Name: Can Underwater Turbines Solve Our Energy Problems?
Uploaded: 2021-04-12T09:41:57.000Z
Duration: 14 min 24 s
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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?

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

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

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

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

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 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

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

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Can Underwater Turbines Solve Our Energy Problems?

incredibly

massive

significant

evidence