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Tidal Energy Definition

Sihwa Lake Tidal Power Station

The oceans on our planet have a great potential to generate clean electricity using the tides that occur two times a day and are generated by the gravitational forces of the Moon, Sun and Earth combined.

What is Tidal Energy? – Definition

Tidal energy or tidal power is a form of alternative energy that is also renewable because the tides in the planetary ocean are produced with extreme regularity every day by the combined gravitational forces of the Sun, Moon and our own planet.

To generate electricity using the kinetic energy of the tides, mankind has created underwater turbines that look almost similar like wind turbines, but they are smaller and more robust.

Power is generated by turning the kinetic energy of the moving water into mechanical energy (the underwater turbine that spins under the action of the tides) that is then turned into electricity by a powerful generator.

How Does a Tidal Power Plant Work?

Tidal power plants work by generating clean electricity using the movement of the water created by the tides.

Tides on planet Earth are caused by the combined gravitational forces of the Moon and Sun and the rotation of our own planet.

Tidal power plants are only installed across coastlines because these areas that are closer to the shore, experience two high tides and two low tides every day.

Current tidal technology, requires that the difference in water levels between the low tide and the high tide must be at least 16.4 feet (5 meters) to be suited for tidal power production.

Technology Used Today By Tidal Power Stations

Mankind uses today three different technologies to turn the kinetic energy of the tides into clean electricity.

1. Tidal Barrages

This type of tidal power plant is considered one of the most efficient technologies created for tidal power production because it relies on a dam that utilizes the potential energy produced by the change in height between high and low tides.

The difference in height between the high and the low tide is used to turn a turbine or to compress air and generate electricity in both cases.

At low tide, the water stored in the reservoir flows out into the sea and spins the turbines to generate electricity.

Tidal barrages have a few benefits because they use a dam-like structure, which means that the tidal barrages are used to generate electricity, and also to reduce flooding in low-lying areas of land.

Water level is controlled (the barrage can hold water back, or can release it if needed to produce electricity).

Tidal barrages also have some drawbacks because they require high initial costs, and they can also affect marine life by altering the quality of the seawater in estuaries.

2. Tidal Fences

Tidal fences use vertical or horizontal underwater turbines and they represent a much cheaper technology compared to tidal barrages because they don’t require the construction of a large reservoir.

They actually work like underwater windmills that use the movement of the tides (instead of wind) to spin the turbines and generate energy.

3. Tidal Turbines

Tidal turbines look pretty similar to wind turbines, but they are way more robust because the density of the water is much higher (832 times higher) compared to the density of the air, so they can withstand very strong underwater tidal currents.

Electricity is generated when the kinetic energy of the tidal currents is turned into mechanical energy (the spinning turbines) and then into electrical energy by the generators.

Compared to a wind turbine, a tidal turbine can generate much more energy due to the fact that the kinetic energy of the tidal currents is much higher than the kinetic energy of the wind.

Benefits of Tidal Power Plants

1. Is a predictable energy source

Because the tidal patterns in our oceans are well known today, tidal energy is a very predictable energy source, and represents the ideal source of power for the grid because is both clean and reliable.

Tides a renewable resource

Tides are considered a renewable resource for mankind,

2. Is a renewable source of power

Being produced by the rotational forces of the planet combined with the gravitational forces of the Moon and the Sun, tides represent a renewable energy source because they rely on an endless resource of power.

3. Is a reliable source of electricity for the grid

Other renewable energy sources such as solar and wind are way more unpredictable, and this is the reason why the energy produced by solar or wind power plants needs to be paired with other sources of power (usually fossil) to meet the grid’s demand for energy.

However, the energy produced by a tidal power plant is more like the energy produced by a hydroelectric power plant that doesn’t need to be paired with other energy sources.

Drawbacks of Tidal Power Plants

It seems that any source of energy (including the tidal power), has its disadvantages despite being a renewable energy source.

1. Tidal power plants affect marine life

All tidal power plants can affect marine life because migratory fishes can be killed when marine currents reach the spinning underwater turbines.

Building a dam on a river estuary raises environmental concerns because it will seriously affect the biodiversity in the region.

2. Requires certain conditions that limit their spread on a large scale

Tidal power plants require specific geographical requirements (the difference between the high and the low tide must be at least 16.4 feet or 5 meters), which limits the number of coastline areas suited for tidal power generation.

3. Very high initial investments

The initial investment in a tidal power plant is very high, and because the coastal areas that are ideal for tidal energy production are usually located in remote areas, this will increase the investment even more.

Global Tidal Energy Potential

Sadly, the current technology used to generate tidal power requires certain conditions to be accomplished, to make a coastal area ideal for tidal energy production.

A difference in height between the low and the high tide of over 16 feet (5 meters) is not that easy to find, and this is the reason why tidal power occupies today only a fraction in the global energy mix.

The current potential to generate electricity using all the tides available on the planet is around 3,000 GW (gigawatts), which equals 3 TW (terawatts).

However, if we only consider the coastal areas that are ideal for tidal power generation (which are suitable for the construction of tidal barrages, tidal fences and tidal turbines), the potential is reduced to a value of only 120 to 400 GW.

The global energy demand for power exceeding 26,000 TWh (Terawatt hours) in 2020, means that the real potential to produce electricity using the current tidal technology is very limited.

Future Tidal Technology

However, future tidal technology may use underwater turbines installed in different areas of the ocean to use the strong underwater currents and produce energy exactly like wind turbines.

The new tidal technology (using fully built-out tidal power systems) that will no longer use only the ideal coastal areas, will increase the potential for energy generation up to 3,800 TWh, which can cover about 15% of the current global demand for electricity.


Tidal energy is another form of hydropwer, which is showing us that the world ocean is not only a source of life, but also a source of limitless clean electricity.

Tidal energy along with the other renewables can help us reduce the use of fossil fuels, which can make the air, the soil and the water on the planet clean again (like they were before the industrial revolution).

Article written by:

I am a writer and reporter for the clean energy sector, I cover climate change issues, new clean technologies, sustainability and green cars. Danny Ovy

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