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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
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