If we take a look at the weight of renewable energies in energy generation (for example, in Europe), we are going to find that some, such as wind and solar, are the ones that call the shots while others have a testimonial contribution: this is the case of wave drivebetter known as wave energy. Yes, the resource is there to take advantage of (and in some places like the Cantabrian coast to give and give away), but it is one thing to surf and another to obtain energy.
Because the waves that reach the buoy this morning have nothing to do with those that do so in the afternoon: another height, another rhythm, another direction… it is part of the charm of surfing but it is also a nightmare to get electricity. The wave works, but it is unpredictable and not constant, which reduces efficiency. So Takahito Iida, a researcher at the Department of Naval Architecture and Ocean Engineering at Osaka University, has come up with a solution to that problem that he has published in the Journal of Fluid Mechanics: a rotating steering wheel.
The invention. The device is called GWEC (Gyroscopic Wave Energy Converter). The idea in essence is a rotating flywheel inside a floating buoy that allows you to extract maximum energy from the waves regardless of their frequency.
It does not follow the movement of the waves, but rather converts it into a perpendicular rotation that drives a generator. The trick is to adjust the rotation speed of the steering wheel in real time: this way the system adapts to the sea instead of waiting for the sea to adapt to the ideal conditions of the device.
Why is it important. Because wave energy continues to be the eternal promise of energy and the oceans They cover 71% of the Earthaccumulating a large amount of energy. All previous systems failed in something: they are optimized for the resonant frequency, a single and specific one. At that moment it reaches its maximum efficiency of 50%, the maximum that physics allows. Iida’s GWEC is capable of maintaining it across the entire frequency band.
Context. The time to publish the paper could not be better: the price of oil exceeds 100 dollars the barrel and Japan 95% matters its own in the Middle East, so the search for alternatives is urgent.
The basic idea is not new, the novelty is knowing how to control it so that it performs at its maximum regardless of the sea. In fact, the concept was patented in 1981 by engineers Laithwaite and Salter and prototypes have been tested since then in Japan, Spain and Italy. What no one had done until now is a complete theoretical analysis that explains how to “tune” the system in any wave condition.
How do you do it. Iida develops for the first time the complete equations of the entire system, including the waves, the platform and the gyroscope, and also identifies the optimal control parameters (the stiffness of the generator, its damping and the speed of the flywheel). Likewise, it shows that with the system well adjusted, the system can reach the theoretical physical limit of energy absorption: exactly half of the energy carried by each wave.
Why half? A wave arriving at a symmetrical body is divided equally between symmetrical and asymmetrical components. A device with only one type of movement can only capture the asymmetric component. Be careful, it’s not that more can’t be absorbed, but it would be necessary to have asymmetric geometries (such as the salter duck) or more complex systems.
Yes, but. Iida has tested his device and equations on a laboratory scale, where practice has been adjusted to theory, but it is still a device under controlled conditions. The declared next step is tests with a physical model in the wave channel of Osaka University
Additionally, there are other limitations such as it only works with small waves (if the waves grow, the physics is no longer linear), which reduces its efficiency. The author is clear: the valid range of the amplitude is too small for real use. Similarly, mechanical losses have not yet been quantified.
In Xataka | Something is happening in the oceans for which we have no convincing explanation: the waves are disappearing
In Xataka | When an earthquake hit Kamchatka, tens of thousands of people in Japan did the same: climb onto the roofs
Cover | Jeremy Bishop and David Edelstein
GIPHY App Key not set. Please check settings