Saudi Arabia in the North Sea

The tides that tear through the Pentland Firth are among the fastest in the world.

The currents, which pass through the 6-mile-wide strait between the Scottish mainland and the Orkney Islands and connect the North Sea to the Atlantic Ocean, rip through at more than 11 miles per hour. It is here, in these chilly gray-blue waters, that Scotland hopes to find its energy future — not in oil beneath the ocean floor, but by harnessing the power of the waters themselves.

This ought to be one of the world’s best sites for tidal-power development, thanks to the speed of the currents, the not-too-deep seafloor, and the not-too-far distance from the country’s energy grid. In 2006, Alex Salmond, who would later go on to become Scotland’s fourth first minister, dubbed the stretch of ocean “the Saudi Arabia of tidal power.” In theory, the Pentland Firth alone could generate almost half the electricity currently consumed in Scotland, according to a study led by Oxford University researchers.

If, that is, the engineers could figure out how to pull it off.

Over the next two years, MeyGen, the company behind a trailblazing project to harness the potential of the Pentland Firth’s turbulent waters, plans to install four turbines on the seafloor. Like modern wind turbines, but driven by water rather than air, the array (as the cluster of turbines is called) will churn with the clockwork rhythm of the tides. And if all goes well, the array could expand to as many as 269 turbines, making it the world’s largest tidal-stream energy project. To a large degree, the future of tidal power — one of the most promising, but also one of the most quixotic energy sources — is riding on the success of these ambitious plans. By 2016, MeyGen expects to start sending power from the turbines to the onshore grid. Electricity generation could ultimately grow to a capacity of almost 400 megawatts — enough to power 175,000 Scottish homes, according to MeyGen.

Humans have been capturing energy from the tides since at least the mid-1800s. They trapped water behind dams and released it through water wheels that used the energy to turn grain-grinding millstones. But despite its long history, tidal power never became a major part of the world’s energy mix. Today, it accounts for less than 0.001 percent of the global energy supply. It remains one of the most challenging forms of renewable energy, not just because of the difficulty of operating and maintaining equipment in unforgiving conditions — working underwater is tricky and expensive — but also because of concerns about impacts on marine life and industries such as fishing and shipping. Nevertheless, interest and investment have surged in recent years, in large part because of concerns about climate change.

It’s easy to see the appeal of tidal power. It has a carbon footprint comparable to that of wind power, but with a couple of major advantages: The turbines are hidden beneath the waves, where they can’t spoil any views, and the tides are far more predictable than wind. As the water moves, it turns turbines that produce power. The more water passing through the turbines in a given period of time, the more power that can be generated.

But like the wind industry a few decades ago, tidal-stream development is going through some growing pains. Just as solar power capacity has recently exploded — growing more than tenfold since 2000 — after years of slow evolution as technology improved and costs went down, tidal energy could follow a similar path to become a major source of green power.

The first commercial tidal-power station was built on the Rance River in France more than 50 years ago, and now more than a half-dozen commercial tidal-power stations are in operation, including a 254-megawatt one in South Korea that came online in 2011. The 1,320-megawatt-capacity Incheon Tidal Power Station, currently under construction in South Korea, will be the world’s biggest when it is completed in 2017.

These tidal-power stations, however, use a different, more mature technology than the projects planned for Scotland’s coastline. While the MeyGen project will plant turbines on the ocean floor in the path of fast-running tides, the French and South Korean projects instead use a dam-like barrage built across a river, estuary, bay, or artificial lake. These bodies of water fill as the tide rises and then release water through hydropower turbines when the tide falls, to generate electricity.

The United Kingdom is the world’s leader in the cutting-edge tidal-stream technology. The island nation sees not only an opportunity to exploit its own abundant tidal resources, but also a chance to capture a big share of the potential world market for marine-energy technology. Those hopes are now pinned on MeyGen’s Inner Sound project, the biggest of nine tidal-power projects planned for the Pentland Firth and Orkney Waters Marine Energy Park, one of two such parks established during the past three years in the United Kingdom. The project is “still at an early stage of development,” according to the company, and will continue to unfold only if each step in its phased approach is successful.

Still, tidal-energy projects could help the U.K. meet its European Union mandate of generating 15 percent of its electricity from renewables by 2020. The government estimates that wave and tidal-stream energy combined could eventually provide as much as 20 percent of the U.K.’s electricity. By the end of 2013, though, the U.K.’s total installed capacity of both wave and tidal energy was a mere 7.2 megawatts.

Energy development in the Pentland Firth is still in its infancy, and tidal-power projects there — and elsewhere — have some major obstacles to overcome. Although prototypes of tidal-stream turbines have been deployed, development has proceeded in ebbs and flows, and the technology has yet to be demonstrated on a fully commercial scale. In the United States in 2012, Verdant Power received the country’s first commercial tidal-power license from the Federal Energy Regulatory Commission to construct a pilot project in New York City’s East River, which connects Long Island Sound with the Atlantic Ocean. Verdant has permission to install up to 30 of its fifth-generation tidal-stream turbines, with a total generating capacity of about 1 megawatt, beginning this year.

As with most new technologies, the technical challenges have been greater than initially expected. Dozens of turbine designs are vying for attention, but no clear victor — one proven to be reliable, durable, efficient, and cost-effective — has yet emerged.

There are high capital costs for such a project, and there are many uncertainties about whether turbines can withstand harsh conditions without breaking or corroding. When Verdant installed two of its first-generation turbines in New York’s East River in 2006 for a demonstration project, the currents were stronger than expected and the blades failed within a day.

Creating the onshore and offshore infrastructure necessary to connect turbines to the grid is also a challenge. Laying cables and securing turbines in Scotland’s frigid, fast-moving water won’t be easy.

As promising as tidal-stream power is, it remains costly and will require government support to succeed, even at sites with the world’s best tidal-energy resources. Some of the current U.K. support comes in the form of direct funding, as with the MeyGen project. Some of it comes as research and development support for tidal-power developers. And then there’s the Saltire Prize, 10 million pounds from the Scottish government that will go to “the individual, team or organisation that achieves the greatest volume of electrical output over the set minimum hurdle of 100 gigawatt hours over a continuous two year period, using only the power of the sea,” according to the prize’s website. MeyGen is one of four contestants vying for the prize, which will be awarded in July 2017. “It’s a tough challenge, but we are in it to win it,” MeyGen CEO Dan Pearson says.

If tidal-stream energy cannot succeed in Scotland, which not only has strong tides but also strong government support for clean energy, it’s unlikely to succeed elsewhere. But if the MeyGen project manages to dispatch power to the grid without any major problems, that would send a strong signal to investors, utilities, and politicians that tidal power can join the growing portfolio of viable renewable energy sources. Says Pearson: “We are fully aware of how much the sector is counting on our success.”

Andy Buchanan/AFP/Getty Images