Description

Tidal Energy

Description: "Explore the potential and challenges of tidal energy, a renewable power source driven by the gravitational pull of the sun and moon, with a focus on India's prospects."

What are tides?

•  Tides are generated through a combination of forces exerted by the gravitational pull of the sun and the moon and the rotation of the earth. 

•  The relative motion of the three bodies produces different tidal cycles which affect the range of the tides. In addition, the tidal range is increased substantially by local effects such as shelving, funneling, reflection and resonance. 

Principle of Tidal Energy

•  Energy can be extracted from tides by creating a reservoir or basin behind a barrage and then passing tidal waters through turbines in the barrage to generate electricity.

•  One way tidal energy is captured is with the use of tidal turbines. They utilize turbines with short but strong blades that spin as the tides move and then transmit their energy to an electricity generator.

•  Another way tidal energy is captured is with the use of tidal barrages. Tidal barrages are special dams that take advantage of the difference in height between low and high tides. Tidal barrages are built across an estuary or bay. When the tide comes in and the sea level rises, water passes through the dam and becomes trapped in a basin. When the tide goes out, gates within the dam release the water, allowing it to flow through turbines that spin and transfer energy to electric generators.

Favourable conditions 

•  Tidal energy is extremely site specific requires mean tidal differences greater than 4 meters and also favorable topographical conditions, such as estuaries or certain types of bays in order to bring down costs of dams etc. 

Advantages

•  This source of energy doesn't generate waste or harmful emissions.

•  It is an inexpensive source of power.

•  As tides are predictable, the power generated from them is more reliable than sources like wind energy.

•  The structure built to tap tidal energy can also act as a protective barrier for the coastline during a storm..

•  Utilization of tidal power will lessen the use of nuclear power, which is costly and involves a lot of risk.

Problems Faced in Exploiting Tidal Energy

•  Intermittent supply - Cost and environmental problems, particularly barrage systems are less attractive than some other forms of renewable energy. Global estimates put the price of generation at 13-15 cents/kWh (no Indian estimates available) 

•  Cost - The disadvantages of using tidal and wave energy must be considered before jumping to conclusion that this renewable, clean resource is the answer to all our problems. The main detriment is the cost of those plants.

•  The altering of the ecosystem at the bay - Damages like reduced flushing, winter icing and erosion can change the vegetation of the area and disrupt the balance. Similar to other ocean energies, tidal energy has several prerequisites that make it only available in a small number of regions. For a tidal power plant to produce electricity effectively (about 85% efficiency), it requires a basin or a gulf that has a mean tidal amplitude (the differences between spring and neap tide) of 7 meters or above. It is also desirable to have semi-diurnal tides where there are two high and low tides everyday. A barrage across an estuary is very expensive to build, and affects a very wide area - the environment is changed for many miles upstream and downstream. Many birds rely on the tide uncovering the mud flats so that they can feed. There are few suitable sites for tidal barrages.

•  Only provides power for around 10 hours each day, when the tide is actually moving in or out.

•  Present designs do not produce a lot of electricity, and barrages across river estuaries can change the flow of water and, consequently, the habitat for birds and other wildlife.

•  Expensive to construct.

•  Power is often generated when there is little demand for electricity.

•  Limited construction locations.

•  Barrages may block outlets to open water. Although locks can be installed, this is often a slow and expensive process.

•  Barrages affect fish migration and other wildlife- many fish like salmon swim up to the barrages and are killed by the spinning turbines.

•  Fish ladders may be used to allow passage for the fish, but these are never 100% effective.

•  Barrages may also destroy the habitat of the wildlife living near it.

•  Barrages may affect the tidal level - the change in tidal level may affect navigation, recreation, cause flooding of the shoreline and affect local marine life.

•  Tidal plants are expensive to build.

•  They can only be built on ocean coastlines, which mean that for communities which are far away from the sea, it's useless.

Tidal energy potential in India 

•  India is estimated to have a potential of around 54 gigawatts (GW) of ocean energy – tidal power (12.45 GW) and wave power (41.3 GW) – but it is yet to be of practical use as the Indian government’s Ministry of New and Renewable Energy (MNRE) says the estimated potential of tidal and wave power is “purely theoretical and does not necessarily constitute a practically exploitable potential”.

•  According to the study, while the Gulf of Kambhat and Gulf of Kutch near Gujarat have an estimated potential of 7000 MW and 1200 MW, respectively, even the Gangetic delta in Sunderbans in West Bengal has a potential of 100 MW.

•  India commissioned its first ocean energy system (150-kW) at Thiruvananthapuram (Kerala) in 1983. 

•  In 2010 Kalpasar Tidal Power Project at The Gulf of Khambhat was identified as a promising site for tidal power generation by UNDP Expert.

•  In Jan 2011, the state of Gujarat announced plans to install Asia’s first commercial-scale tidal current power plant; the state government approved the construction of a 50 MW project in the Gulf of Kutch

•  India's maiden Ocean Thermal Energy Conversion (OTEC) project will be commissioned in early 2019 in Kavaratti, capital of the Lakshadweep. It is expected to generate around 200 kW.