We owe the basic physical finding that all things with mass gravitate towards one another to Sir Isaac Newton. He discovered the force of gravity by watching an apple fall down.
Today we know that gravity has a significant influence on our environment and on our life on earth. One phenomenon caused by this elementary power is the recurring rise and fall of the sea level. Low tide and high tide result from the gravity of the moon, the sun, and the earth. And this power has to be immense in order to be able to move the water of entire oceans – so why not try to benefit from it, for example, to generate energy?!
It has always been like this. Centuries ago, people living at the European coasts already noticed that they could use the ever-recurring power of the tide for their purposes. They built so-called tidal mills, the precursors of tidal plants.
Today’s tidal plants of conventional build function according to the same principle as the tidal mills. They consist of a dam constraining the water of the tide. Turbines within the dam are driven by the stream of water entering or leaving the dam and thus generate electric power. The output of such a conventional tidal plant greatly depends on the tidal range, the number of turbines and the volume of dammed water. There are only a few places on earth that offer ideal geographic conditions for economically operating a tidal plant.
The most famous example is the tidal plant in St. Malo at the French Atlantic coast where the usual tidal range is 12 meters. The plant generates about 600 GWh per year, which corresponds to 0.2% of the demand for electricity in France. The dam required for such a plant always affects the environmental conditions of the coastal region in question, often with a strong impact on its flora and fauna. Therefore, tidal plants are always an ecological issue
The latest generation of tidal plants
The homepage of FIZ Karlsruhe‘s BINE Information Service provides short, concise, and practice-oriented information on current developments in energy research. There is an interesting description of a prototype from the latest generation of tidal plants. Its design rather resembles an underwater wind park. There are no more dams but the turbines are located directly within the tidal stream. These underwater turbines are low-maintenance and easy to install.
The investment and operating costs are significantly lower than with traditional tidal plants. A pilot plant is being built near the Canadian coast in the Bay of Fundy and will be put into full operation in 2017.
The technical core of the plant consists of the newly developed turbines. They are mounted to platforms on the bottom of the sea and automatically align themselves with the sea current. At the same time the water cools the generators of the turbines. These lightweight and robust turbines were developed by Schottel Hydro. They are attached to water-filled bodies and are practically floating underwater while in operation. The bodies can be emptied for maintenance. The uplift then lets them rise to the surface together with the turbines.
Fig. 1: Drawing from patent DE102012106099 (filed in 2012) showing an underwater turbine by Schottel. At first glance, it looks just like a wind turbine
But who is the company Schottel Hydro that has significantly contributed to the development of the latest generation of tidal plants? Schottel Hydro belongs to the Schottel group whose main area of business, according to their website, are drives and steering systems for ships. And indeed it is just a small mental step from a ship’s propelling screw to that of a water turbine. Some of the know-how and expertise can be transferred: a clear competitive advantage.
A patent search on STN sheds more light on the market environment
A search in the patent file Derwent World Patent Index® (DWPISM) reveals other interesting details. Each patent filed is considered a clear sign of technical progress and innovation. Patents reflect a company’s interest to gain or maintain a foothold in the market. Our search was carried out on the new STN platform. STN offers powerful analysis functions providing a meaningful insight into the developments in this sector. Just a few analysis steps suffice to generate market-relevant information. It is always important to know one’s competitors and to assess their strength on the market.
Our search revealed that the Schottel group has entered the market for renewable energies just a few years ago, as a lateral entrant from a different field of technology. A first patent for the newly designed turbine for tidal plants was filed in 2010, others followed in 2011 and 2011. An analysis of the Schottel patents shows that in earlier years, Schottel had only filed patents for drives and steering technology of ships. But a statistic analysis of all patents filed from 2004 to the present also shows that there is no real “top dog” yet, i.e., up to now, no company has filed significantly more patents than the others.
The strongest competitors so far are the German technology group Voith, Tidal Generation Ltd (taken over by Alstom in 2013), Openhydro IP Ltd and Dalian University in China. All in all, the number of patents filed has continuously increased over the last ten years, which means there is a growing market for this technology.
Fig. 2: International patent applications (PY.B) for tidal plants from 2004 to 2013. The black trend line shows that their number is strongly growing (the figures from 2014 were not considered, as they are not yet significant)
However, tidal plants still lead a niche existence compared to other renewable sources of energy. There are several pilot plants in operation to find out whether it will be possible to generate electricity with this technology to an increasing extent in the future. The market is still in an experimental stage and more research is required to optimize the technology.
It remains to be seen whether Schottel Hydro will be able to establish itself on the relatively new market for tidal plants. Much will depend on whether the pilot plant near the Canadian coast will stand the test and prove to be profitable.
Pelamis (“the sea-snake“) - a wave power plant
Besides the tidal plants, there are other areas of research dealing with maritime sources of energy. Wave power plants generate electricity from the movement of the waves. There are already some pilot plants using this technology in operation.
One type of wave power plant is the “sea-snake” or Pelamis (Greek for sea-snake). This plant has a flexible, snake-like design and floats on the water. Pelamis is 180 m long and consists of several metal cylinders connected by flexible couplings. The “sea-snake” is fastened to the bottom of the sea by cables and aligns itself at a right angle with the wave crests.
The recent history of Pelamis Wave Power Ltd, the inventor of the sea-snake, shows how difficult it is to survive on a new technology market. At the end of 2014, the company went into administration. In spite of the promising pilot plants near the Scottish coast there had not been enough investors to continue research and development.
The drawing below is taken from patent WO2011061546 of the company Pelamis Wave Power Ltd. It shows the core part of the wave power plant, the joint between the cylindrical buoyant elements. This is where the energy is generated from the movement of the waves.
Fig. 3: Drawing from patent WO2011061546
Description from patent WO2011061546
Obviously, the rough Scottish sea inspires the inventors of wave power plants. Another pilot wave power plant named Limpet already supplies electricity to the small Scottish island Islay. It sits on the coast just like a limpet.
Limpet consists of a concrete chamber that opens to the sea below sea level. The waves lift an air column within the chamber. When the water falls, the air is sucked back. This to and fro of the air resembles to the breathing of a lung. The powerful flow of air drives a turbine that generates the electricity. But in fact the plant also generates a loud “breathing sound”. The technology is also referred to as “oscillating water column“ (owc).
Fig. 4: Drawing from patent GB2250321 filed in 1992 by the inventor Alan Wells. It shows the functioning of the wave power plant Limpet
Researchers indeed need a lot of patience before their inventions are optimized for application in continuous, profitable operation. The basic patent for the Limpet was published in 1992; in 2001 the pilot plant was put into operation. In the meantime, this technology has become so interesting that the company Voith has also started using it and has been filing patents for it since 2008.
An intelligent combination of technologies
The icing on the cake regarding innovation is an intelligent combination of two technologies. The idea is to generate renewable energy directly where it is needed. This avoids the problem of energy transport and the loss of energy that comes with it. In our case, the energy generated from the sea is used by seawater desalination plants working with reversed osmosis. Since these plants require high pressures of 60-80 bar it makes sense from an economical point of view to connect them directly to a wave power plant. Patent WO 2014100674 describes such a combination. In this case, the energy of the waves is directly transformed into mechanical energy in order to generate the necessary pressure.
All plants described above have been designed to use the enormous power of the oceans as a renewable source of energy. The different technologies compete with each other. It is yet uncertain, which of them will prevail and be widely used in the future. And there are constant drawbacks: Winter storms and the aggressive salt water impair the technical parts, or the energy output is not always sufficient. But in any case the additional research effort will pay off. Experts estimate that about 15 % of the global demand for electricity could be satisfied by using marine energy.
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