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The above radio controlled kite was flown on Aug. 29, 2007 in northern Europe as part of a "ladder-mill" set of such kites, creating 10.5 kilowatts of electricity.

The Laddermill is a high altitude wind power design which consists of a series of wings or kites all connected to the ground via cable, forming a huge rotating loop.

After extensive 3D modelling, the system was successfully tested on Aug. 29, 2007.

Once commercialized, the system is expected to generate electricity at around 5 cents per kilowat-hour, with costs spread over 4-5 years; which is competative with the cheaper conventional utility scale electricity costs.

"At the moment we are the only developers who have managed to succeeed in this concept, although other groups are also testing it in Italy and Australia" -- Dr Wubbo Ockels (Aug. 29, 2007) [1]

## How it Works

Quoting from http://www.ockels.nl/Introduction.htm

The Laddermill consists of a series of wings or kites all connected to a cable that forms a huge loop. Like the wings of an aeroplane will the wind cause an upward lift force to the wings. By changing the attitude of the wing (angle of attack with respect to the wind) can the lift force be made larger or smaller.

The wings on one side of the cable loop are all placed such that they produce the maximum lift force, while the wings on the other side of the loop will give a much smaller lift that in fact is just sufficient to support their own weight and the weight of the cable.

The result is a large difference in force between the two ends at the ground. When the cable loop is guided around a wheel on the ground the force difference will drive the wheel. By connecting the wheel to a generator electricity will be produced.

The wind energy aloft has thus been transferred to electricity on the ground.

## Cost

The cost calculations include the cable and wing constructions as well as the ground station mechanisms, power conversion and storage. These calculations lead to an expected installation cost of FL 1000.- or 400 US\$ per kilowatt. A 10 megawatt Laddermill system would thus cost 8 million guilders and would provide an average of 3.5 megawatt electrical power. This leads to 5 cent/kWh when amortising the investment over 4-5 years. [2]

## Profiles

### Company: Drachen Foundation

This method is being considered at Delft University in the Netherlands.

### Inventor: Wubbo Ockels

Invented by Dutch astronaut-scientist Dr. Wubbo Ockels.

# Coverage

## In the News

• Scientists look high in the sky for power - By lofting generators into the upper atmosphere, scientists theorize they could capture the power of the jet stream and transmit the electricity along cables back to Earth. Dozens of researchers around the world believe huge kite-like wind-power generators could be the solution, potentially meeting the world's entire electrical needs. (San Fransico Chronicle; May 7, 2007)
• Harvesting Energy in the Sky - Article addresses airborne -- up to 10km in the sky -- wind farms intended to harvest the immense supply of energy in the jet stream. San Diego-based Sky WindPower believes they can not only make this work, but do so profitably. Several other ideas discussed for high-flying wind farming including a Dutch proposal to use pairs of kites to drive a generator. (The Economist; Apr. 3, 2007) (See Slashdot discussion)
• Wind Power "Laddermills": High Altitude Kites to Replace Turbines - Concept of 5-mile-into-the-sky cable with chain of controllable wing-like kites attached to a looped cable, generating 100 MW. Developers at Delft Technical University in the Netherlands hope to build a working model in the next four years. (Alt Eng News; Dec. 19, 2004)

## Other Coverage

• Interview Wubbo Ockels - Prof dr Wubbo Ockels is de man die Nederland op de kaart zette van de ... om met behulp van wind en vleugels grote hoeveelheden energie op te wekken. ... (Ecoboot.nl)

# Contact

Website assigned to:

W. J. Ockels
Wubbo Ockels BV
Boekenroodeweg 45
2111HK AERDENHOUT
Netherlands

Wubbo Ockels email: wubbo.ockels {at} worldonline.nl

Dave Lang email: ddlang {at} cypressmail.net.

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