What is Tidal Energy and How is Tidal Energy Converted into Electricity?

What is Tidal Energy?

As most economies witness rapid expansion, demand for power is projected to increase significantly. Though most economies have invested in fossil fuels, renewable and sustainable sources present great possibilities for cheap and reliable electricity. One energy resource that ranks among the top renewable and sustainable sources is tidal energy.

Tidal energy or tidal power is a form of renewable energy obtained due to alternating sea levels. The kinetic energy from the natural rise and fall of tides is harnessed and converted into electricity. Tides are caused by the combined gravitational forces of the moon, sun, and earth. However, tides are influenced most by the moon. The moon’s gravitational force is so strong that it tugs the ocean into bulge. The high and low tides create tidal currents, which are essential in generation of this kind of energy mostly prevalent in coastal areas. Tidal energy is considered a renewable energy resource because the oceans and seas will remain until the end of time and tides are highly predictable.

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Tidal energy generation plants are most commonly installed along coastlines although offshore plants are increasingly becoming popular. Coastlines are preferred because they receive 2 high tides and 2 low tides every single day. To generate electricity, the disparity in water levels must be at least 5 meters.

Tidal power has great potential for future as tides can be much more accurately predicted than wind or sun and due to massive size of oceans. Though it available in plenty but harnessing energy from it is not that easy. It suffers from huge investment and limits availability of sites where it can be captured.

How Tidal Energy is Converted into Electricity?

Tidal energy is converted into electricity using three main tidal technologies:

  1. Tidal Turbines

Tidal turbines utilize the same technology to wind turbines. The only difference is that the blades of tidal turbines are way stronger and shorter. So, the best way to compare tidal turbines is underwater windmills. Ideally, the water currents turn the turbine. The turbine is connected to a generator through a shaft. So, when the turbine turns, the shaft also turns. The turning shaft activates a generator, which generates electricity. The initial cost of setting up this tidal stream system is quite on the higher side, not to mention the difficulty in maintenance. However, it remains a cheaper alternative and doesn’t cause environmental degradation compare to other tidal technologies.

  1. Tidal Barrages

Tidal Barrages are the most efficient tidal energy technologies. They resemble dams used in hydropower plants. The difference is they are a lot bigger since they are constructed across a Bay or an Estuary. For the barrage to be able to produce power, the tidal range, which is the difference between low and high tide, has to be more than 5 meters. As the tide enters the system, ocean or sea water flows via the dam into the basin. When the tides subside, the system’s gates close, trapping the water in the estuary or basin. When the tides start to move out, the gates in the dam that consist of turbines, open up, and water begins to flow out hitting the turbines, which eventually turn to produce energy. Construction of tidal barrages involves high upfront capital costs, plus they have devastating effects on the local environment.

  1. Tidal lagoons

This technology has a lot in common with tidal barrages. It’s just that it doesn’t involve a lot of initial capital outlay and it’s friendly to the environment. Tidal lagoon is a power station separated from the rest of the ocean or sea. Its functionality is similar to tidal barrage since when the tide goes up, the lagoon completely fills up. When the tide subsides, the water is allowed to drain out through an opening consisting of turbines. The outward flow of water turns the turbine, which generates energy.

Advantages of Tidal Energy

By taking the time to critically analyze the advantages and disadvantages of tidal energy, you can get a clear picture of whether it’s a sustainable energy resource or not. Below is an outline of the upsides and downsides to tidal energy

  1. It’s environmentally friendly

The fact that tidal energy technologies are installed on the coastlines and offshore makes them good for the environment since land will not be interfered with. Also, tidal energy is a clean source of energy, meaning it doesn’t release any greenhouses gasses to the atmosphere.

  1. It’s renewable energy source

Tides harnessed to produce tidal energy result from the combined gravitational pull of the sun, moon, and earth in conjunction with the rotation of the planet around its axis. This is a natural process that occurs every single day. This means that tides will continue to occur and production of tidal energy will continue until the end of time.

  1. It’s highly predictable

Development of tides is a well-understood cycle. This makes it a lot easier to develop tidal energy systems with the right dimensions. Why?  Because the level of power the system will be exposed to is already determined. Which explains why the capacity of the installed equipment and the entire physical size has completely no energy generation limitations, even though stream generators and tidal turbines used resemble those of wind turbines.

  1. Cost-competitive

Tidal energy technologies once constructed have the potential to generate electricity for many years, which means they are long lasting. Although the upfront costs of setting up a tidal power plant are relatively high, the return on investment will be realized in the long run. A typical example is the La Rance tidal barrage, which is still producing electricity since 1966.

  1. Minimizes over-dependence on fossil fuels

Fossil-based sources of energy such as oil, coal and natural gas emit greenhouse gasses that lead to climate change and global warming. Tidal energy offers a green and renewable alternative to cut back on greenhouse gas emissions.

  1. Offers a sense of protection

Barrages and dams that are utilized to tap tidal energy for the generation of electricity could insulate coastal areas and ship ports from high impact and dangerous tides in the course of bad weather and storms.

  1. It’s quite effective than wind even at low speeds

Oceans currents have the capacity to produce more energy than air currents because ocean water is 832 times denser than air. This means ocean currents applies greater force on the turbines to generate more energy.

Disadvantages of Tidal Energy

  1. High upfront capital costs

Tidal energy technologies are considerably new. Meaning the costs of infrastructure are relatively high at the moment. Experts also project that tidal energy will only start to be commercially beneficial in 2020 with enhancements of innovative technologies.

  1. It’s not completely environmentally friendly

Tidal energy generation systems are thought to harbor some environmental impacts, but they have not been quantified. In addition, these tidal plants produce electricity using tidal barrages that depend on manipulation of sea levels. This means that they have the same environmental impacts as hydroelectric dams.

  1. Problems of efficiency

Generation of tidal electricity wholly depends on tidal surges, which happen twice a day. This means when tides are not happening, there is no production of energy, which is why extra costs must be incurred to set up energy storage systems.

  1. Tidal energy needs Long gestation period

Tidal power plants need a lot of time to be able to produce electricity efficiently. This aspect combined with cost of installation can be unsustainable. A typical example of a tidal power plant that was closed due to time and cost overruns is the UK’s Severn Barrage.

  1. Impact on marine life

The greatest fear among tidal energy systems developers is the impact the plants and turbines will have on the surrounding marine ecosystem. The rotation of turbines and vibrations of the tidal plant could significantly interrupt marine ecosystem and inhibit natural movement of marine life.

Although tidal energy technology is still in its infancy stage, the grave impacts of fossil fuels and the fear of them running out some day means a lot of time and resources will be dedicated towards generation of tidal energy. Even though other renewable and green sources of energy such as sun, wind and geothermal are way ahead, tidal is fast catching up with the pack. Tidal energy is seen as the next big thing once its technology becomes a lot better.

References: Wikipedia , EIA
Image credit: flickr ,

Rinkesh

Rinkesh is passionate about clean and green energy. He is running this site since 2009 and writes on various environmental and renewable energy related topics. He lives a green lifestyle and is often looking for ways to improve the environment around him.