Prof. Altaş: The current outlook of wave energy is similar to the outlook of solar energy 20-30 years ago

What is wave and tidal energy and how does it work?

Renewable energy sources have emerged as an alternative due to the limited availability of fossil fuel-based energy sources and their negative environmental impacts. While the installation and utilization of renewable energy sources based on wind and solar radiation has increased rapidly in the last decade, the installation of wave and tidal energy, another renewable energy source, has remained quite slow. We will discuss the reasons for this a little later.

Wave energy is the energy generated by the movement of sea or ocean waters with the effect of wind. A kinetic energy occurs as the water rises and falls, that is, fluctuates. This energy is captured by apparatus with linear or rotary motion and converted into electrical energy. However, the heights and frequency of waves are not constant. In other words, the natural formation of waves is irregular. Sometimes the height of the wave is high and sometimes low, while the height and frequency of fall are also variable. This irregularity is also reflected in the electrical energy produced and irregularities occur in the voltage amplitude, frequency and power produced. To overcome this, it is necessary to use mechanical and electronic regulators. Of course, such additional apparatus increases installation costs.

The tidal phenomenon is slightly different. The tide is an event that occurs when the moon moves closer to some parts of the earth and further away from others. The waters on the side of the Earth close to the moon rise while the waters on the side far from the moon fall. The rising tidal waters can be transferred to a reservoir, and the kinetic energy generated by the falling tide can be converted into electrical energy, just like the use of water in a reservoir. I saw this tidal phenomenon in 1988 in the Bay of Fundy in New Brunswick, Canada. 

 I went to the Bay of Fundy around 10:00 a.m. and walked along the shore, and when I got back around 3:00 p.m. I saw that the shore was filled with water. The water level was continuing to rise. In fact, the level of water rise can be easily understood from the rocks in the photograph. In later years, I read that a hydroelectric power plant was used as a reservoir to hold the rising water as a result of this tide. As in hydroelectric power plants, the accumulated water is regularly lowered and converted into electrical energy by hydraulic turbine-generator units. By controlling the water fall, a more regular electrical power and energy is obtained, unlike wave energy. 

What is the wave and tidal energy potential in a geography like Türkiye? 

There are no tidal events in Türkiye at a level to generate energy. The most suitable places for electricity generation from wave energy are the Aegean Region, Marmara Region and Western Black Sea coasts. In fact, wave energy potential and wind energy potential are parallel to each other. However, since the size of the sea surface increases the pressure to be formed, it also increases the energy potential.

The coastal length of our country, which is surrounded by seas on three sides, is approximately 8210 km. However, Türkiye’s wave potential is not suitable for installing even small wave energy systems in every coastal area. Approximately one fifth of Türkiye’s total coastal length has a wave energy technical potential of 18.5 TWhour/year (approximately 2.11 GW). According to some studies, the wave energy potential of Türkiye is approximately 10 TWhour/year as a usable resource in the wave power range of 4-17 kW/m (m: wave crest length). 

The north of the Bosphorus, the western Black Sea region and the southwest coast of the Aegean Sea (between Marmaris and Finike) have been suggested as the best locations for wave energy. In several scientific studies investigating the wave energy potential of the Black Sea region, the southwest coast of the Black Sea has been suggested as the best location for the establishment of a wave farm. The annual average wave energy resource of the western parts of the Black Sea (especially in the southwest) is up to 3 kW/m. The largest average wave power in the south-western part of the Black Sea is about 7 kW/m and the average wave power in the eastern part is about 3 kW/m. Sinop has the highest value with a wave power flux of 10 MWh/m. The annual wave energy potential of the other coastal provinces (Samsun, Ordu, Giresun, Trabzon, Rize and Hopa) is about 6 MWh/m, which is generated by waves with significant wave heights of 0.5-2 m and wave periods of 2-5 s. The wave energy potential of the southeastern coasts of the Black Sea is estimated to be low.

What are the advantages and disadvantages of wave and tidal energy compared to other renewable energy sources?

Wind and solar energy are the most widely used renewable energy sources. Compared to waves and tides, they are easier to install and maintain, have lower installation costs, and are easier to control the electrical power generated. There are also discontinuities in wind speed and daylight intensity. However, these discontinuities are not as fast and sudden as in wave energy. The rate of change of solar radiation is slow during the day, if not at night. This makes it easier to control and stabilize the electricity generated from solar energy. The periods between the tides in wave motion can sometimes be shorter and sometimes longer, as shown in Figure 2, and the wave height is not the same. Even if we assume that the wave heights are the same, the different durations between the tides create an irregularity. While electrical energy can be generated when the wave is high enough, it cannot be generated when the wave dies out. In order to get a regular and stable electrical power, this gap must be filled with mechanical or electronic regulators. Otherwise, the change of voltage to be generated from irregular waves will be irregular as shown in Figure 3. There are methods that can be applied for this. However, it should not be forgotten that each apparatus added increases the cost of the system. 

Installing offshore is much more challenging than onshore wind and PV solar installations. This difficulty applies to both onshore and offshore installations. The wave energy system to be installed must be able to withstand unexpectedly high waves that occur at unexpected moments. In addition, transportation of the generated electricity to the shore is another operational challenge. Onshore wind and solar PV systems have fewer installation, operation and maintenance challenges.

 How are wave and tidal power plants built and what technologies are used? 

It is useful to clarify the concepts of wave and tide. Because waves are also formed by the movement of sea or ocean water coming and going. However, while the average water level remains the same in wave phenomena, in tidal phenomena the water level generally rises and falls. There may be no tidal fluctuations. Depending on the distance of the Moon from the Earth, the sea water level rises and falls collectively. For this reason, the rising water during the tide is collected in a basin and the water discharged from this basin during low tide is converted into rotary motion and then into electrical energy by hydraulic turbines, just like in a reservoir. 

Installations to generate electricity from waves can be located either onshore or offshore. In general, buoy-type and oscillating wave chamber (OWC) type structures capture the changing motion of the wave and convert it into electrical energy by transferring its linear or rotary motion to generators with mechanical converters. In buoy-type structures, the vertical motion caused by the rise and fall of seawater is captured and converted into energy, while in oscillating wave chambers, the air flow caused by the rise and fall of seawater is compressed in a closed cell and the turbine is rotated by the air pressure generated, similar to wind turbines. 

In principle, there are wave energy converters with different names that use these two methods. 

As I mentioned in the previous sections, the biggest problem of wave energy systems is their installation, operation and maintenance. An installed system must withstand unexpected dangerous waves and not collapse. In addition, it is possible to experience both operational and environmental problems in the transportation of electricity generated in offshore installations to the shore with undersea cables. Although offshore energy potential is higher, shore-based installations seem to be more advantageous in terms of operation.

What are the environmental impacts of wave and tidal energy? 

Wave and tidal movements are environmentally friendly sources of energy production. Since they do not use fossil fuels, they do not release toxic gases into the air. In systems based on tidal movement, if the area required to store the rising water is on land, it may have a small dam lake effect. If the storage area is built by installing a platform in the sea, it may have effects on sea creatures and sea transportation as well as visual pollution. However, there is no toxic gas emission.

Offshore and onshore wave energy conversion systems may only have effects such as visual pollution and slightly restricting the habitats of marine species. Although the construction of shore-based oscillating wave chambers or cells embedded in other structures on the coast eliminates visual pollution, these structures may not always be possible. In short, wave and tidal energy is clean energy. There is no toxic gas emission. The only negative environmental impacts are the image they create on the sea surface, the slight restriction on maritime transportation and the slight impact on the habitats of sea creatures. Of course, one of the problems is that the used structure becomes idle after a certain period of time. However, the idle structure can be recovered through recycling.

What is the cost and economic return of wave and tidal energy? 

Wave and tidal energy conversion systems have higher installation and operating costs than wind and PV solar energy systems in today’s conditions. Installation costs are quite high due to the difficult working conditions at sea. In addition, the difficulties of building a durable structure also increase this cost. The maintenance costs of wave and tidal installations will inevitably be higher than land-based systems. In addition, making the irregular voltage variations produced usable also requires additional costs. Due to the high salt content of sea water, metal components used in wave and tidal installations are subject to rapid corrosion. Therefore, it is necessary to use materials that are resistant to sea water and do not rust immediately. This means an increase in cost.

Once a successful installation is made and energy production starts, the system is expected to amortize the installation costs. Since wave and tidal movements are natural and free, the input energy will be natural and free. However, since the installation costs are higher than wind and PV solar energy systems, the amortization period will be longer.

What is expected in the future for wave and tidal energy technologies? 

In our country, which is surrounded by seas on three sides, there is a remarkable wave energy potential especially in the Western Black Sea and the Aegean Sea. Although it is an inland sea, there is also potential in the Marmara Sea. For small-scale installations, the Central and Eastern Black Sea Sections east of Sinop are also candidates for evaluation. New wave energy technologies are needed to reduce the cost and make it competitive with other renewable energy sources. These technologies are aimed at developing more efficient and useful turbines, as well as power electronic converters that will enable load and grid integration. This is the case not only for Türkiye but for all wave energy conversion systems in the world.  The United States National Renewable Energy Laboratory (NREL) has initiated four new projects related to wave energy conversion systems. These are;

1. xWave

2. StingRAY

3. Floating Oscillating 

Water Column

4. Floating Oscillating 

Surge Wave Energy Converter

It is given as xWave has a remote controllable structure. It can generate 45 kW of power. When high and dangerous waves arrive, it automatically retracts itself below the surface of the sea and when the danger passes, it can resurface under remote control. String RAY has been developed to provide energy to near shore and isolated islands. It can generate around 50 kW of power. Protoip production and tests are ongoing. The Floating Oscillating Water Column (FOWC) is a floating version of the classic OWC technology. As waves enter and exit the open chamber of the device, the water passes air through a turbine to generate electricity. It can be controlled remotely. Work is ongoing to increase the capacity and efficiency of the device. The Floating Oscillating Wave Energy Converter (FOSWEC) is a biplane floating oscillating wave energy converter that can be deployed at any water depth. Capable of generating up to 100 kW of power, this device is currently undergoing control studies to increase its efficiency depending on the wave conditions.

As can be seen, studies on wave energy continue in areas such as durability, efficiency increase, maximum power increase, remote access, developing flexible control algorithms, and providing easy load and grid integration.

What can you say about the future of the wave and tidal energy sector in Türkiye? 

Since there are no tidal events in Türkiye, there has not been any investment or initiative in this field. However, studies on wave energy are carried out in universities. Real wave energy applications are generally at the prototype level. One of them was realized in the Karasu district of Sakarya with the project titled “Electricity Generation from Wave Energy” launched on February 15, 2008 in cooperation with the National Boron Research Institute (BOREN) and Turkish Electromechanical Industry Inc. The 5 kW power and mobile system consists of 4 pontoons, buoys and a generator. Apart from this, although small applications and trials have been carried out, there is not yet a significant wave energy installation with energy production in our country. There were some entrepreneurs who contacted me, but we only had a preliminary meeting and nothing more. We had started to install a 2 kW wave energy system at the back of Trabzon Port. We were installing it 30 m off the shore. It was going to be a kind of Wave Energy Research Laboratory. However, when about 80% of the mechanical parts had been assembled, unfortunately, the installation was knocked down by 5-6 m high waves at night. We pulled the material out of the sea, but we could not re-install it because there was no budget to re-install it. We could not find additional budget. I know how sad it is, but it just stayed like that. 

How important a role can wave and tidal energy play in meeting global energy needs? 

The areas richest in wave energy on Earth are between latitudes 40o-60o in both the Northern and Southern hemispheres. However, the area with the highest annual average potential is between 40o-60o latitudes in the Southern hemisphere. The net wave power (excluding areas less than 5kW/m and glaciers) of some of the wave energy-rich regions is given in 

The wave powers of some countries are as follows: Ireland 21 GW, Portugal 10 GW, Denmark 3.4 GW, Sweden 1.0 GW, England 120 GW and on the Mediterranean side, France, Italy, Spain and Greece have a total wave power of 30 GW. Approximately one fifth of Türkiye’s total coastal length has a wave energy technical potential of 2.11GW. 

What advice would you give to young researchers working in this field? 

The current outlook of wave energy is similar to the outlook of solar energy 20-30 years ago. If progress is made in areas such as easy installation, durability, efficiency increase, maximum power monitoring, remote access, development of flexible control algorithms, easy load and grid connection, wave energy systems will become better over time. My advice to young researchers is to conduct research on these topics and contribute to progress. There is a lot to be done.

What is the most common misconception about wave and tidal energy? 

Wave energy conversion systems are initially perceived as a very easy, ready-to-use type of energy. However, the wave itself is raw. It needs to be cooked and baked. It is not enough to put a buoy on the sea surface or to compress air in a wave water cell. As with all mobile electricity generation systems, wave energy must be captured by a turbine and transferred to the generator. Various turbine structures are available to capture wave energy. Studies on more effective and efficient turbines are ongoing. Our young researchers should know that there are 2 parts in wave energy conversion systems. These are mechanical and electrical parts. First, the wave energy needs to be captured, then processed and made usable. The electrical part requires a generator, as well as power electronic converters, regulating filters and energy storages, even for a short time, to eliminate the energy interruption caused by wave irregularity.

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