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Climate change and energy

Why Hasn’t Tidal Power Taken Off?

Judging by the sheer force of the waves during a day at the beach, the ocean seems like an abundant source of renewable energy. Indeed, more than 70 companies have developed technologies to generate electricity from the changing height of the tides or the kinetic power of waves. Other companies are exploring novel methods of generating electricity from the ocean’s salt content or temperature. Ocean energy has the potential to provide hundreds of gigawatts of power worldwide; the U.K. and U.S. have said that these technologies could provide 20 and 15 percent of their electricity consumption, respectively. But even though companies and governments have invested millions in these technologies over the years, the power generated from the ocean is miniscule, a 2013 Ernst & Young report shows. Here are some of the challenges.

Expensive to build

The most mature form of tidal power, known as tidal range technology, generates electricity from the differences in height between a reservoir and a sea as tides ebb and flow. The first power plant to use the technology was built on the Rance River in France in the 1960s. This required building a large dam-like structure known as a barrage to cordon off an estuary from the sea; the structure also serves as a bridge for cars. As the tides change, the water flows through turbines housed in the barrage. Only a handful of such installations are up and running, with most of the capacity coming from the 240-megawatt Rance River plant and a 254-megawatt power station in Sihwa, South Korea, that has been in operation since 2011.

According to a report from the World Energy Council and Bloomberg New Energy Finance, electricity generated from the movements of the ocean cost two to nine times as much as the highest average price for wind energy in Europe. Because these cost estimates only come from a handful of plants, however, it is hard to gauge how much these technologies could cost in the future.

The high cost comes largely from the extensive engineering work necessary to build the power plants, install them, and connect them to the power grid. Many companies have proposed technologies that might more affordably harness energy from waves or tides, but many are still undergoing testing and a clearly leading technology hasn’t emerged yet, says Alexis Gazzo, an Ernst & Young partner in France. The lack of developed supply chains for any one technology means that components are very expensive. Even at plants that are already built, the variability of tidal patterns can lower the efficiency of the turbines, according to a brief from the International Renewable Energy Association. Project planners also have to consider additional costs for maintenance and monitoring the plant’s impact on the environment.

The U.K. passed on commissioning a tidal range power station near Cardiff, Wales, after determining it could have adverse effects on wildlife, in addition to finding it would take between four and nine years to build at a cost of up to 34 billion pounds. A study found that the barrage would cause even more water to flow into an estuary, altering habitats for birds and fish.

However, the U.K. is still pursuing other tidal projects. The country approved the MeyGen array off the Scottish coast. That array uses another design to generate power from the tides. Instead of being part of a barrage structure as in the Rance River plant, these windmill-like turbines are placed in an array underwater. The design looks like a submerged version of an offshore wind farm. The water’s current moves the turbines, which generate electricity transmitted to the grid through an underwater cable. So far, the U.K. government and turbine maker Atlantis have secured 51 million pounds in initial funding for the project, which is expected to add nearly 400 megawatts of generating capacity by the early 2020s.

Many of the prime spots for tidal or wave technologies are not near the grid, which means new undersea cables would be required. An ocean research center in the Bay of Fundy, home of the biggest tides in the world, recently finished laying down 11 kilometers of undersea cables to create the world’s biggest transmission line for underwater turbines. The cables will carry enough electricity to power 20,000 homes at peak capacity.

The Takeaway:

Despite investments in tidal or wave power from the U.K. and other countries, the technologies have developed very slowly. Two manufacturers of wave power equipment, Oceanlinx and Wavebob, went out of business last year. And just last month, Siemens sold its tidal power unit. It is still hard to gauge how much ocean-power technologies would really cost if implemented at scale.

Thanks to Dale Tyler for this suggestion. If you have a big technology question, send it to

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Illustration by Rose Wong

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