Tidal Power

Fig. 1 - Tide diagram

Lagoon Construction

Tidal lagoons are bodies of water partly enclosed by a natural or man-made barrier. Natural tidal lagoons are often found at estuaries, where they receive a constant supply of freshwater.

A lagoon power plant would function much like a tidal barrage; trapping water and controlling its release through turbines.

In-stream Turbines

Tidal turbines are placed directly into a tidal stream.

In-stream tidal turbines are most effective when placed in a shallow tidal stream. This maximises energy production, and causes minimal disturbance to ships and marine life.

Advantages of Tidal Power Services

Like many other forms of renewable energy, tidal power is carbon-free, producing no greenhouse gases or other pollutants. But tidal power services have a few other traits that make them stand out from the crowd.

Reliability

Tides go in and out like clockwork every day, regardless of the season or weather. This makes tidal power a predictable and reliable source of renewable energy.

Energy Efficient

Tidal power has a higher energy density than most other forms of renewable energy.

Furthermore, tidal turbines operate at 80% efficiency – higher than solar panels or wind turbines.

Longevity

Tidal power plants can last a long time. The average lifespan of a tidal barrage is 100 years – four times longer than a wind or solar farm!

Limitations of Tidal Power Services

Producing renewable energy using the power of the tides is a newly emerging field, but one with great potential.

However, there are very few commercial-sized tidal power plants worldwide. Why is this?

Tidal Ranges

Not all coastlines are suitable locations for tidal power plants. This is because the tidal range varies around the world.

Using tidal power as a form of renewable energy is most suitable in an area with large tidal ranges. These areas are typically coastal locations. Land formations and topology can also affect tidal range – land masses that funnel water, restricting its ability to dissipate, typically produce large tidal ranges.

For a tidal power plant to be economically viable, the coastline requires a tidal range of at least ten feet. Some parts of the world experience small tidal ranges of only three feet, such as the Gulf of Mexico, the Caribbean, and the Mediterranean. In these places, the construction of tidal power plants would not be worthwhile.

Impacts on the Environment

Tidal power projects also raise ecological concerns, which vary depending on the type of power plant.

Tidal Barrages

Tidal barrages significantly affect the land in the tidal range. The mean sea level within the barrage increases, whilst salinity inside the lagoon decreases. These changing conditions affect the plants and animals that can inhabit the area. Fish are other marine animals are often blocked in the lagoon, getting caught in the blades. The feeding grounds of birds are often flooded, so they migrate elsewhere.

Lagoon Construction

This type of power plant has minimal environmental impact. Typically constructed with natural materials, these power plants are submerged at high tides. This allows fish to swim around the structure, but prevents larger animals such as sharks from penetrating the lagoon. A high fish population would support high bird populations.

In-stream Turbines

Installing in-stream turbines can disrupt the tide. The environmental impact depends on the size of both and turbine and the tidal stream. The blades of these turbines turn slowly, to minimise marine life getting caught in the system.

Fig. 3 - In stream turbine

Tidal power converts kinetic energy of the tides into electricity using underwater turbines. It's a renewable, predictable and efficient source of energy, but there are few working plants due to tidal range requirements and ecological impacts.

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^{12. U.S. Energy Information Administration, Tidal power, 2021}