenance purposes.

Will kites be taken down and stored in time in case of an anticipated storm? What happens in unforeseen strong wind conditions?

The X-Wind-kites are started just like a kite you would raise at home: run for the first few meters to propel the kite in the air to then continue rising on its own. Parallel to the actual rail system there is an additional raising and landing path where the grounded vehicles could speed up at a rate of 2-3m/s to raise flight vehicles. 

How is energy generated by the main system?

There are several means to extract energy from the system.
Here too X-Wind systems has selected proven technology of cable car systems: the grounded vehicles are connected via a steel cable laid vertically/perpendicularly to the rolling stock. As in cable car and chair lift systems energy is transmitted through the rolling stock to bring the system in motion. In the same reverse manner the energy generated from the kites is transmitted via the tow lines into the NTS grounded system. Such technologies have been in use for decades.
In a next step we will be able to waive the ground cable by using drive units of modern energy supplying locomotive engines (still under development) but more efficient.

X-Wind Power production

When I drive along the highway I see most wind turbines standing still. Do NTS systems also only periodically generating energy?

With increasing altitude wind speed not only increases but also becomes more stable. From studies we know that a start-up speed on 2m/s persists at most locations for up to 90% of the time. This means that kites can be kept in the air for up to 330 days per year. Energy production by X-Wind systems is therefore many times more continual and predictable than existing wind energy systems. With X-Wind systems a different problem arises when continually generating energy: the system also generates energy during times of low demand for example after midnight. This energy requires storage and disposal during periods of higher demand. aap is investigating a storage system using hydrogen technology.

PICD000019 2011 06 06 Frequency scale of windspeed NTS made

What are the aviation authorities saying? Do the systems inhibit air traffic?

With operational locations in Germany aap has consciously chosen a country with the highest safety standards and requirements for approval processes of flight vehicles. As a first step the former NTS has engaged the Kleiner/Düsseldorf Law Firm, one of the most experienced firms in this field, to compile an aviation report and to check the general potential of gaining approval. Initial requirement criteria for approval were collected in consultation with the respective authorities and institutions, namely the Ministry for Transport, the Aviation Authority, Flight Safety Authority and other regional aviation departments.
A protected zone is required for the operation of X-Wind systems. A requirement to clearly mark and label tow-lines and kites seems logical. The approval for the operation of the system is made dependent upon the location of the plant to be individually assessed. Applications for approval have not been lodged to date as the final choice of location for the first operational X-Wind system has not been made. The general responses from various authorities and institutes are positive. Domestic air traffic is not inhibited at an operational altitude of 500m although safe distance to airports and starting /landing paths certainly require consideration. The establishment of a flight control zone will serve to safeguard private air travel and keep minimum sight distance to for example helicopters (800m).

Would it not be more suitable to operate NTS systems off-shore?

A major advantage of X-Wind systems is the proximity to the consumer. German prime industries consuming large amounts of energy are located in the south of the country distant to the coast. X-Wind systems can be built in close proximity to industrial areas to generate co2-free energy as here too the wind conditions at 500m altitude are significantly more stable than on the ground. This not only saves substantial transport and investment costs of an off-shore system but also reduces service and maintenance costs of an on-shore system to a fraction of those of an off-shore variation.

Why is the expected efficiency of the system up to three times higher than of a conventional windmill?

The efficiency of X-Wind systems is estimated to be much higher than that of existing on-shore windmills because much stronger and more stable wind conditions are expected at an altitude of 500m and because a start-up speed of 2m/s is much lower than current systems require.

Windspeeds and frequency

What risks of accident conditions are possible between kites in a system operating 24 kites?

lying eight NTS wind powerThe kites are operated dynamically meaning they move in different directions. Even when wind conditions come from a predominant direction a change of maneuver of individual kites ispossible according to vertical or local conditions. This is why kites are kept at a safe distance of 200-400m to avoid immediate collision and to get them under control on an elliptic system. The steering software of the whole systems is responsible to avoid accidents between kites.
In the opposite wind direction the energy kite is steered into idle position and the power unit move (pulls) it around the corner by using electricity.

kites on an X-Wind

Why does the grounded system have an elliptic shape and not a circle?

Generally the kites generate propulsion at 50° to the wind. In a 360° circuit there are therefore 260° with driving force meaning energy generation and a remaining 100° where kites are exposed to winds with no drag. The ratio between driving force and head wind is 2.6:1. As prevalent wind conditions exist at most locations this ratio can be increased enormously by creating an elliptic circuit instead of a circular system. The circuit is laid out diagonally to the main wind direction so that there is only one curve in the whole track system confronting head wind conditions. The longer and thereby narrower the track is the higher the ratio is between the driving force and head wind routes. For one of the former NTS studies the local conditions determined a triangular circuit for maximum energy generation yet an elliptic system remains most efficient.

NTS X-Wind generator top view

When flight vehicles travel on an elliptic circuit does it not eventually come to a halt in head wind?

This is what the former NTS patent claims focus upon: When flight vehicles get into a sphere where propulsion is not possible they are maneuvered in such a way that their resistaWind window of kitesnce to the wind is as low as possible. This can be achieved for example by guiding kites to lower altitudes where head wind conditions are considerably lower. In such situations the kites are made “non-resistant”. When the kite is completely vertical to the ground it has minimal contact surface to the wind. It requires minimal auxiliary force to maintain a kite in this position even of very large size. Only once the kite is guided beyond a few degrees to its “12.00 position” it unfolds its maximum driving force. So when a kite comes into head wind its resistance is greatly reduced and guided by other vehicles to which it is connected to a position in which it can capture propulsion again to generate energy. Generally there are 2 kites in head wind position in a 24 kite system where it requires minimal energy taken from the remaining 22 kites to drag the 2 non-performing vehicles back to operating status.


Why a circuit system and not a straight line for a kite to move up and down?

On a straight line only a single flight vehicle can maneuver up and down which requires bringing to a standstill and diverting back in the opposite direction using energy to get the kite back into its energy generating cycle. In order to generate energy from such a system the rail line would need to be very long and that for one vehicle only. The X-Wind solution which guides flight vehicles in circular motion is significantly more efficient: several flight vehicles can travel along a shorter distance.

Why is the rail system raised and not connected to the ground?

The rail system is mounted on 6 m foundations to exploit three advantages:

  1. Ultimate use of inner land area for agricultural use: vehicles can cross the perimeter below.
  2. Safety against vandalism
  3. Better starting conditions: as wind conditions increase with height the kites have a definite necessary height to start faster.

But X-Wind systems are also mountable on ground. From the cost perspective much cheaper.

How much area does the system require and can the land be used for auxiliary purposes?

An X-Wind system was simulated for the BMW plant at Leipzig with a capacity of 118 GW per year. In this manner this production plant alone saves 47000t CO2 emissions per year. Located close to the plant using available materials and conditions the system would require 24 flight objects. For this simulation a safe distance of 200 to 400m between flight objects is maintained requiring a total track length of 4800 to 9600m. Such a system would be approx. 2000 to 4000m long and 800m wide. In comparison the Leipzig plant requires 30 modern 2MW windmills to generate 118GW per year (each 2MW system generates approx. 4GW per year). As such conventional systems also require safe distance between their units the area requirements for a conventional 118GW/year wind-farm would be of similar size to a respective X-Wind system. At this stage aap expects the land is appropriate for continuing agricultural use as the actual area used for energy generating purposes is reduced to the foundations only and thereby tiny compared to other land uses such as agriculture.

Area needed for different types of energy generation

How many households can be serviced by an X-Wind system?

The per capita consumption of energy in Germany is approx. 4000kW per year. An X-Wind system generating 120 GW per year can service 30.000 households. The costs of such a system are estimated at less than 35m Euro.

Power output of X-wind kite power plant

Are the grounded rolling units connected?

For our next generation power units no, but they are virtual connected by distance measuring systems. This system guarantees a safe distance between the ground units and the flight objects.

If you have more questions, feel free to contact us.