Our Journey

After having observed the limitations of existing tidal technologies and in-depth research in the field, the first conceptual idea of an underwater kite that could harvest energy from tidal currents was formulated by Youri Wentzel in 2014.

The next goal was obtaining experimental proof for the TidalKite technology concept. In order to achieve this, SeaQurrent contacted the University of Groningen (RUG) in the summer of 2015, which represented the beginning of a fruitful partnership. The RUG was contracted to validate the technological feasibility of the TidalKite Power Plant. The RUG was given two main tasks: the first one was to design a predictive computer model that could give indications of the energy yields of the system, and to analyse the sensitivity of the performance and configuration of individual components. The performance of many different wing profiles was modelled and the effect on performance of different wing properties was outlined. The most promising wing profiles were identified and then tested experimentally in the RUG flow channel, to investigate which one was the best performing. Not only was the individual performance of the wings analysed, but also the effect of placing multiple wings in tandem was researched. Based on wing profile modelling and on the results obtained from the flow channel performance, the results confirmed that the in-tandem configuration is optimal for maximum extraction of energy from the water stream. SeaQurrent was able to prove that the TidalKite can generate lift and ‘3D-harness’ an entire water column. Further, the literature supported SeaQurrent’s claims regarding energy efficiency, the wings’ in-tandem configuration and power production by moving a system across a water flow. Together with the RUG, SeaQurrent created an energy production model to validate predictions regarding wing performance in laboratory experiments. At the same time, the small testing environment at the RUG bore certain limitations: not all components could be tested, and the working principles of the technology could not yet be validated. This was to be investigated in the next TRL phase.

In parallel, SeaQurrent started exploring and developing which control methods were available to manage and operate the wings of the TidalKite.

After having obtained experimental proof in TRL 3, SeaQurrent focused on validating a prototype of the technology in a laboratory environment. SeaQurrent designed, built and successfully tested the prototype in a shallow flow basin at the Maritime Research Institute Netherlands (MARIN) in Wageningen (NL), one of the largest nautical research institutes in the world. These tests were again carried out in cooperation with the University of Groningen.

Prof dr Eize Stamhuis of the University of Groningen: “The field test of the prototype at Marin shows that the prototype already generates large forces at low velocities, which are in line with the predictions of the theoretical model”.

The prototype could successfully be steered from one side of the basin to the other, realising first flight. SeaQurrent also demonstrated that the in-tandem configuration of the wings is very efficient to increase the total lift force. The generated lift force was as expected. Due to the limitations of both the test setup and the available shallow basin, the rotation of the TidalKite could not be tested.

In parallel, SeaQurrent developed the visualisation and control environment (software), as well as a control hardware layout, which represented the foundation of the autonomous control system of the first prototype of the TidalKite to be tested at sea.
Alongside the TidalKite development and prototype tests, SeaQurrent also began to work on designing the Power Take- Off (PTO) system in 2017. While the basic principles of the PTO systems are already well established, SeaQurrent uses existing available technology in a configuration completely tailored to the TidalKite; combining existing components to design a reliable, highly efficient, minimum-risk PTO. Quoceant, a Scottish maritime engineering consultancy company with ample experience in PTO system building, was also involved to review the design. SeaQurrent successfully tested the newly constructed PTO as a standalone system, in order to be tested in combination with the TidalKite at sea. The results showed that during normal production the PTO has an energy conversion efficiency of 80%, which is comparable to the efficiency of other existing PTO configurations.

In conclusion, TRL 4 resulted in very satisfactory laboratory results at the MARIN test facilities, the interdisciplinary collaboration of multiple technical teams and the design of the kite and PTO system.

TRL 5 consisted of two separate testing phases. The main goal of the first testing phase was to design, construct and do submerged tests with a functioning kite, in order to reduce the uncertainties regarding individual components and system configuration. With the obtained experience and test results, SeaQurrent then embarked on a second testing phase, with the aim to fulfil the following TRL5 goals, with an improved system.

1. The development and construction of a robust and efficient scale model of the TidalKite
2. The autonomous operation and the underwater monitoring of the kite
3. Monitor and minimising environmental impact of the TidalKite in a flow channel
4. Testing the new TidalKite scale model in combination with the newly constructed PTO system.

SeaQurrent prepared and arranged all the required permits and consents, to be able to perform these sea tests in 2018/2019. The first testing period started in August 2018 with the testing of a first scale model of the TidalKite (2018 TidalKite). A year later, SeaQurrent began testing the second TidalKite scale model (2019 TidalKite), finishing in November 2019. For clarity purposes, the testing operations for 2018 and 2019 TidalKite are described in two separate sections.

SeaQurrent received permission to set up the 2018 TidalKite on a barge in the Wadden Sea close to the Afsluitdijk. As previously outlined, SeaQurrent wanted to create a working system underwater, therefore carried out electronic tests, sensor tests, watertight box tests, wing movement tests and buoyancy tests, while also aiming to manoeuvre the kite under water in anticipation of fully autonomous flight.

As for the achievements, SeaQurrent was able to calibrate the buoyancy of the TidalKite, to monitor, program and control the kite from the control-room. Further, both controllers and electronics worked successfully underwater. Tests also validated the working principle of most individual components.

In addition to the testing of the TidalKite, additional valuable insights were gained in durability, performance and the reliability of components and costs. Insights in the required testing setup, testing conditions, handling and limitations.

In August 2019, SeaQurrent embarked on a new testing period with the improved 2019 TidalKite.

The results of the tests are positive. Compared to the 2018 TidalKite, the 2019 model was a more sophisticated system. The 2019 TidalKite was a robust system that could successfully endure the long-term and intense testing programs. The 2019 TidalKite could be optimally controlled and monitored underwater. Furthermore, the stages of the flight trajectory could be completed successfully. Also, we where able to successfully rotate the TidalKite with the help of the PTO by retracting the main hydraulic cylinder during rotation.

With regards to the minimising environmental impact, SeaQurrent carried out several analyses and tests to assess the effects. Acoustic measurements were carried out with a hydrophone, where it was found that the underwater sound produced by the 2019 TidalKite is negligible. Calculations were also realised to investigate fish safety: the NEN8775 norm, carried out by the Royal NEN Independent Institute for norms and standardisations, was applied to the TidalKite and the correctness hereof was confirmed by the NEN8775 core team. The results showed minimal fish mortality. Ecologist observations have confirmed that marine mammals and birds are not disturbed by the TidalKite presence. Lastly, the University of Groningen carried out tests in their flow channels and performed CFD modelling1 to assess whether the wake of the TidalKite, while flying close to the seabed, affects the soil and disturbs the contained benthos. After accurate calculations and comparisons with the existing literature, it was established that no disturbance is caused by the presence of the TidalKite, if the TidalKite stays 1 meter from the seabed.

While results were very satisfactory, the testing setup presented also some valuable learnings and test plan adaptations. The main restriction was the limited water depth on site. Due to the shallow water, manoeuvres had to be performed very accurately (the margin of error was only 1m). If the kite got too close to the bottom or surface – outside the defined safe operating limits – activation of the safety system would trigger the recovery mode and the kite to resurface. As such, it was not possible to already demonstrate the full flight pattern continuously, but it was possible to test the individual flight stages, such as the back and forth movement, and the rotation. Key learning is that a deeper test location is needed.

In addition, handling the tether turned out to be challenging. During the testing period, the primary hydrodynamic tether design appeared to be not robust enough for repeated handling during everyday testing; requiring the kite and the tether to be taken in and out the water daily. This was caused by the fact that its hydrodynamic shell (fairing) was too vulnerable to handle. Thus, this hydrodynamic shell had to be removed to be able to continue testing. Due to the necessary changes, the tether-drag increased substantially. Key learning is to design for extensive handling during test periods first and add hydrodynamic optimisation later.

This, combined with the fact that the location was too shallow for continuous flight, rendered it no longer feasible to test the full functionality of the PTO and TidalKite combination on this location. Attempts to test the system-integration in deeper waters in the North Sea were hindered due to the long swell, causing the barge to become unstable and handling of the system unsafe. Key learnings are translated in the optimized operational handling procedure.

We are developing a technology demonstrator with full scale components consisting of kite, tether, PTO and mooring, that will be assembled in our production facility in Drachten. In 2022 the demonstrator will be deployed at a grid connected test site in the Waddenzee, with all permits (in place) and a power cable from the test site to the electricity grid on the island of Ameland.

EIC accelerator project

Full scale model (500kW)

Commercial pilot

Market introduction

10MW commercial project

Continued R&D roadmap