If the location isn’t right for a barrage, it’s also theoretically possible to build a semicircular seawall out into the sea to create a lagoon that traps water—what’s essentially a gigantic, sci-fi sea dam. As the tide recedes, a difference in water level builds between the lagoon and the surrounding water. Once the difference is large enough, sluice gates open so that the water rushes through the gaps and sets underwater turbines in motion. The proposed Swansea project would have done this, albeit on a smaller scale.
Though that lagoon failed to get funding, Falconer is helping to develop another tidal lagoon in the Bristol Channel that could generate 6.5 terawatt-hours of electricity per year. That’s a lot less than the two new nuclear reactors being built up the coast at Hinkley Point, which will generate 25 terawatt-hours a year. But the Hinkley reactors are much more expensive: They’ll cost £26 billion ($29 billion) and last 60 years, whereas the tidal lagoon would cost £8.5 billion and last at least twice as long, Falconer says. Harnessing the power of tidal ranges might be expensive, but the up-front cost could still come in well below other consistent means of energy production, like nuclear.
But tidal projects haven’t just fallen through due to lack of funding—there are environmental concerns too. The UK’s most ambitious tidal proposal—a £30 billion project harnessing the enormous tidal power of the Severn Estuary, which would link the English and Welsh coasts with a barrage—was abandoned in 2010, partly to avoid disrupting birds that feed and winter in the area. (The project has been back on the agenda since March 2022, however, when a coalition of local authorities, businesses, and scientists set up an independent commission to reconsider it.)
Fears that turbine blades can injure marine animals have also been a dampener. In 2021, a 37-year-old tidal power plant in Canada was shut down partly because the Department of Fisheries and Oceans had found that the plant’s turbine was killing fish. Turbines can also disrupt the mixing of water between the seabed and the surface, which is important for cycling nutrients in the sea and sustaining the food web.
But research suggests such environmental costs are, on balance, worth it: In a 2018 study, Michela De Dominicis and her colleagues at the UK’s National Oceanography Center showed that even if some 19,000 turbines were installed in Scottish waters and water mixing was disrupted, this would still have a net positive environmental impact because of the clean energy generated. “We are perturbing the environment by putting many turbines in the water, but at the same time, it’s something that is going to reduce climate change,” De Dominicis says.
Yes, tidal power remains expensive, but then so were solar and wind power just a few years ago. Then along came subsidies, up went investment and adoption, and the rest is history. And unlike so many other renewable energy sources, tidal has one big advantage: The sea never stops churning. “Tidal energy can complement wind and solar to provide benefits to the energy system as a whole,” says Coles.