It’s
estimated that one terawatt of energy could be harvested from tidal movements.
This would be enough to power 10 billion 100-watt light bulbs.
Tidal energy installations are multiplying around the world. In Europe — the
region with most tidal stream capacity — electricity produced by tidal
energy increased by an additional 15 gigawatt-hours in 2019, reaching a total
of 49 GWh. Other countries investing in tidal
energy include Australia, Canada, Japan, Korea, and the U.S.And yet, the idea of tidal energy still hasn’t
taken off globally as an economically sustainable renewable. This is largely
due to a lack of feasible locations and the inherent complexity of constructing
energy installations in turbulent oceans.
With a beguiling array of technologies in the
works to meet these challenges, here’s an overview of where tidal energy is
today:
(credit: Scottish Government)
HOW DOES IT WORK?
Tidal energy is a renewable energy source powered by the natural rise and fall of oceans due to the pull of the moon and the sun and the rotation of the earth. Currently, there are three main ways of harnessing tidal energy:
- Tidal barrage: This method uses a large dam where water spills through turbines similar to those used for producing wind power. The barrage gates open as the tide rises and closes at high tide. The water is then released through the barrage's turbines to create additional energy on its way back into the ocean. Barrages can be constructed across tidal rivers, bays, and estuaries.
- Tidal streams: Here, turbines are installed directly into a fast-flowing stream naturally created by the tide, eliminating the need for the construction of a barrage.
- Tidal lagoons: While less common and generating less power, a tidal lagoon is a body of ocean water that is partly enclosed by a natural or manmade barrier. Turbines harvest energy as the partly enclosed water body is filling and emptying.
ADVANTAGES OF TIDAL ENERGY
- Predictable energy: Unlike solar and wind power, which are rendered ineffective on sunny and breezeless days, cyclical low and high tides are easy to predict. Certain turbine systems also harvest energy from both directions of tidal currents, allowing for uninterrupted energy production.
- High durability: With up to 100 years of working use, tidal energy systems have four times the lifespan of a solar panel which typically has a warranty of 25 years. One of the most common types of tidal power plants — long concrete barrages usually built across river estuaries — can therefore be more economical than wind and solar plants if implemented on a large scale. In France, La Rance tidal power station in Brittany has been generating power for the region since 1966.
- Efficiency: Due to the high density of water, tidal energy systems can produce energy even when passing water is moving relatively slowly.
- Storm proofing: Tidal energy structures could also mitigate coastal flooding from storm surges. While more research is needed in order to properly assess their impact, one 2019 study published in the Journal of Ocean Engineering and Marine Energy suggests that a tidal energy system could have a significant effect if operated correctly.
CHALLENGES
- High costs: Building robust structures to
withstand the corrosion of sea water comes at a high cost. Added to the price
tag is expensive equipment for power generation as well as costs for connecting
the system to the electricity grid. For example, the Sihwa tidal power station
in South Korea — the largest installation in the world — cost an
estimated $298m to build in 2011 and has a capacity of 254MW, according to IRENA. Comparing the construction cost with
the capacity, Sihwa costs $117/kwh and produces electricity at $0.02/kwh.
- Lack of locations: Tidal energy systems
require a very specific set of circumstances to operate efficiently. For
example, the difference between high and low tides must be a minimum of five
meters with current technology, and such tidal differences are only found in
about 40 sites around the world.
- Environmental impact: As with other
marine-based energy systems, we still lack a comprehensive understanding of the
potential impact on the ocean. Researchers are still figuring out the effect of
the tidal barrage and mooring on sea movement and aquatic ecosystems.
Electro-magnetic emissions might also disrupt sensitive marine species such as
sharks, skates, rays, dolphins and turtles.
PROJECTS UNDERWAY
- Storing tidal energy: In Scotland, an initiative from the European Marine Energy Centre plans to combine tidal power with vanadium flow batteries to produce continuous green hydrogen. Located on Eday island, Orkney, the system will store electricity generated by tidal turbines during high power periods and discharge it during low power periods — creating on-demand electricity to turn into hydrogen using a 670kW hydrogen electrolyser.
- First U.S. project: In New York, marine energy specialist Verdant Power has secured the first commercial license for a tidal power plant in the country. An array of three turbines has been installed in New York City’s East River and will provide clean electricity to Roosevelt Island through a distributed generation connection to Consolidated Edison’s local electricity grid.
- Floating tidal system: Canada’s Sustainable Marine has developed a floating tidal energy platform prototype that has already undergone nearly two years of tests on the waters of Grand Passage, Nova Scotia. During comprehensive monitoring, there has not been any evidence of adverse effects on fish or marine life, and construction of three platforms is set to begin in 2021. They are projected to provide up to 9MW of renewable electricity to Nova Scotia's electrical grid.
- Mixing it up: About a dozen technology companies around the world are also looking to add wave and tidal energy to existing offshore wind platforms. They argue that using a single floating base for multiple technologies can help improve the energy yield per unit of area. For example, U.S.-based Excipio Energy has designed a floating platform that can accommodate wind, wave, flow, mooring energy and ocean thermal energy conversion technologies all at the same time. Adding other energy sources to the mix can also complement offshore wind turbines by delivering power during breezeless periods.
