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  • This episode of Real Engineering is brought to you by Brilliant. A problem solving website

  • that teaches you to think like an Engineer.

  • Next time you're near the ocean, listen closely to the waves. That sound you hear?

  • That's wasted energy.

  • The energy from waves, tides and currents, known collectively as ocean energy, is a massive

  • resource just waiting to be tapped.

  • The total energy available along the American continental shelf could potentially provide

  • roughly half of the current total US energy supply. [1] With an estimated 250 TWh/yr for

  • the West Coast, 160 TWH/yr for the East Coast, 60 TWh/y for the Gulf of Mexico, 620 TWh/y

  • for Alaska, 80 TWh/yr for Hawaii, and 20 TWh/yr for Puerto Rico. [1]

  • Harassing all of that energy, while transporting it to population centres and finding suitable

  • locations along the coast that will not affect coastline ecosystems and property values would

  • be a difficult if not an impossible task, but if we could find a suitable way to harass

  • the power of the tides and waves off our coasts, it could provide the final push needed to

  • convert out grid to a 100% renewable system [2]

  • There are many methods to gain energy from the sea. Wave power is created as the wind

  • pushes the surface of the ocean. Ocean currents provide power driven predominantly by wind

  • and heat from the sun. Some systems have even utilized the differences in salinity between

  • rivers and seas to produce electricity.

  • However, today we are going to investigate one of the most promising technologies in

  • this sector, Tidal Energy. It has huge potential in the renewable energy market thanks to its

  • predictable and consistent availability. Tides change four times a day, every day.

  • This is a result of the Earth rotating through bulges of ocean water formed by the gravitational

  • influence of the Sun and Moon. We experience greater tides, called Spring Tides, when the

  • Sun is aligned with the Moon allowing their gravitational influence to combine. [3] This

  • corresponds to the New and Full Moon phases of the Moon. And we experience smaller tides,

  • and smaller differences in high and low tide, during Neap Tides. This occurs when the Moon

  • is at a quarter phase, offset to the Sun by 90 degrees. Meaning our tides are not only

  • smaller in total, but the changes in tide are minimised.

  • While their intensity does vary, these tidal changes come 4 times a day and result in a

  • flow of water that will look something like this for a Spring Tide and this for a Neap

  • Tide. [4] With the Spring Tide not only resulting in a higher tide, but a faster flow of water,

  • which means more energy is available for extraction.

  • These patterns can be projected well into the future thanks to the predictable movement

  • of the Sun, Moon and Earth. Which definitely cannot be said for the unpredictable weather

  • here on earth which affects Wind and Solar energy.

  • Despite this steady and reliable flow of water, ocean power provides the smallest percentage

  • of renewable energy. With only two large scale tidal energy plants, a 240 MW system [5] located

  • in the estuary of the Rance River in Northern France, and a 254 MW system in Sihwa Lake

  • in South Korea [6]. Both are tidal barrage systems, which work similarly to dams by opening

  • and closing sluice gates to control the flow of water through their turbines. This is a

  • proven technology, proving they can generate electricity and operate in seawater without

  • corrosion being a massive issue thanks to cathodic protection. [7]

  • So why are there so few of these systems in the world. The problem is two-fold. First,

  • the cost of installation is incredibly high requiring a very large structure to control

  • the flow of water. It simply makes more sense to use other forms of renewables like wind

  • and solar. And second, a large barrier like this has a significant effect on the local

  • ecosystem.

  • One company, Simec Atlantis, is looking to improve on both of these points with their

  • underwater turbines which look remarkably like normal wind turbines, but thanks to water's

  • higher density can be much smaller.

  • Their first prototype system was placed here in the mouth of Strangford lough in Ireland.

  • This area benefits from some of the fastest flowing water in Ireland, as tides force their

  • way in and out of the bottleneck of Strangford Lough. Millions of tonnes of water flow through

  • the channel every day. [8]

  • The system consisted of two 16 metre diameter turbines with a nameplate capacity of 0.6

  • MWs each. [8] For reference an equivalent wind turbine would have a diameter around

  • 40 metres. These turbines reached full capacity in November 2008 and were decommissioned in

  • May 2016. [9] If that 1.2 MWs ran continuously at full capacity for all that time it would

  • result in about 77-79 GWhs of power, however it only produced 11.6 GWhs. [10] Enough to

  • power around 1 thousand American homes for 1 year, but that's just 15% of its full

  • potential. That percentage is called a capacity factor and 15% is a very low capacity factor,

  • with Ireland's 5 year average wind energy capacity factor standing around 28%. [11]

  • However this was a prototype which did not run continuously and was routinely taken offline

  • for inspection and research. In their best month, SeaGen produced 522 MWhs with a capacity

  • factor of 59% and Seagen claim that is reproducible year round. [12] With a capacity factor of

  • 59% year round this would make tidal energy an incredibly reliable energy source with

  • only minimal storage needed to smoothen out the peaks and troughs between the tides. With

  • a short time between peak power generation and minimum power generation, this form of

  • tidal energy could use cheaper short-term energy storage solutions like mechanical batteries

  • to create a desperately needed renewable baseload.

  • This project was decommissioned in 2016, as part of the research process. It was vitally

  • important to test whether these machines could be effectively removed from the environments

  • with minimal impact. [13] And this is of course a major concern for any machinery being placed

  • into a marine environment. Seagen satisfied this requirement having no significant effect

  • on the local ecosystem, and they have since moved onto the next stage of their technology

  • with Meygen, installed in between the Island of Stroma and the North East coast of Scotland.

  • Their original lease agreement was for up 400 Megawatts, provided the initial testing

  • phase with 4 turbines satisfied the environmental impact requirements. [14]

  • The latest version of the underwater turbine now has 3 turbine blades, allowing for an

  • increase in capacity to 1.5 MegaWatts with only a slightly increased diameter turbine

  • over the 16 metre 0.5 MegaWatt turbines of their previous project in Northern Ireland.

  • This turbine is also completely submerged, so it is not an eyesore for local residents.

  • Seagen previously had actuators to lift the turbine out of the water to allow maintenance

  • to occur, but the new generation of turbines are designed so the actual turbines and generators

  • can simply be placed and removed from the substructure in about 30 minutes. [15] Making

  • installation and maintenance vastly easier and cheaper.

  • Environmental impact has been a central focus for the project and this started with a comprehensive

  • survey of the surrounding ecosystem from seaweed and shellfish to the whales that occasionally

  • visit the area.

  • The area thankfully has such fast moving water that the seabed was stripped of sand and silt,

  • so the installation had little impact on ecology of the rocky seafloor.

  • The impact the installation could have on local marine mammals was of much larger concern

  • with surveys showing a large population of both seals and dolphins, with several haul

  • out areas for seals nearby. [16] Both of these mammals are sensitive to noise and will likely

  • avoid any area with excessive sound. The noise levels these turbines emit are not terribly

  • high, as they move relatively slowly through the water. Their 544 page long environmental

  • report, which I read to the best of my ability in the 1 week of research I did for this video,

  • indicates that seals will have a strong avoidance of the noise within 38 metres of the structures,

  • while mild avoidance may extend as far as 168 metres. [17] With seal haulouts over a

  • kilometre away this was deemed acceptable. While dolphins are expected to avoid the noise

  • up to 100 metres and filter feeders like whales up to 500 metres, which may remove a small

  • section of sea from use, but will not act as a barrier to any significant feeding ground.

  • A significant improvement over tidal barrages.

  • This theory is backed up by surveys conducted during Seagen's operation which found little

  • evidence that the two turbines had a significant effect on the numbers of seals and dolphins

  • during operation, but did have an effect during the construction phase where noise was much

  • higher. [18]

  • Area avoidance would be useful in the fact that it would prevent the animals from straying

  • too close to the turbines and being struck by them. Potentially hurting themselves and

  • damaging the turbine. Once again we can garner some positive data from Seagen, which examined

  • all carcasses discovered near the site and found no evidence that any deaths were caused

  • by impacts to the turbines. [19]

  • This seems unlikely but they theorize that these animals actually avoid the areas while

  • the turbine is operating not because of sound, but because the water is flowing fast enough

  • to make it too difficult to swim and catch prey.

  • The last major worry for these types of devices is the fact that they need to use toxic anti-fouling

  • coatings to prevent marine growth on the turbines. However Meygen uses a clever low friction

  • paint that self cleans as soon as the marine growth grows large enough where the drag overcomes

  • their ability to adhere to the slippery paint.

  • Additionally they trialed a sonar detection system that would allow them to track and

  • potentially stop the turbines when larger animals occasional pass through the area.

  • Without a doubt, these types of turbines would have less of an impact on the environment

  • than tidal barrages seen in France and South Korea, but only time will tell whether this

  • system in the far reaches of Scotland will have a small enough impact to encourage additional

  • systems to be installed.

  • Cost will still be a massive factor. Based on their companies financial reports the Meygen

  • project generated 2.7 million dollars of revenue for the company in 2018. That's 0.675 million

  • dollars of revenue from each turbine. Based on their estimated cost for a further 49 turbines

  • at 540 million dollars, we can calculate that each would come with an installation cost

  • of around 11 million dollars, so that would require 16.3 years to recoup the cost of installation.

  • Which is better than the 20 years it took to recoup the costs of tidal barrage system

  • in France, and those numbers will likely continue to drop if the company manages to start manufacturing

  • these underwater turbines on a larger scale.

  • But it's slow going. Iterating and improving on designs for tidal power is much more difficult

  • than other forms of renewable energy. Testing has to take place in coastal waters, most

  • of which are public spaces, requiring extensive permitting and testing.

  • It's unlikely that these underwater turbines will ever compete on cost with onshore wind

  • turbines or solar, but thanks to the predictability of the tides this form of energy could provide

  • a reliable baseload when combined with low cost batteries.

  • If this project succeeds if could justify large scale manufacturing of these turbines

  • and transform tidal energy from a small niche industry, to a huge player in the renewable

  • energy industry.

  • After all, Meygen is just one small section of a larger 1600 MW ocean energy project earmarked

  • for Pentland Firth and Orkney, with mixes of both wave and tidal energy.[20]

  • A colossal amount of energy which could go a long way to diversifying Scotland's power

  • usage, and we will delve into the world of wave energy in a future video.

  • In the meantime, you can learn more about other forms of renewable energies like solar

  • by watching some of my past videos on the topic, or taking this course on solar energy

  • on Brilliant. Or even better mark off one of your Christmas gifts and give the gift

  • of life long learning to one of your loved one by gifting them a Brilliant Premium subscription.

  • If you know anyone who has a passion for math and science this is a great gift that will

  • nurture their curiosity, build confidence and help develop vital problem solving skills

  • crucial for school, job interviews and in their carrier.And Brilliant's thought-provoking

  • content breaks up complexities into bite-sized understandable chunks that will lead them

  • from curiosity to mastery.

  • This obviously works, because I had someone from Tesla contact me this week telling me

  • they took this course on solar energy in preparation for an interview for Solar City.

  • If I have inspired you, go to brilliant.org/realengineering and grab a gift subscription to help your

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  • As always, thanks for watching and thank you to all my Patreon supporters. If you would

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  • below.

This episode of Real Engineering is brought to you by Brilliant. A problem solving website

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B2 US energy tidal turbine capacity renewable water

Can Underwater Turbines Solve Our Energy Problems?

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    joey joey posted on 2021/04/12
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