Ampyx Power is to design a high-strength rope or ‘tether’ for its breakthrough Airborne Wind Energy System (AWES), a second-generation wind energy technology using a tethered aircraft. In partnership with DSM a project has now started to demonstrate a tether that is sized to generate up to 2 MW, the first time a tether for Airborne Wind Energy will be developed and tested at a multi-megawatt scale. The tether will be made from Dyneema®, world’s strongest fiber.

Press release DSM

Ampyx Power’s initial commercial AWES will ‘repower’ the first generation of offshore wind farms. Constructed in the early 2000s and designed for onshore rather than offshore use, these turbines will reach the end of their lives between 2020 and 2025. The supporting infrastructure, however, will not. The AWES can be applied to extend the life of these wind farms by retaining the foundations and infrastructure and adding a platform to launch and land a tethered aircraft. Once launched, the efficient kites will fly at a height of 200-450 meters – beyond the reach of current wind turbines – where winds are stronger and more consistent. In the further future, after repowering first generation wind farms, the technology can be applied offshore on floating platforms and in remoted areas on land. With this technology new areas can be unlocked for cost-effective harvesting of wind energy.

Key to the design is a tether that connects the aircraft to a generator on the ground. As the aircraft moves, it pulls the tether from a drum, which drives the generator. Once the tether has been fully reeled out – about 750 meters – the kite automatically descends, the tether reels in and the kite then climbs again and repeats the process.

All this means that the tether needs to be durable enough to handle high forces 24-7.  Together with Ampyx Power DSM defined the needs to design a tether that is safe, durable, strong and keeps maintenance and replacement costs to a minimum.

In an AWE system, the tether needs to be thin, light and very strong. Thin, to minimize aerodynamic drag and so maximize energy output and operational efficiency. Durable, because it will have to wind and unwind around the sheaves of the generator up to a million times a year. Light, because it will have to be replaced regularly, often in a tough operating environment. Dyneema® fiber checks all the boxes. It is a very durable and low friction material, extremely light, and its high tensile strength means that compared with other materials, you can use smaller-diameter ropes for the same tether load.

TKI Wind op Zee (Top consortium for Knowledge and Innovation Offshore Wind), part of the Top Sector Energy, has granted subsidy for the tether project. It involves both developing the mathematical models needed to design and test optimized AWES tethers and building a test setup for scaling up tethers for megawatt-scale application. The tether will be designed, built and tested in a setup that mimics a realistic operational environment.

Until the commercial 2 MW release, Ampyx Power is working on a smaller scale prototype AWES, using a different type of Dyneema tether with less demanding requirements. The prototype will fly at a test site in Ireland next year. With this fully automatic prototype Ampyx Power will test the technologies, architecture, organization, and processes for the future commercial product.