Tidal turbines put a new spin on the power of the ocean

The demand for reliable sustainable energy is on the rise. While wind and solar receive a lot of attention, both of these sources have one major drawback: intermittency.

Given the issues with long-term energy storage from renewables, there are plenty of days when the sun doesn't shine and the wind doesn't blow, which means power generated by solar panels and wind turbines might halt. As a result, many countries have remained steadfast in their reliance on fossil fuels. After all, it isn't necessary to burn coal or pump natural gas on a lovely day.

However, some corporations and organizations are now considering a novel option: ocean turbines, which generate power from tidal variations rather than winds. Because the ocean never stops moving, capturing its energy might supply the baseload, or consistent stream of electricity, that other renewables can't match. IHI Corp engineers tested a 330-ton tidal turbine prototype on the seafloor near the Kuroshio Current last month. According to Japan's New Electricity and Industrial Technology Development Organization, this current alone could generate 200 gigawatts of energy via underwater turbines, accounting for 60 percent of the country's producing capacity.

This follows the UK's successful connection of Orbital Marine Power's about 700-ton tidal turbine to the electrical grid in Orkney, Scotland, last year. In addition, four tidal turbines in Scotland provided the longest run of uninterrupted electricity from the new technology in 2019, powering about 4,000 households.

Here's all you need to know about this rapidly expanding form of sea-based energy.

How tidal turbines work

The architecture of these turbines is actually extremely simple—practically it's precisely how you'd expect a wind turbine to work.

“Whether the medium is water or air, it is the same engineering field and the same equations that are used to determine the geometry and effect of the turbine,” explains Petter Karal, CEO of Seatower AS, which provides foundations for offshore wind turbines.

The moon's gravitational pull on the planet creates "tidal force," which causes the planet's and its water to bulge out on the sides closest to and farthest from the moon. Because the Earth and the moon travel through this point twice on their orbits, these bulges cause "high tides" on various beaches twice a day. The currents shift as the tides change. The tides influence and may be predicted by currents, which are the left-to-right flows of water (but can also be affected by factors like water temperature, salinity, and wind). Consider them to be underwater gales.

The power source for sea-based turbines is these fluxes under the water's surface. Tidal turbines revolve and create power as currents pass past them. (Karal observes that the machines resemble ship propellers more than normal wind turbines.) The turbines can also work at a variety of depths: The most modern Japanese model is anchored to the seabed, while some versions, like as Scotland's Orbital Marine Power, float and utilize robotic legs to harvest energy from the ocean's upper layers.

Benefits and obstacles of tidal energy

The moon will continue to revolve around the Earth indefinitely (and if it does, we have bigger problems to think about than turbines). This makes tidal energy a strong contender for renewable energy, especially because climate change hasn't had a significant enough influence on currents to render tidal energy wholly unpredictable. Furthermore, study from 2004 projected the overall worldwide energy potential of tidal power to be at 3,000 gigawatts.

The influence on marine fauna and ecosystems appears to be negligible as well. Sea species and local birds were determined to be unaffected by tidal turbines after 10,000 hours of wildlife observation, according to research from the European Marine Energy Center in Scotland. Because water is denser than air, the turbines don't need to spin as rapidly to generate electricity, which alleviates some of the issues. In addition, Orbital Maritime is doing research into the impact of its O2 tidal turbines' acoustics on nearby maritime habitats.

However, as appealing as they may appear, tidal turbines are not without their drawbacks. For one thing, they can't be placed just anywhere in the water: the finest spots are along the coasts of the British Isles, between the Channel Islands and France, and in the Straits of Messina between Italy and Sicily. Other hotspots include Southeast Asia's island areas, Greek island channels, and Canada's island-filled shores.

Another stumbling block is maintenance. After all, these massive constructions (the Orbital Marine turbine, for example, is around 240 feet long) must be able to withstand the harshest conditions and will need to be repaired on a regular basis. This can be expensive for turbines installed at the bottom of the sea.

“An issue with that is it can cost thousands, if not hundreds of thousands, (of dollars and [require] days and weeks of time to service these turbines,” explains Sarah Clark of Orbital Marine Power. “No matter what your technology is, it’s going to need servicing at one point or another, even if it’s just getting barnacles off the side of the blade.”  

Furthermore, because there is no one-size-fits-all approach to developing alternative power sources, it can be costly to test them and gain industry support. Not to mention the difficulties of obtaining country-by-country licenses to build massive turbines at the ocean's bottom.

Other forms of renewable energy, however, encountered some of the same challenges not long ago. If tidal turbines can provide power 24 hours a day, seven days a week with almost no emissions, it may be time to take those steps.