Tidal Power

So, What is Tidal Power?

Now we've recapped tides; we can begin to explore tidal power.

Tidal Power Generation

Energy cannot be created or destroyed – the amount of energy in the universe will always remain constant. However, energy can be transferred from one form or object to another.

Tidal energy is a form of kinetic energy – i.e., the energy of movement. Tidal power is generated by the force of the moving tides pushing against a turbine.

The rotor shaft of a turbine is attached to a generator, which converts the kinetic energy of the rotor into electrical energy. And thus, tidal power!

Tidal Power Turbines

Tidal turbines are installed on the sea floor. Water is approximately 800 times more dense than air, so tidal turbines need to be as sturdy as possible. The extra weight makes tidal turbines expensive to build compared to other forms of renewable energy generation.

However, the extra building costs soon pay for themselves. Tidal turbines can capture more energy using the same size blades as a wind turbine.

Tidal Power Plants

There are three types of power plant used to generate electricity from the tides:

• Barrages
• Lagoon construction
• In-stream turbines.

Tidal Barrages

A tidal barrage is a large dam-like structure, constructed across tidal rivers, bays, and estuaries. Turbines are attached to the underside of the dam.

The barrage gates are opened as the tides begin to rise, then closed once high tide has been reached, creating a pool. The trapped water is gradually released, spinning the turbines as it travels back out to sea. Engineers control the release to ensure a steady rate of energy generation.

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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