Farewell

So, our dear friends. This blog is getting to the end of its life. But it has been a nice experience!

At the beginning of this assignment that was given to us, we took it like another work we had to do: we had deadlines to publish our posts and it was more of an obligation instead of pleasure. As time went by, we started enjoying it, discussing between the three of us ideas for the posts, helping each other, and in the end it took us little time to research information and come up with nice posts.

We’ve got a thorn twisedt in our side because we never got to go to Mutriku, to visit the power plant, as we promised our readers in the beginning. We are three in the group, and it wasn’t easy to coordinate, due to the big work load we have this semester.

As we are future engineers, and have an entrepreneurial mind, we have read about many projects, some theoretical, and some already patented and working. This serves us as motivation for the future. The three of us are studying what in  Spain is known as industrial engineering, and is a very general career. Therefore, we are all the time seeking for areas of the engineering world that thrive our interest, and energy generation from clean sources such as the sea, has certainly generated within us a huge interest. Bear in mind that we see the sea every day on our way to university and nearly every day of our life, and we’ve noticed the great potential that the sea has to generate energy.

To finish, we would like to thank our readers, that we hope have learnt as much as we have about different ways of obtaining energy from the sea.

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Dynamic Tidal Power

No. I’m not planning on talking about how much we all feel like being right now in summer vacation. Neither am I going to talk about beaches. Not even about the wonderful city we live in!

Just want you to take a good look at the photo. But don’t get too excited. Can you see the artificial breakwater that was built in the Zurriola beach in Donostia nearly two decades ago? Can you imagine it creating energy?

Well some Dutch engineers have come up with an idea: let’s build a long dam into the sea, make it form a T shape, and produce energy. This dam wouldn’t enclose an area, and it would benefit from the tide movement.

We all think about tides making the sea level go up and down, but in some places on earth, the tides run parallel to the coastline. Some countries such as China, Korea and the UK would be able to benefit from this, yet theoretical, energy conversion system.

One of the cons of this project is that it can’t be tested, or to be more precise, proper results would not be obtained. It is calculated that the generation capacity increases with the square of the distance of the dam. To make some simple numbers, comparing a 30 km dam with the one of the Zurriola (about 300m), the long one would produce ten thousand times more energy. So as you can see, it wouldn’t be useful to test it. That means investing millions of euros in a project that only works on paper…

But there are also more inconvenients. What would happen to shipping routes? How handle all the sediments that form around it? Remember that since the waterbreak was put in place in the Zurriola, the sand doen’t go away, making it a nice beach to hang out in. But this accumulation of mud, sand and other dirt in a generator like this can cause problems.

But not all of it is negative, because a single dam would be able to generate over 1GW. Bear in mind, that as Mikel mentioned in his last post, an operating undersea tidal stream generator has a capacity of 1,2MW, so we would be talking about eight hundred times more energy. What’s more, when we analyzed early on in our blog sea buoys, a single buoy was able to generate 150kW, nothing compared to what is estimated that this new technology could achieve.

So, even though it only exists on paper, it’s interesting to keep it in mind, because in a mid-long term it can become a viable project.

Publicado en Energía Mareomotriz | Deja un comentario

Saudi Arabia in Europe?

Following the line of previous posts in this one I write about another way of taking advantage of tidal power, by the method of Tidal Stream Generator.

First, we have to consider that the motion of a sea tide causes fast flowing volumes of water: Tidal streams. These can be used to obtain electric energy, with a similar technology to wind energy, taking into account that the sea water is slower and 800 times denser than air. So, it is possible to install underwater turbines to take advantage of tidal energy, by the system of Tidal Stream Generators, which converted the kinetic energy of the big masses of water in movement into electricity, as it is explained in this article.

There are different types of harness Tidal Streams, but the most powerful station that uses Tidal Stream Generators is SeaGen, in Nothern Ireland. This plant generates 1,2 MW for between 18 and 20 hours a day, enough to satisfy the demand of 1000 homes, thanks to a tower with two turbines. It has also got a system that makes the turbines work in both flow directions. The generator can go up for maintenance, too. The image below shows how it works.

This clean, renewable and predictable energy has got the positive points of Tidal barrages, but it’s also cheaper. The technology is similar to wind turbines and the affect to marine ecosystems and the visual impact are lower.

So, why a Saudi Arabia in Europe?

Saudi Arabia, as it is well known, is an Asian country which is the main exporter of oil in the world. However, there is a place in Europe that is also called Saudi Arabia, and not because it’s oil, but for its strong sea currents, with a speed of 30 km/h. This place is An Caol Arcach, also known in English as Pentland Firth, the strait that separates Orkney Islands from Scotland, in the island of Great Britain. According with this article, a tidal power station placed there can be capable of accommodating 10 GW of installed generating capacity.

In principle, a tidal energy company, Marine Current Turbines Ltd, has the intention to start working in Pentland Firth. The company wants to install 50MW of generating capacity by 2015, using SeaGen technology. If the local grid can take it, they have projects too for install up to 300MW or more by 2020.

So we can see that in Europe there are great possibilities to make use of sea power. In this post we have seen a way of develop this vast field, but there are indeed uncountable ways. Will, effort and investigation are vital if we want to have in our future a clean and reliable energy system. Now we just have to go for it.

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Tidal Barrages

As Jon mentioned on his previous post, there are three ways of generating electric energy from tides (one of them only works theoretically).

In today´s post, we are going to talk about the most common one: tidal barrages.  Usually they are placed on narrow bays or estuaries. The barrages use the difference of seawater level generated between their sides to generate electric power thanks to the motion of some turbines. A noticeable fact is that tidal power stations are only worth-building on those places where the difference between the high and low tide is at least of 5 meters. Those tidal power stations basically work as the ones we traditionally find in rivers: when the tide comes in, sluice gates are opened, so the water can flow into. When the accumulation of water reaches its maximum level, sluice gates close. The machine operators keep them that way until the low tide. This point is the optimum for energy conversion (maximum seawater level difference). Sluice gates are opened and the water flow makes the turbines move, which connected to some generators, produce the electricity.

Example: Rance’s power station (France). Remarkable facts:

–          Around its dam, apart from turbines and generators, there are also some rooms with extra machinery and control gadgets, where operators of the station work.

–          A total amount of 24 reversible turbines and 24 generators. The turbines reach 5700 revs per minute, achieving a maximum power of 240 MW.

–          The water flow is about 20 000 m³/s.

Let’s focus on the benefits and drawbacks of tidal barrages:

Positive points:

–          Clean and predictable energy source.

–           It is not oil dependent.

–          The dam can link up different cities and work as a new road for trains or traffic.

Among the drawbacks…

–          The tides and the electricity demand are not related, which is a problem due to the difficulties found in energy storage.

–          Ecosystems can easily be altered.

–          Introduction of difficulties in shipping.

On future posts, we will go on explaining the remaining methods: Tidal Stream Generators and Dynamic Tidal Power.

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Tidal power

Up till now, we have mainly talked about wave power, osmotic power and ocean thermal energy power. All of them consist in obtaining energy from the sea, be it by the power of the waves, the difference of salinity between two masses of water or by the difference of temperature of sea lever water and deep water.

Today a new concept is going to be introduced: Tidal Power. It is based on the movement of the rise and fall of sea levels. These tides are produced by the gravitational forces that the moon and the sun produce on the sea. Most places usually experiment two high tides and two low tides a day, although there are places that only have one high tide and one low tide a day.

Tidal power is not widely used yet, but it has certainly got a great potential.  On the one hand, the worst aspects are that the development is very expensive, and that like all marine power types, it cannot be take place anywhere. On the other hand, tides are a totally predictable phenomenon, therefore it makes it a totally reliable mean of energy. Bear in mind that the greater the tide differences are, or the stronger the currents are, more energy will be produced.

There are three main methods to generate power from tides, some of which will be studied in following posts: Tidal Barrages, Tidal Stream Generators and Dynamic Tidal Power.

Tidal Barrages make use of the potential energy of the tides. They are situated in river estuaries, and as the tide flows in and out, it generates power. But don’t be mistaken, it is not a dam, because it does lets the water flow in and out although it is not very nature friendly either.

Tidal Stream Generators are the classic machines that one thinks of when it is being talked about tidal power. They are like wind power generators, but placed under the sea. These generators take benefit of the kinetic energy of the water flows that tides generate to move an axis centered rotor. This is the cheapest way of generating energy from tides, so as the most environmental friendly.

Dynamic Tidal Power. It is a new way of exploiting the sea’s potential to create energy. It still hasn’t taken place anywhere, and is still under research.  It consists of a dam-like T form structure that comes 30 to 60 km out of the coastline. The idea is for it to interfere with coast parallel tidal flows, strong such as in China, Korea and the UK.  It would generate up to 1GW, but what would happen to shipping routes, marine ecology, sediments and so on?

 

If you want to read more about this, I recommend the wikipedia webpage, so as this other one.

 

 

 

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Eleven days in Cuba

In 1929 a yacht called ‘Jamaica’ travelled the whole length of the coast of Cuba. People that saw it could not know that thanks to the person who was in that yacht the first experiment about Ocean Thermal Energy Conversion took place.

Many times, we think that renewable energies are something new, even futuristic. However, some renewable energies, like OTEC, are known since a long time ago, and, what is more, they were investigated and applied with relative success in the first years of XX siècle. One person who did it was Georges Claude. In my last post I just wrote a line about him. Nevertheless, his great achievement deserves to be known and appreciated.

Georges Claude was a French scientific and engineer, disciple of Jacques-Arsène d’Arsonval, the first physician who theorized about the possibilities to exploit the Ocean Thermal Energy.

In 1926 Claude designed an open-cycle system to obtain electricity from Ocean Thermal Energy. In this system, as Jon wrote in his last post, seawater evaporates at low temperatures if it is in a vacuum. In Claude’s open-cycle, it evaporated at less than 27ºC.

After investigating the different characteristics of the water of the Cuban coastline, Georges Claude, together with his partner Paul Boucherot, decided Matanzas bay for his experiment. The depth was 700m. It started with the difficult collocation of a long tube to take the cold deep sea water. The final experiment was done on the 6th of October of 1930. He foresaw he could achieve 40 kW, and use 13 kW of them to pump the cold water. However, finally 22 kW were obtained, because the temperature difference was not as Claude initially expected. All in all, the experiment gave enough energy to illuminate 30 light bulbs (15 kW, approximately). Some people argued that an auxiliary motor was necessary for the activation of the plant, but we have to consider the incipient and experimental character of the investigation.

Georges Claude had many projects and continued investigating. He tried to open a power plant of 25000 kW in another place of Cuba to stimulate Cuban industry, even providing electricity to some southern states of the United States. However, the discovery of new oil wells diverted the attention from it. Also, eleven days after it started, a hurricane destroyed the OTEC plant of Matanzas. But the precedent was established…

There are three very interesting documents about this unknown event, which I have consulted:

One is the lecture that Georges Claude read the 9th October of 1930 in the Academy of Medical, Physical and Natural Sciences of Havana about the experiment (in Spanish).

The second one is an abstract about it (in Spanish).

The third one is a press article of the time (in English).

Experiments like that show us the history of renewable energies, the efforts made in its development and the long trajectory of obtaining electricity from the sea.

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Hybrid Cycle OTEC

After having explained two of the procedures to get electric power from ocean´s thermal gradient, you may be wondering… where is the need of a third one?

Well, the hybrid cycle combines the best characteristics of the previously shown processes (open cycle  & closed cycle), so that this third way is expected to be easily penetrable on the marketplace. Actually, it was conceived as a response of some marketing studies. However, it is to be yet tested and works just theoretically.

Hybrid cycles combine the drinkable water generation capabilities of open cycles with the potential for large electricity production capabilities offered by the closed cycles. Let´s explain how it works:

Warm sea water (which comes from the surface of the ocean) enters a vacuum chamber where it is flash-evaporated. After that, this steam arrives to a heat exchanger where it will play the role of a warm fluid and will be used to warm the working fluid, which works in a closed loop. Usually, ammonia is used as this working fluid (it has good transport properties, it´s easily available and, in addition, it is a low-cost fluid. The negative point is that it is toxic and flammable). Other options are fluorinated carbons, such as CFCs and HCFCs or hydrocarbons.

Observation: An interesting part of the process is that as water evaporates, it leaves all the impurities and salt, so the consequent steam is drinkable.

Once heated and evaporated, the working fluid vapor flows through a closed-cycle power loop. At this point, the ammonia is used to turn a turbine which connected to an electricity generator, supplies the customers with electric power. After that, the ammonia is condensed using cold sea water for it (from the deepest ocean waters). The non-condensables are then compressed and discharged to the atmosphere.

After this brief explanation (click here for further data ) we conclude that the role of seawater is double: on the one hand, it works as an intermediary heat transfer medium; on the other, we get potable water after the condensation process.

Negative points:

–          Drinkable water production and power generation are closely coupled. Changes or problems in either the water or power subsystem will compromise performance of the other.

–          Possible ammonia leaks could contaminate potable water obtained after condensation.

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