Future Tense

The Scots Are Unlocking the Ocean’s Energy Potential

A boat and a tidal generator sit in the water with land in the background.
Orbital Marine Power’s O2 tidal energy turbine off the coast of Orkney, at the European Marine Energy Centre in Orkney. Jane Barlow/AFP/Getty Images

Scotland is the source of many great exports: scotch (of course), Gordon Ramsay, and the Young brothers of iconic rock group AC/DC. Its next gift to the world might be a way to harness renewable energy from the ocean.

In April, Scottish-based Orbital Marine Power launched the O2, the world’s most powerful tidal turbine, to be tested off the coast of the Orkney Islands.* Tidal turbines harness the power of underwater currents to turn turbine blades and produce electricity. Jon Kelman, an energy policy instructor at Arizona State University’s School of Sustainability, says this is especially efficient “because water is so much denser than air, you don’t actually need a very big turbine in order to make a lot more electricity.” (Disclosure: I recently graduated from ASU, where I took an energy policy class with Kelman; ASU is a partner with Slate and New America in Future Tense.)

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To wrap your mind around this, think how much harder it is to walk in your pool than in air. This new turbine has a capacity of 2 megawatts and represents a modular technology that could be applied to a virtually untapped renewable resource. For context, it takes roughly 1,130 pounds of coal to produce 1 megawatt hour of electricity in the U.S. That means, if these turbines operate at full capacity, they can replace 2,260 pounds of coal for electricity generation per hour. Power generation devices never operate at full capacity and a singular generator still represents a very small amount of global energy demands—but a flexible fleet of turbines could prove immensely useful at a large-scale.

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Another Scottish company—Mocean Energy—also began sea trials in Orkney last month of its new utility-scale wave power device called Blue Horizon. Unlike O2, this device captures kinetic energy directly from waves on the surface. Both new technologies require further testing but offer the potential of harvesting low-carbon renewable energy from the ocean with minimal impact to the surrounding environment.

These new marine technologies could have a big effect in coastal and island areas without access to much existing renewable infrastructure. Take Hawaii, where each island has its own independent electrical grid and relies heavily on energy imports, creating exorbitant costs and fossil fuel dependence. This is because, as Kelman notes, the Hawaiian islands are “one of the most remote [populated] places on Earth.” However, given minimal land area available for energy generation, solutions can be more difficult to implement than on the mainland. Tidal turbines and wave generators could provide a unique solution for the island state—and coastal communities worldwide. This is even more pertinent for Hawaii, which has set an ambitious goal of having 100 percent renewable energy generation by 2045.

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Estimates of the total available supply of accessible marine energy are variable, but likely represent hundreds—if not thousands—of gigawatts of capacity globally. Wave power resources represent some 2.11 terawatts of supply globally, with academic estimates determining that roughly 5 percent of that total is extractable. For context, based on U.S. Energy Information Administration statistics, the average American home consumes roughly 0.011 gigawatt hours each year. In case your eyes skimmed over all of those statistics: What you need to know is the theoretical supply is immense.

A certain amount of tidal power is already being generated, but current methods of marine energy extraction have significant drawbacks. The historical model for tidal energy has been a barrage—a dam-like structure built across a marine inlet that uses extreme tidal differences to produce energy much like a hydroelectric dam (aka water flow through a turbine). Examples like the Sihwa Lake Tidal Power Station in South Korea and the decades-old La Rance Tidal Power Plant in France use this model for a generating capacity of over 200 MW. However, these plants require extreme tidal variation from high to low tide and are expensive to construct, severely limiting the areas they can be installed. While tidal variation exists everywhere, the necessity of a bay to house the barrage and the dramatic variation required for plants to be economical just aren’t common enough to be a central component of renewable energy generation. Furthermore, they effectively “close off an estuary” which interrupts “ecosystem services that humans rely on,” like reduced stormwater flood management and local water cleaning, according to Kelman. Soils and plants in estuaries absorb floodwater, prevent erosion, and remove sediment and nutrient loads that can lead to eutrophication—which depletes dissolved oxygen in water ecosystems and threatens their health.

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While tidal turbines and wave generators avoid these environmental pitfalls, there are big hurdles to jump through for these marine technologies to be applied on a larger scale. Kelman says, “There are two main questions in regard to tidal turbines.” First: “How cheap can you make it in the future?” Second, “What is the capacity factor?” Capacity factor is a ratio of a power unit’s actual electricity output compared to the maximum possible output over a given period. Many renewables with intermittent supply fail to achieve efficient capacity factors—so finding reliable power sources is key for a clean energy future.

Orbital Marine is working to address both questions. On the cost front, Orbital Marine Power’s commercial director, Oliver Wragg, explains that by the 2030s, the company hopes to “streamline our production processes” so that “we will have accelerated down the cost curve and will be delivering … projects at a cost cheaper than nuclear energy can be produced in the U.K. today.” And while there aren’t exact calculations of the O2’s capacity factor yet, official communications from the company claim that the initial O2 turbine will have the ability to reliably meet the power needs of 2,000 U.K. homes once deployed.

And one thing Kelman and Orbital Marine definitely agree on: A key benefit of this power source is that tides—unlike sunlight or wind speeds—are highly predictable, making the output more predictable as well.

Correction, June 14, 2021: This article originally misstated when Orbital Marine Power launched the O2. It was in April, not May.

Future Tense is a partnership of Slate, New America, and Arizona State University that examines emerging technologies, public policy, and society.

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