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Deep thinking

8th November 2018


The subsea kite uses the force of the stream flow to 'fly' across the current
Deep sea trial of Minesto's DG500 unit
Scale model prototype testing

Louise Smyth meets the CEO of an innovative tech firm that’s bringing a novel marine energy solution to market

There’s a great deal of crossover between various engineering disciplines and it’s always interesting to see an idea that emerged from one industry be tweaked and adopted by another. It’s often the aerospace sector we see ‘borrowing’ technology that’s been successful elsewhere, usually becoming a later adopter due to its stringent safety requirements. However, in the case of Deep Green technology, the reverse scenario has occurred: a concept dreamed up at an aerospace company has been developed into an impressive marine energy technology.

Dr Martin Edlund, CEO of the firm created as a spin-off from the original idea, explains how the technology came to life. “It was invented by an engineer with the aerospace company Saab, within the scope of a wind turbine study where vertical-axis turbine concepts were explored,” he begins. “The idea was then taken to Chalmers University of Technology in Gothenburg to evaluate the technical and commercial viability. In that environment the company Minesto was founded and the technology has been developed since then, with several generations of prototypes tested first in basins and since 2011, in the ocean.”  

So how does the Deep Green solution actually work? “The technology is a unique marine energy converter, a subsea kite that targets the global low-flow tidal stream and ocean current resource,” explains Edlund. “It consists of a wing that is tethered to the seabed and that carries a turbine underneath. Our subsea kite technology converts kinetic energy to electricity by way of a unique principle similar to flying a stunt kite in the wind. The Minesto kite uses the lift force of the stream flow to “fly” across the underwater current, pushing the turbine through the water at a speed several times the actual stream flow. Electricity is produced in the onboard generator and transmitted through the tether to seabed cables.”

BLEND OF UNIQUE AND STANDARD COMPONENTS

The main components of the power plant itself are the wing and, attached underneath, the nacelle housing control and electrical system, generator and turbine. Rudders mounted at the end of the nacelle enable the device to move in its pre-determined trajectory, and struts and a top joint connect the wing with the tether. Edlund says that, “The tether then connects to a bottom joint that is on top of the seabed foundation – in our current installation in Wales, a gravity-based concrete structure. The tether is a unique feature and is specific to the Deep Green system, however it is made up by relatively standard components such as Dyneema fibre, electrical cables and polyurethane fairings. Each of these components are tailored to the application to match factors such as power rating, length, forces and lifetime, which is quite normal for any project.”

Edlund reveals that some of the internal components are off-the-shelf, “such as sensors, cables, inverters and connectors, whilst the external components including wing, turbine, nacelle body, struts and rudders are designed specifically for the Deep Green system.” Other components are adaptions of existing products to Minesto’s application, such as the actuators, generator and the bottom joint. For concepts such as this, the more off-the-shelf components, the better when it comes to the issue of scaling up the technology.

THE BIGGER PICTURE

Indeed, scaling up the idea has been a focus for Edlund since the start. It’s clear that the market potential is of critical importance to him. “Compared to other marine energy technologies, Minesto’s product enhances the energy conversion, making it a commercial proposition applicable to vast areas around the globe where no other known or verified technology can operate cost effectively,” he states. “Most concepts are targeting areas with very high stream flows, 2.5m/s and above. We target areas that are 2.5m/s and below, which means that we are substantially expanding the exploitable resource.”

And how far along in the commercialisation process is the technology? Edlund says: “We are engaged with demonstration of our first utility-scale device, which in the current design means a 500kW unit, off the coast of Wales. The next step of the development for that product range is to optimise it with regards to power production performance, which could mean increasing the rated power to, for example, 750kW for the next utility-scale system.”

He adds: “In parallel, we are developing a so-called Island Mode model, initially a smaller-scale system (approximately 100kW rated power) that will form a commercial product targeting off-grid applications such as island economies, aquaculture and similar.”

Minesto’s strategy for commercialisation is based on site development activities in three main geographical areas: European Atlantic coast; USA; and South East Asia. Edlund comments, “As we see it, the quickest route to market for our product in this emerging industry is for us to drive initial small-scale installations together with customers and partners, and then develop these sites into commercial electricity generating arrays.”

Ultimately, Edlund sees huge potential for his technology in the renewable energy mix. He says that, “Since Minesto addresses a part of the natural resource that no other developer is focusing on, we expand the global ocean energy potential. When you add to that the cost structure that is related to the unique competitive advantages of our technology, and the fact that we can exploit continuous ocean currents, we are talking about low-cost baseload renewable power. This means that we make ocean energy a highly relevant and urgently needed complement to the energy mix in the ongoing energy transition.”







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