Importance of Natural Resources

OceanMOOC | 10.5 | Sustainable Energy from the Ocean


So welcome. We’re going to look at solutions
how the ocean can contribute to the generation of renewable energy into the future. Today
the renewable energy’s share for electricity is about 22% and it’s growing to 26% by
2020. However, if you look at new energy systems coming online, about half of that is already
from renewables and what I found the most interesting, it’s actually China who is
the biggest force where 40% of the global renewable energy is produced today in China.
The need for global electricity is in 2012 about 2.5 terawatts and it could almost double
to rise to 4 terawatts by 2040. Ocean energy on the other hand provides at best about .4
terawatts which could be one…about 10% of the global energy need into the future. Today
energy out of the ocean is only a small fraction, but it’s a fast growing area. So how then
can ocean energy be produced? Electricity from the ocean that is.
So there’s five different ways how we can do it. On the one hand we can use the tidal
elevation that we see in the oceans and to turn that into energy. We can use ocean currents,
waves and swell. But we can also use the difference between the warm and the cold temperature
of the ocean and also the salinity gradients between fresh water on land and ocean water.
So the energy in the ocean waves is a form of solar energy that is mediated through the
wind system and the waves into the atmosphere. The energy of the ocean tides is provided
by the gravitational acceleration and the difference between the sun and the moon and
the planet as they have different constellations. And the energy from ocean currents obviously
comes directly from the temperature difference and the winds. So all of them have their roots
in the natural environmental system and are sustainable, free of CO2 and could run forever.
So now to look at some of the more specifics, how energy can be produced. Let’s start
with the tides. We have tidal ranges that go up and down twice a day in many parts of
the world. And in some regions the tidal difference is very large. In some are low for example
we find ten meters or thirty feet of tidal difference between high and low water and,
and it’s even more in the Bay of Fundy. Those places have understood how to use the
power of alternating sea levels and use that difference of gravity to fuel turbines that
can produce electric energy from the tidal difference.
At the same time you can also have tidal currents that go back and forth every six hours in
a different direction and use tidal turbines to harness that energy. It is estimated that
together tidal currents and tidal turbines can produce as much as .9 terawatts which
would be quite a significant fraction of the global energy production. But these systems
are not yet fully installed but we see a lot of potential growth that comes our way into
the future. Today in the tidal turbine systems we have
twin systems and this company called Seagen, they are producing these twin systems. They’re
lowered into the tidal streams and then they slosh back and forth when the currents go
back and forth. And this electricity is really useful for small communities near tidal outlets,
but they’re also already been installed in Pacific islands, in atoll systems where
you have tidal currents sloshing back and forth. So I think it’s a wonderful distributed
form of new energy that we can see in the future.
The other methods that we can use to generate electricity from the ocean comes from a different
system. And here we’re harnessing the waves. So the ocean has a lot of surface waves that
go up and down. And what we can devise is different systems that take advantage of being
thrown up and down with the ocean currents and release that kinetic energy and turn it
into electricity. Some use systems where the waves spill over an artificial reef and then
slowly the water as it sinks down generates energy. Other systems use mechanical elements
that they get pumped up and down to produce energy that way.
Those stations are not very big right now. They have maybe 75 or a 100 kilowatts which
is a kind of small production. It’s technically quite challenging because you’re in the
middle of the ocean where the waves are sloshing back and forth. Maintenance is not so easy.
But it’s it is estimated that this will become an increasing possibility to generate
energy in those places of the world where waves are abundant. The problem with waves
also is they’re not always there. In some seasons the waves are abundant, in other seasons
the ocean is more calm. So they’re not that stable of an energy source compared to the
tides. The third way you can do energy from the ocean
is you can harness the power of the great ocean currents. We know about the Gulf Stream
and deep ocean circulations. We know about coastal currents and all of these provide
energy that we could also harness. And there are different systems designed that look like
giant kites with propellers underneath them that will then sail in the Gulf Stream and
sail in the major ocean currents, have rotors that spin around and generate currents. These
currents would then be transmitted through the kites. But you can also see you have the
energy in the middle of the ocean, transporting on land is a bit of a challenge because you
need to have plugs where you plug these turbines in and then you have to have the cables that
bring the energy back to shore. Strong currents we find on the western side
of ocean basins. So for example, in front of major cities like New York or Washington
D.C. this would be an option. But on the eastern ocean basins the currents are usually rather
weak so cities (places) like Cape Town or Morocco couldn’t benefit from that. But it’s another area
that people are looking into. Some more exotic areas to produce energy come
from ocean thermal energy. Here the idea is to use the difference between the warm surface
and the cold deep waters. So you’re basically setting up like a heating system where you
pump up some of that cold water and bring it together with the warmer water from the
surface, and from that temperature gradient you use special substances that evaporate
at low temperatures, that drives then generators and then they get evaporated and cooled down
with the ocean cold temperatures. But because the temperature difference between the warm
and the cold is not very big, it’s maybe 10-15, maximum 20 degrees Celsius, these systems
are not very efficient, so you need a lot of water to pump that.
On the other hand, not everywhere on the planet we have access to cold ocean waters. The country
where I live in Germany, there is no deep ocean in front of our country, but other islands
like Hawaii, they are located in the warm tropics and have cold waters in deep places.
So they are very well suited. You can calculate that this thermal energy can produce about
two times or even three times the energy needed to provide the whole world with electricity.
But then what you would have to do, you would have to harness all the warm and cold temperature
differences of the ocean. That is not desirable, because you would change the ocean stratification,
you would change the ocean circulation. So maybe 10% is maybe the maximum that you want
to harness. And if you do that, it’s going to be a contribution at maybe the 5% or 10%
level to global energy production. Maybe the most exotic way to produce energy
out of the ocean is from the difference between fresh water and salty water. Here you are
harnessing the osmosis, that is the primary ability of a particular class or a particular
substance that you bring between salty and fresh water and then the fresh water by osmosis
goes through that membrane and builds up a pressure. From that pressure difference between
fresh and salty water again, you can drive a turbine and you can generate energy with
that. It’ll take quite a bit of water to do it,
but it has been tried and it’s a, it’s a possibility to use that technology not only
to produce energy, but also to produce purified seawater which then becomes fresh water to
alleviate some of the challenge that we have around water security. The efficiency of these
systems is probably not so high. And there’s only a few places on the globe where this
will be…could be done at a big scale. It requires a stable infrastructure, there’s
somewhat of a high maintenance needed. But I think we’ll see it in many areas around
big settlements that these combined osmosis energy production and water purification will
be part of the solution that we can use the energy for.
So if you think of the ocean and its contribution to energy, there’s a number of great potentials
out there. I think it’s a space where innovation is happening. We’re seeing an enormous amount
of projects being started, looked at around the world. And the prospect that we can generate
about 10% of electricity from oceans, sustainable energy without producing CO2, without harming
the environment is very exciting and I encourage you all to engage in this thinking, in this
technology and develop new ways so we can harness the power of the ocean for sustainable
ocean development.


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