Using the power of the tides, energy is produced from the gravitational pull from both the moon and the sun, which pulls water upwards, while the Earth’s rotational and gravitational power pulls water down, thus creating high and low tides.
This movement of water from the changing tides is a natural form of kinetic energy.
All it takes is a steam generator, tidal turbine or the more innovative dynamic tidal power (DTP) technology to turn kinetic energy into electricity. Engineering company SIMEC Atlantis recently designed the world’s largest single-rotor tidal turbine, which can generate more electricity at a lower cost of operation and maintenance.
However, tidal currently isn’t the cheapest form of renewable energy, and the real effects of tidal power on the environment have not yet been fully determined. Here are some tidal energy advantages and disadvantages that must not be overlooked.
Advantages of tidal energy: clean and compact
Tidal power is a known green energy source, at least in terms of emitting zero greenhouse gases. It also doesn’t take up that much space. The largest tidal project in the world is the Sihwa Lake Tidal Power Station in South Korea, with an installed capacity of 254MW. The project, established in 2011, was easily added to a 12.5km-long seawall built in 1994 to protect the coast against flooding and to support agricultural irrigation.
Even solar farms are usually bigger, such as the Tengger Desert Solar Park in China that covers an area of 43km2 and the Bhadla Industrial Solar Park that is spread across 45km2 of land in Rajasthan, India.
In this respect, even small countries with a long enough stretch of coastline can utilise tidal power in ways that they could not otherwise compete with land-rich countries like the US, China, and India on solar and wind.
Advantages : continuous, predictable energy
Another benefit of tidal power is that it is predictable. The gravitational forces of celestial bodies are not going to stop anytime soon. Furthermore, as high and low tide is cyclical, it is far easier for engineers to design efficient systems, than say, predicting when the wind will blow or when the sun will shine.
In June 2018, Bloomberg reported that the UK went nine days without generating almost any wind power. From 26 May to 3 June, power generated from UK wind farms fell from more than 6,000MW to less than 500MW. In contrast, scientists already know the volume of water and the level of power the tidal equipment will likely generate before construction.
Tidal power is also relatively prosperous at low speeds, in contrast to wind power. Water has one thousand times higher density than air and tidal turbines can generate electricity at speeds as low as 1m/s, or 2.2mph. In contrast, most wind turbines begin generating electricity at 3m/s-4m/s, or 7mph-9mph.
Moreover, technological advances in the industry will only drive cheaper and more sustainable tidal power solutions.
“Historically, wave energy converters have been costly and large compared to their energy output. But we shouldn’t let that define the future of the tidal industry. Around 10%-20% of global electricity demand could be met by wave power,” says Diego Pavia, chief executive officer at InnoEnergy.
“It’s a very predictable energy source and typically offsets the intermittency of solar and wind – balancing the grid with a low levelised cost of energy. One of our assets, CorPower, is challenging how the industry thinks about wave energy by using principles of the human heart. Through its wave energy converter, the company is able to deliver five times higher wave energy absorption than other technologies. And that’s why the power of wave energy should not be overlooked.”
Advantages: longevity of equipment
Tidal power plants can last much longer than wind or solar farms, at around four times the longevity. Tidal barrages are long concrete structures usually built across river estuaries. The barrages have tunnels along them containing turbines, which are turned when water on one side flows through the barrage to the other side. These dam-like structures are said to have a lifespan of around 100 years. The La Rance in France, for example, has been operational since 1966 and continues to generate significant amounts of electricity each year.
Wind turbines and solar panels generally come with a warranty of 20 to 25 years, and while some solar cells have reached the 40-year mark, they typically degenerate at a pace of 0.5% efficiency per year.
The longer lifespan of tidal power makes it much more cost-competitive in the long run. Even nuclear power plants do not last this long. For example, the new Hinckley Point C nuclear plant planned to be built in Somerset, UK, is estimated to provide power for around 60 years, once completed, according to a BBC report.
Disadvantages of tidal energy: lack of research
While the true effects of tidal barrages and turbines on the marine environment have not been fully explored, there has been some research into how barrages manipulate ocean levels and can have similar negative effects as hydroelectric power.
A 2010 report commissioned by the US National Oceanic and Atmospheric Association and titled ‘Environmental Effects of Tidal Energy Development’ identified several environmental effects, including the “alteration of currents and waves”, the “emission of electro-magnetic fields” (EMFs) and its effects on marine life, and the “toxicity of paints, lubricants and anti-fouling coatings” used in the manufacturing of equipment.
The Pacific Northwest National Laboratory (PNNL) studied the effect of a tidal turbine at Strangford Lough off the coast of Northern Ireland. The PNNL’s Marine Sciences Lab was particularly interested in how the tidal turbine affected the local harbour seals, grey seals, and harbour porpoises that inhabit the area. The Atlantis-manufactured turbine studied was able to turn off when larger mammals approached.
However, there is still a need for further research.
“The ocean’s natural ebb and flow can be an abundant, constant energy source. But before we can place power devices in the water, we need to know how they might impact the marine environment,” said PNNL oceanographer Andrea Copping in a research paper.
“We have to prove beforehand that there is no impact, and we cannot. We have no concrete proof, just theories based on existing knowledge and computer modelling.”
Disadvantages: the impact of EMF emissions
Electro-magnetic emissions might also disrupt the sensitive marine life. Fellow PNNL marine ecologist Jeff Ward said the organisation was observing how EMFs damage the ability of juvenile Coho salmon to recognise and evade predators, or the negative impact on Dungeness crabs to detect odours through their antennules. They are also observing whether sea life is attracted or repelled by EMFs in general.
Ward said at the Oceans 2010 conference: “We really don’t know if the animals will be affected or not. There’s surprisingly little comprehensive research to say for sure.”
While there has not been much research into the effects of EMFs, a European Commission study in 2015 found that EMFs could also have an impact on the migratory routes of sea life in the area.
Particular species that are susceptible to EMFs are sharks, skates, rays, crustaceans, whales, dolphins, bony fish, and marine turtles. Many of these animals use natural magnetic fields to navigate their environment.
The most conclusive study, according to the European Commission’s ‘Environmental impacts of noise, vibrations and electromagnetic emissions from marine renewable energy’, was an observation of migration in eels. The study found that the EMF caused the eels to divert from their instinctual migratory route, but “the individuals were not diverted too long and resumed their original trajectory”.
Another experiment found that benthic elasmobranchs – which includes sharks, rays and skates – were attracted to a source of EMF emitted from a subsea umbilical. Again, there was no conclusive evidence of any cumulative, detrimental effects.
Disadvantages: high construction costs
There’s no avoiding the fact that tidal power holds one of the heaviest up-front price tags. The proposed Swansea Bay Tidal Lagoon project in Wales, UK, is priced at £1.3bn ($1.67bn). The aforementioned Sihwa Lake Tidal Power Station cost $560m, and the La Rance cost 620 million francs back in 1966. Using an online conversion and inflation calculator, this was equal to roughly $940m in 2018.
In comparison, The Tengger Desert Solar Park cost around $530m for a total installed capacity of 850MW, making it more cost-efficient than Sihwa Lake, at 254MW total capacity. Likewise, the Roscoe Wind Farm cost around $1bn for an output of 781MW, compared to the Swansea Bay tidal project that is expected to generate around 320MW in total.
While long-term generation costs are relatively good compared to other renewable energy systems, the initial construction cost makes investing in tidal energy a particularly risky venture.
Firstly, installing a tidal system is technologically challenging. Manufacturers are competing against the moving ocean, and the equipment and technical knowledge needed to successfully construct the system is typically very expensive, especially compared to a wind or solar farm.
The second expense relates to the point made in the previous section. Companies managing a tidal power system need to conduct continuous analysis into the effect it has on the specific environment in which they are operating. This requires research and assessment from environmentalists, marine biologists, and geographical experts to mitigate the destruction of sensitive ecosystems, which can be costly.
However, Oregon State University associate professor of energy systems Ted Brekken remains certain that technological progression will help to mitigate some of these costs, telling Yale Environment 360: “The technology has kept moving forward, which is good news. But the big issue is to get the cost down. Right now, there is the reality of surviving while we get there.
“At some point, all the easy, cheap installations for wind and solar will be done. And then it’s ocean energy that’s next in line.”