Tidal Energy

Tidal energy is a form of renewable energy which is created by converting energy from tides into electricity using various methods. Tides are more predictable than the wind and therefore the sun. Although tidal energy is renewable energy, it has traditionally suffered from relatively high cost and limited availability of web sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and enhancements, both in design and turbine technology indicate that the entire availability of tidal power could also be much above previously assumed which economic and environmental costs could also be brought down to competitive levels.

The Rance Tidal power plant in France is the world’s first large-scale tidal energy station. It became operational in 1966. It was the most important tidal power plant in terms of output until Sihwa Lake Tidal power plant opened in South Korea in August 2011.

The Principle behind Tidal Energy

Tidal energy is generated from the Earth’s oceanic tides. These tidal waves are the forces which form due to gravitational attraction exerted by celestial bodies. These forces create corresponding motions or currents within the world’s oceans.

Due to the strong attraction to the oceans, a bulge within the water level is made, causing a short-lived increase in water level. Now due to Earth’s rotation, this huge volume of ocean water meets the shallow water adjacent to the shoreline and creates a tide. This natural phenomenon is repetitive and takes place in an unfailing manner, due to the consistent rotation of the moon’s orbit around the earth.

A tidal generator is required to convert the energy of tidal flows into electricity. The potential of a site for tidal electricity generation is directly proportional to greater tidal variation and better tidal flow velocities. These together can dramatically increase the tidal energy generation. As we know that Earth’s tides take place due to the gravitational force of Earth with the Moon and Sun, so the tidal energy is practically inexhaustible and classified as a renewable energy resource. Movement of tides causes a loss of energy within the Earth-Moon system.

Methods of Generation of Tidal Energy

Tidal energy formation is often classified into four generating methods:

A) Tidal Stream Generator

Tidal stream generators make use of the kinetic energy of moving water to power turbines, in a similar way to wind turbines that use the wind to power turbines. Sometimes existing bridges are used to built tidal generators or some are entirely submersed, thus avoiding concerns over the impact on the natural landscape.

B) Dynamic Tidal Power

Dynamic tidal power (or DTP) may be a theoretical technology that might exploit an interaction between potential and kinetic energies in tidal flows. It proposes that very long dams (for example, 30–50 km length) be built from coasts straight out into the ocean or ocean, without enclosing a neighbourhood.

C) Tidal Barrage

Tidal barrages make use of the potential energy in the difference in height (or hydraulic head) between high and low tides. When the ocean level rises and therefore the tide begins to return in, the temporary increase in tidal power is channelled into an outsized basin behind the dam, holding a large amount of potential energy. With the receding tide, this energy is then converted into energy.

D) Tidal Lagoon

A new tidal energy design option is to construct circular retaining walls embedded with turbines that can capture the potential energy of tides. The created reservoirs are almost like those of tidal barrages, except that the situation is artificial and doesn’t contain a pre-existing ecosystem.

Rance Tidal Power Plant in France

In 1966, Électricité de France opened the Rance Tidal power plant, located on the estuary of the Rance River in Brittany. It was the world’s first tidal power station. For the long 45 years in history, this plant remained the most important tidal power plant within the world by installed capacity. It has 24 turbines with a reach peak output of 240 megawatts (MW) and average 57 MW, a capacity factor of approximately 24%.

Tidal Power Development in the UK

The world’s first marine energy test facility was established in 2003 to start out the event of the wave and tidal energy industry within the UK. The ECU Marine Energy Centre (EMEC) located in Orkney, Scotland, has supported the deployment of more wave and tidal energy devices than at the other single site within the world. EMEC provides a spread of test sites in real sea conditions.

Tidal Energy Project in India

India has reportedly decided to not proceed with the proposed tidal power station developments in states of Gujarat and West Bengal. The reason behind it was financial challenges in the implementation of those projects. Based on the studies, there’s an estimated potential of about 8000 MW of tidal energy, with 7,000 MW within the Gulf of Khambhat, 1,200 MW within the Gulf of Kutch in Gujarat, and about 100 MW within the Gangetic delta in Sunderbans in West Bengal.

Prominent Tidal Energy Power Stations of the world

The first tidal power plant of the planet became operational in 1966, La Rance in France. It has an installed capacity of 240 MW and is additionally the second largest tidal plant within the world. Sihwa Lake tidal power plant in South Korea is that the world largest tidal power plant with an installed capacity of 254 MW, came up in 2011. Annapolis Royal generating station, Nova Scotia, is the first tidal power site in North America. It opened in 1984 on an inlet of the Bay of Fundy. It has 20 MW installed capacity.

Issues and Challenges

A) Environmental Challenges

Tidal energy has some adverse effects on marine life. The rotating blades of the turbine are very dangerous. It can accidentally kill swimming sea life, although projects like the one in Strangford feature a security mechanism that turns off the turbine when marine animals approach. However, this feature causes a serious loss in energy due to the quantity of marine life that passes through the turbines. This environmental factor is divided into 3 parts.

1) Tidal Turbines

In tidal turbines, the primary concern regarding tidal energy harness is the blade strike and entanglement of marine organisms. As high-speed water increases the risk of marine lives being pushed near or through these devices.

2) Tidal Barrage

Making of a barrage may change the shoreline within the bay or estuary, affecting a large ecosystem that depends on tidal flats. Inhibiting the flow of water in and out of the bay may cause additional turbidity and less saltwater. It can end in the death of fish that act as a vital food source to birds and mammals.

3) Tidal Lagoon

Usually the risk associated with tidal lagoon is blade strike on fish attempting to enter the lagoon, the acoustic output from turbines, and changes in sedimentation processes.

B) Corrosion

Saltwater causes corrosion in metal parts. It is often difficult to take care of tidal river generators thanks to their size and depth within the water. Corrosion may cause mechanical fluids, such as lubricants leak out, which may be harmful to the marine life nearby.

C) Cost

Tidal Energy requires an expensive initial setup. Its high cost is one of the reasons that tidal energy is not a popular source of renewable energy.

FAQs about Tidal energy

Q.1. Which type of turbine is commonly in use in tidal energy?

Answer – The Kaplan turbine is a propeller-type reaction turbine. It is usually immersed completely in the fluid it derives energy from.

Q.2. Is tidal energy expensive?

Answer – Any subsea equipment needed to harness tidal energy is going to be expensive. Also, it tends to drive building costs to be anywhere between 3 to 15 million dollars and sometimes more.

Q.3. How efficient is tidal energy?

Answer – Tidal energy is 80% efficient when it comes to converting water energy into electricity.