Tidal Energy

With the increasing use and high demand for switching to renewable energy sources to fulfill the world's total energy requirements, the use of different types of renewable energy sources has also increased. In today's time, scientists & researchers are looking for different types of renewable energy sources which can be used for generating renewable energy that can be further used for power & electricity generation. That's why many types of renewable energy sources are becoming popular in today's time.

The most popular renewable energy types are solar energy, wind energy, geothermal energy, biomass, and many others that contribute more than 50% of the total renewable energy consumed by the world. But apart from these common renewable energy types, many other renewable energy types are also becoming popular in today's time, such as wave power energy, tidal energy, hydropower, etc. In this list of renewable energy, tidal energy is emerging as one of the strongest renewable energy sources. In today's time, tidal energy is not widely used as a renewable energy source, but it has great potential for becoming a major renewable energy source for electricity & power generation. Tidal energy, a type of renewable energy source, is a pollution-free & more predictable renewable energy source than other major renewable energy sources. This article provides a complete description of Tidal energy, its future, advantages, and generation technologies. This article also provides insights into why tidal energy is still not used as the major renewable energy source despite its numerous advantages.

Introduction to Tidal Energy

Tidal energy, which is also known as a form of Hydropower energy, is actually the form of energy that is obtained from converting the ocean tides into useful forms of energy or power, mainly electricity. The tides in the ocean are the result of the gravitational force or attraction effect of the sun and the moon on the Earth's surface. This gravitational effect of the moon or the sun causes cyclic movement of the seas that results in the origin of the tides on the seashore. Since these tides are produced by the effect of the moon or sun's gravitational attraction towards the Earth's surface, they also have some forces which can be felt on the seashores. The force these tides have is used for the generation of tidal energy through multiple tidal energy generation methods. Since the gravitational attraction of the sun and the moon on the Earth's surface is constant, therefore tides are also constant throughout the year despite the weather or season. Therefore, the generation of or harnessing tidal energy makes it more predictable, which gives this energy form an edge over other renewable energy forms. This predictable nature of tidal energy makes it very special among all forms of renewable energy. Tidal energy is used for the production of many important forms of energy, but a major portion is covered in electricity generation.

Although tidal energy covers only a little portion of total renewable energy used in today's time, it has the potential to become the major contributor among the renewable energy sources for electricity generation and production of other forms of energy. Among all the renewable energy sources, the contribution of tidal energy is very less because of its high production and generation cost. The production cost for tidal energy is relatively very high than the production cost of any other form of renewable energy. Apart from the higher production and generation cost, the sites for the generation of tidal energy are also very limited, which results in the limited generation of tidal energy. The more limiting factors, including these two factors, will be studied in detail in the disadvantages part of this article.

Tidal Energy: History

Europe and the Atlantic Ocean region of North America were the first places used for the generation of Tidal energy. Historically, it can be seen that European & North American Atlantic regions were the dominant regions or major contributors in the total tidal energy production of the world. In the starting days of the tidal energy generation, the incoming water (tides) from the seas was contained in the large storage ponds, which forced the wheel to move. When the incoming water (tides) return back to the ocean, again, it forces the wheel in the ponds to move. This movement of the wheel generated mechanical energy that was used to produce mill grains. Many studies have found that tidal energy was first produced in Roman times or in the Middle Ages. It was only in the 19th century that the process of producing tidal energy (using spinning turbines and falling turbines) is used to create electricity. Electricity was first generated from tidal energy in the U.S. in the early 19th century. Later in the 2000s, electricity production from the tidal energy source increased significantly because of the predictable nature of tidal energy. Rance Tidal Power Station, which was built in France, was the world's first large-scale tidal energy generation power plant, and it became operational in the year 1966. This power plant was the largest tidal power generation power plant in terms of tidal energy generation until Sihwa Lake Tidal Power Station, which was built in South Korea, was opened in 2011. In today's time, the Sihwa Lake Tidal Power Station of South Korea is the largest tidal power generation plant in terms of energy outputs. This tidal energy power plant has a power generation capacity of 254 MW, and it uses sea wall defense barriers completed with 10 turbines.

Tidal Energy: Principle

The tidal energy is generated from the tidal forces of the oceanic tides, and these tidal forces result from the periodic variations in the gravitational force or attraction. This gravitational attraction is exerted by the celestial bodies of the Earth's surfaces. These gravitational force from the moon or the sun creates currents or corresponding motions in the Earth's oceans. Due to the rotational movement of the Earth, periodic changes in the sea levels have also been seen. But because of the consistent pattern of the Earth's rotational movement & the motion of the moon in Earth's orbit, these changes in the sea levels are highly predictable as well regular. The changing position of the sun and the moon according to the Earth's rotation is reflected by the magnitude and variations of the motion of the tides in the Earth's oceans. Other than this, the change in the magnitude and variations of the motion of the tides is also seen because of the geographical representation of the coastlines and the seafloors and the effect of the Earth's rotation.

Tidal power or energy generation techniques are the only technology that draws on the energy inherent according to the Earth's orbital characteristics. This is inherent mostly because of the Earth-moon system characteristics in the Earth's orbit, and to a lesser extent, because of the characteristics of the Earth-sun system. Whereas many other forms of natural energy (including both renewable & non-renewable forms of energy) such as solar power, wave energy, biofuel energy, wind energy, conventional hydroelectric energy, and fossil fuels are directly or indirectly exploited from the sun using many man-made technologies. A tidal generator is used for the generation of electricity by converting the energy produced from the oceanic tides. A tidal generator can yield maximum output when higher tidal current velocities and greater tidal variations are seen in the tides. Therefore, the potential of the tidal electricity generation sites can vary according to the tidal current velocities and tidal variations at the sites.

Tidal energy is a renewable energy source because the oceanic tides are practically inexhaustible. This is because of the gravitational attraction of the Earth with the moon or the sun, and the rotation of Earth or the moon is practically never-ending. The movement of the tidal energy or the production of the electricity from the tidal energy results in the loss of mechanical energy in the Earth-moon system. This is because of the consequent viscous dissipation in turbulence and at the seabed and pumping of the water through natural restrictions around coastlines. It is interesting to note that this loss of mechanical energy in the Earth-moon system has also caused the slowing down of the rotational movement of the Earth in its orbit in the 4.5 billion years.

During the period of 620 million years (which is the period of the rotation of the Earth around its orbit since it has formed), the Earth-moon system has lost about 17% of its total rotational energy, which has resulted in the increased day length on the Earth from 21.9 hours to 24 hours (present single-day time on Earth). While it can be said that the tidal energy harnessed is taking additional energy from the earth-moon system and affecting the movement of the Earth, the actual effect on daily life is negligible and would not be noticeable in the foreseeable future.

Tidal Energy: Generation Methods

There are multiple methods for the generation of tidal energy or power, but not all of them are effective and used on a large scale. Therefore, all methods of tidal power generation from the tides are not described, but only the most famous ones among them are explained. These famous methods of tidal power generation are currently in use on a large scale, and each of these methods has its advantages & limitations. Following is the detailed description or explanation of the methods that are used on a large scale for the production of tidal energy:

1) Tidal Lagoon

This is a newly designed model for the production of tidal energy in which circular retaining walls that are embedded with turbines will be constructed, and this will help to catch the potential energy of the tides. The location of the created reservoirs in this generation method is artificial and does not require a pre-existing ecosystem for capturing the potential energy of tides. The lagoons used in this generation method are also present in double or triple formats with or without pumping reservoirs. These pumping reservoirs help to flatten out the power output in the lagoons. The pumping power required to flatten out the power output could be provided in excess by the renewable energy power grids such as solar photovoltaic arrays, wind turbines, and many others to fulfill the demand of power supply. When this renewable energy is provided in excess in the lagoons, it could be used and stored for a later period of time rather than being curtailed. Tidal lagoons that have a time delay between peak production and are geographically dispersed would also flatten out the peak production.

2) Tidal Barrage

The tidal barrage is based on the principle of using the potential energy according to the differences between the heights of high & low tides (also known as hydraulic heads). Through the strategic placement of specialized dams, the potential energy from a tide is seized while using tidal barrages to generate tidal power. Whenever there is a temporary increase in the tidal power due to the rise in sea levels and larger tides come in, the increased tidal energy is channeled into a large basin (situated behind the dam), thus, holding a large amount of potential energy from tides. When the intensity of the tides starts receding, the stored potential energy into the basin is converted into mechanical energy, and at the same time, water is released through the large turbines. When the water is released through these turbines, electric power is generated with the use of generators.

3) Tidal Steam Generator

Tidal stream generators work on a similar principle in which power is generated through wind turbines. The reserved water collected from the oceanic tides is released from the turbines where the generator is connected and uses the kinetic energy collected from the turbines for electricity generation. These tidal steam generators can be constructed with the existing bridges or can be entirely submersed at the tidal power generation sites, thus, reducing the concerns or hazards related to the impact of these generators on the natural landscape. At some specific sites, high velocities are created because of land constrictions like inlets or straits, and power generated because of these high velocities is captured with the use of turbines.

Tidal Energy: Advantages & Benefits

Tidal energy has the potential to become a renewable energy source that can replace the dependency of the world on fossil fuels for fulfilling the energy requirements. Tidal energy can fulfill the world's total energy requirements in the foreseeable future as fossil fuels, and other non-renewable energy sources are going to end in the next 30--40 years. Like many other renewable energy sources, tidal energy has very less or no hazardous impacts on the environment, and the natural landscape makes it even more special. Following are the advantages of using tidal energy as the energy source for fulfilling the energy requirements of the world:

1) The predictable nature of tides:

The oceanic tides are the result of the gravitational force or attraction effect of the sun and the moon on the Earth's surface. Since the gravitational attraction of the sun and the moon on the Earth's surface is constant, therefore tides are also constant throughout the year despite the weather or season. Therefore, the generation of or harnessing tidal energy makes it more predictable, which gives this energy form an edge over other renewable energy forms. This predictable nature of tidal energy makes it very special among all forms of renewable energy.

2) Everlasting Fuel supply:

Tidal energy is a sustainable, carbon-free, and renewable source of energy. This energy source is sustainable and renewable because the Earth will have oceanic tides for billions of years. The tidal energy source is called a renewable energy source only because of its everlasting nature, and that's why it can be said that this energy source is a type of fuel supply that never runs out. And, in today's time, the world is looking for only such fuel supply or energy sources that are everlasting and don't have to depend on multiple energy sources to meet its energy requirements. Therefore, if technologies and techniques are developed for harnessing tidal energy, it can fulfill all the future needs of the total world's energy.

3) Impact on Environment:

The use of tidal energy does not produce any greenhouse gases, and therefore, the use of this energy source is not only safer for mankind but also protects the environment.

4) A promising source for future energy supply:

In the current situation, there are some hurdles and serious challenges related to tidal energy generation and production that need to be worked out, but with the advancement of technology and improvisation in harnessing techniques, tidal energy has been the promising future energy source for a very long time. As the research and development in the tidal energy field are progressing, there are very good chances that many technologies will be developed to harness tidal energy with lower costs.

These are some major advantages of using tidal energy over other renewable and non-renewable energy sources to fulfill the world's total energy requirements. Some of these advantages also suggest why in the future, tidal energy is preferred over all other renewable energy sources, such as the same efficiency in all seasons, no emission of greenhouse gases, predictable nature of oceanic tides, and many others.