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
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