Harnessing the ebb and flow of the United Kingdom’s tides holds the potential to reduce dependence on fossil fuels.
While strides have been made in wind and solar technologies, the need for a comprehensive renewable energy portfolio necessitates tapping into tidal power.
The UK, surrounded by some of the world’s most powerful tides, is uniquely positioned to exploit this abundant resource.
“Tidal power has really significant potential,” says Dr Amanda Smyth from the University of Oxford, “yet it has never been developed at scale.”
She believes that is set to change.
British companies are spearheading innovations, including an underwater kite that maximises rotor speed.
Tides, influenced by the moon’s gravitational pull, offer a dense and predictable energy source. Water, nearly 1,000 times denser than air, concentrates energy efficiently.
Unlike wind and solar power, which depend on weather conditions, tidal power provides a consistent and reliable energy stream. Studies suggest tidal generation could meet up to 11% of the UK’s annual electricity demand.
Historically, the potential of tides was recognised, with examples like the Woodbridge Tidal Mill in Suffolk, operational for almost a millennium. However, larger dams or barrages, constructed for electricity generation, raise environmental concerns and were rejected due to their impact on water flow and marine life.
Fish can be blocked into or out of the lagoons barrages and dams create, and can get caught in the blades of the turbines.
“That’s a really important consideration,” says Dr Smyth. “Especially when we’re thinking about a renewable source of energy that we want to be good for the environment. We do need to consider the full ecosystem impact.”
These concerns – and the huge cost – are why a £25bn proposal to build a barrage on the Severn Estuary between Somerset and Wales was rejected a decade ago.
They is why much of the focus of tidal power research has moved to the energy contained in tidal streams – the currents of water created by the rise and fall of the tides. These run fastest where constrictions, like straits or inlets, funnel the water, increasing the speed of the flow.
The UK, a leader in tidal stream research, tests various devices, from turbines on the seafloor.
Situated 20 miles north of the Scottish mainland, the Orkney Islands boast extreme tidal streams, making them an ideal location for the European Marine Energy Centre established two decades ago.
Among the innovative tidal projects, MeyGen, a Scottish company, is implementing a straightforward design by installing a significant array of turbines on the seafloor. Each turbine, featuring three 16-meter blades, harnesses energy as water flows past.
In contrast, the Orbital O2 adopts a distinct approach, presenting an enormous yellow lozenge moored to the seafloor with two giant turbines resembling wings. Weighing 680 tonnes, this turbine, considered the world’s most powerful tidal stream system, floats on the surface with rotors submerged, capable of fulfilling the electricity needs of 2,000 homes according to its developers.
In the Faroe Islands, engineers are testing the Minesto “Dragon,” a groundbreaking concept. Utilizing tidal currents, this submersible ‘kite’ mimics the aerodynamics of a flying kite, achieving increased speed underwater in a figure-of-eight pattern. Tethered to the seabed by a cable, the Dragon not only generates electricity but also showcases an innovative approach to harnessing tidal energy.
Harnessing tidal energy often occurs in remote areas, minimising local opposition due to submerged equipment in these fast-flowing tidal streams.
While turbines, according to Dr. Smyth from Oxford University, pose minimal threats to marine life in terms of speed, noise can disturb animals, limiting their feeding areas.
The primary challenge is the high cost of tidal projects, reflecting the harsh marine environment’s engineering complexities, with waves and currents posing maintenance difficulties and saltwater corroding metals. D
espite these obstacles, proponents draw parallels with significant cost reductions in wind and solar technologies, anticipating similar declines in tidal power costs as the industry matures and grows.
Tidal power’s predictability distinguishes it, eliminating the need for expensive backup power supplies. Government subsidies, exemplified by a recent deal guaranteeing a high purchase price for tidal electricity, aim to foster industry growth and cost reduction.
That said, it will always be pricier than its rivals, warns Dr Danny Coles, a tidal power expert at the University of Plymouth.
“Because tidal turbines are restricted in size due to the depth of water, they will never achieve the sort of economies of scale that wind has been able to achieve,” he said.
Maintaining and operating machinery fully submerged poses more challenges than offshore wind turbines.
The question arises: how can this be economically viable?
The answer lies in the predictability of tides. Unlike the uncertainties of wind and solar power, tidal energy’s reliability eliminates the need for expensive backup power, typically provided by gas-powered plants in the UK. Tides follow a predictable pattern regardless of weather conditions, ensuring tidal generators can offer consistent power without backup.
Recognizing this potential, the government is providing substantial subsidies to companies advancing tidal technology. The aim is for government support to foster growth in the tidal power industry, leading to significant cost savings.
Dr Coles is confident significant amounts of the UK’s power will be generated from tidal energy industry in 20 years’ time.
“That’s going to really benefit the energy system as a whole,” he says.
However, a cautionary note: tidal energy isn’t entirely renewable. The ebb and flow of tides create friction between ocean waters and the seabed, exerting a minuscule drag on the Earth’s rotation, contributing to a gradual slowing and lengthening of our days.
Though tidal energy systems introduce a minute additional drag, the effect is infinitesimal. Scientists estimate that tidal drag has extended the day from 21 to 24 hours, a process spanning six hundred million years.
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