Legend has it the French mathematician and engineer Pierre-Simon Girard had an intuition while watching the waves violently break against the coast: what about exploiting the mass of energy contained within them? And how to do that? Girard was first, in 1799, to patent a system for capturing wave energy. In the centuries since, hundreds of other engineers have set themselves the task of designing similar systems. All have wanted mankind to stop wasting such a promising source of energy, but only recently has the technology been developed to transform their ideas into something that could one day be of service to everyone. Today the phrase “renewable energy” brings to mind two images above all: wind turbines and endless fields of solar panels. One downside of both these “clean” energy sources is that they are not always readily available. Obviously, the sun only shines in the daytime, and even then, often hides behind the clouds. Wind is erratic by nature, and only in certain places does it blow hard enough to generate energy all the time. If these problems were not enough, the challenge of storing the energy for future use is still very much ahead of us. And as for the ocean waves? Anyone who has been to a beach will know that they break on the coast endlessly, all day and all night, all year long, which makes them an ideal source of clean energy without interruption. The overall energy density of waves is more than five times greater than that of wind and 20 times that of the sun. By converting it, we could satisfy much of the demand for electricity on the planet. Waves remain the biggest unexploited source of renewable energy in the world.
From waves to energy: a big challenge
They are predictable, unchanging, have a high energy density and can be found all over the world. Even in the gentlest Mediterranean areas (like Sicily or Sardinia) waves are available for 4,000 hours a year. But coming up with systems that can capture them is no mean feat of engineering. The first challenge is to find a suitable location, with waves that will provide enough energy but not damage the converters in violent storms. Researchers at Delft University, in Holland, have developed SWAN to get over this first hurdle. It is a piece of software that predicts the strength and direction of the waves, based on data on wind, the seabed and interactions between different waves. The system has so far been used by, among others, Nick Cartwright and Joao Nascimento, to find the most suitable places on the south-east coast of Australia, where most of the cities Down Under are to be found. “There is more than enough natural energy there in the ocean,” the two researchers explain. “The challenge is to harness and convert enough of it into power.” That challenge is a global one, in which Italy too plays its part.
Wave technologies within reach
At this year’s Maker Faire, the biggest trade fair dedicated to innovation in the world, held from 18 to 20 October 2019 in Rome, Eni presented its wave power projects. On its offshore platform near Ravenna, it has set up the Inertial Sea Wave Energy Converter (ISWEC), in collaboration with the Politecnico di Torino and its company Wave For Energy. The system not only produces wave energy, but could transform offshore drilling platforms in the future into real hubs for generating renewable energy. But how does it work? A small hull is placed in the sea and rocked back and forth by the waves. This movement is registered by a gyroscopic system inside it, and the motion produced is used to generate energy. That is not all. The machine can be attuned to sea conditions and has no mobile parts in contact with the external, which makes it immune to wear and corrosion. ISWEC is therefore particularly suited to capturing Mediterranean waves, as they are lower than those on the ocean. It is also more energy-efficient; the prototype had a peak output of more than 51 kW and the real thing promises to improve massively over successive versions.
The carpet converter
Also on show at the Maker Faire was the PowerBuoy, designed by Ocean Power Technologies in collaboration with Eni. It is a device for converting wave energy into electricity which is then stored in the internal battery, and, which can function in the ocean at any depth between 20 and 1,000 metres. Naturally, Eni is not the only company coming out with systems that exploit wave energy ever more efficiently. One of the most recent offerings comes from the University of California, Berkeley, in US, and takes the form of a carpet 20 metres below the sea surface. Mohammad-Reza Alam, an engineer, got the idea after observing muddy seabeds, which are excellent at absorbing waves. The carpet converter is made up of a sheet of smooth rubber, lying near the seabed, which bends with the waves. As it rises and falls, the carpet works a piston pump, which converts the movement into electricity that goes through a cable to the grid. Another system, designed by SINN Power, operates right on the coast, and consists of a modular structure hung, for example, on harbour walls. The buoy at the bottom moves up and down with the wave motion, producing energy that is fed into the grid.
Union makes clean energy
These systems may all be different, but they share a single aim, namely making the most of a massive yet unexploited source of clean energy. But “clean energy” is not the only rallying cry of our times. Another, perhaps equally, important one is the “circular economy”, and how can cumbersome things like offshore oil and gas platforms, coming to the end of their working lives, possibly fit into a production cycle? In response, rather than removing them and restoring the seabed to its former state, certain projects are looking to turn platforms into artificial coral reefs, giving them a new life in the service of environmental sustainability. One such project is Eni’s “PLaCE”, off the coast of Abruzzo. Using electrolysis technology, it encourages minerals to grow around the platform, not only protecting it from corrosion but providing new, cheap and sustainable material for building. Moreover, the project will create an autonomous marine ecosystem, inhabited by molluscs and sea cucumbers, and provide energy to the platform from renewable sources.
Microalgae absorb CO2 and convert it
At the Maker Faire, Eni also showed the biofixation technology, by which microalgae absorb CO2 and convert it into dry biomass – up to 650 tonnes of it per hectare per year – which can be used in food and cosmetics, as well as advanced biofuels. In short, biofixation means removing CO2 from the atmosphere and putting it back into the production cycle, within a perfect circular economy. From wave motion to algae via re-used platforms, the environmentally sustainable road to the future has an unpredictable course. Yet it is only by taking paths still untravelled that we will overcome the greatest challenges of our age, those of lowering emissions, protecting the environment and preserving a future for ourselves and the planet.
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