Wind, solar, hydropower, and other types of renewable energy are becoming a major part of the green energy transition around the world. The Texas power grid alone gets up to 38% of its electricity from zero-carbon energy sources. But there’s one type of energy you don’t hear about a lot: tidal energy.
Tidal energy is derived from the rise and fall of ocean waters, so it’s more predictable than other types of renewable energy and less harmful to the environment than fossil fuels like crude oil, coal, and natural gas. So why isn’t it being used more widely for power generation?
Let’s take a look at the ins and outs of tidal energy and why there are obstacles to rolling out tidal energy generation in many parts of the world.
What Is Tidal Energy?
Tidal energy refers to energy produced by the natural movement of the ocean, usually via the installation of tidal turbines. These turbines generate electricity as the current alternates between high tide and low tide.
Tidal energy can take the form of kinetic energy or potential energy. The difference in the water level is considered potential, or stored energy, while the movement of the current is considered kinetic energy.
Since tides are caused by the gravitational pull of the moon, they aren’t dependent on the Earth’s weather systems the way that solar power and wind energy are. High and low tides occur naturally at predictable times of the day, making tidal power a good candidate for electricity generation in areas with sufficient tidal range.
How Is Tidal Energy Generated?
Tidal energy is produced using tidal turbines, which are very similar in design to wind turbines except that they are moved by tidal currents. Water is a more powerful source of energy than wind energy because it’s denser and can produce more force. There are three different kinds of tidal energy systems used around the world. Let’s take a closer look at each one.
Tidal Barrage
A tidal barrage looks a lot like a hydropower dam, except it’s designed to open and close depending on the flow of the tides.
As the tide flows in, the gates are left open to allow the ocean current to fill the area behind the dam. Then the gates are closed, trapping the water in the lagoon.
The water is allowed to flow back into the ocean at a controlled rate, passing through turbines on the way – just like with a hydroelectric dam on a river.
Tidal Stream
Tidal streams are areas in which the tides naturally produce a strong ocean current. By installing tidal turbines at strategic locations in the stream, they can be used to generate electricity without the need for large-scale infrastructure.
Tidal turbines can be placed on the seafloor but need to be positioned in such a way as to avoid obstructing shipping lanes or the natural flow of sediment to the seabed.
Tidal Lagoon
The third tidal energy technology is a tidal lagoon. In this case, tidal turbines are placed in a natural lagoon rather than creating one with a man-made barrage.
This approach is less destructive than building a barrage but doesn’t generate as much power, so there aren’t any tidal lagoon power systems currently in operation.
Why Isn’t Tidal Power Used More Often?
If tidal energy is such a reliable way to produce electric power, why isn’t it more popular as a renewable energy source? Although there are a handful of tidal energy projects on the horizon, so far, tidal power plants are few and far between.
Here are three reasons why tidal energy production is still in its infancy.
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Insufficient Locations
Tidal power plants can’t be built just anywhere on the coastline. According to the U.S. Department of Energy, suitable locations need to have at least 10 feet of tidal range between high and low tide.
Even in countries with access to the ocean, there simply aren’t enough places where tidal energy can be installed to make them a viable option.
When a suitable location is found,tidal energy projects may still face legal challenges and regulatory hurdles before they can begin development.
Environmental Impact
Tidal energy projects can also have a negative impact on the environment if steps aren’t taken to protect marine life and fragile ecosystems.
Although tidal power plants don’t have any greenhouse gas emissions, there may be other environmental effects, such as changes to the sea level or water quality.
Large-scale barrage projects can be especially disruptive to the ecosystem since they may alter the salinity of the lagoon or interfere with the movement of marine life.
Cost of Development
Finally, tidal power projects are simply more expensive than other clean energy sources relative to the amount of power they generate.
Tidal turbines must be more durable than wind turbines in order to withstand ocean currents, while tidal barrage projects can cost millions to construct.
According to an estimate by the Department of Energy, tidal energy costs $130‒280 per megawatt-hour (MWh), while wind energy can cost as little as $20 per MWh.
Currently, there are no marine renewable energy projects in operation in the U.S., but that could change if the technology becomes more cost-effective.
What Is Wave Energy?
Tidal energy isn’t the only type of energy that humans can harvest from the sea. Wave energy can also be used to generate electric power. Whereas tidal energy is caused by gravity, wave energy is produced by the impact of wind on the ocean surface.
Wave energy can be collected using one of several methods:
- An oscillating water column (OWC) that uses compressed air to drive a turbine
- A pivoting flap device in which the wave flows in and out of a chamber
- Tapered channel devices, in which wave energy drives seawater into a reservoir
- A buoyant moored device that rotates on the surface of the water
Although the U.S. doesn’t have any tidal power plants, it has tested out wave energy devices in Hawaii and Oregon. These devices are more mobile than turbines and can be deployed further offshore. Since they can float and rotate, they can harness wave energy in both horizontal and vertical directions. If testing is successful, they can be connected to the power grid using undersea cables.
How Many Tidal Power Plants Are There In the World?
Despite their limitations, there are at least eight tidal power stations currently in operation, with more projects on the way in Canada and the United Kingdom. Let’s take a tour of the world’s biggest tidal energy stations to see what they look like in action.
Sihwa Lake Tidal Power Station (South Korea)
The Sihwa Lake Tidal Power Station in South Korea is the largest tidal energy project currently in operation, with a generating capacity of 254 MW.
To put that number into perspective, the Bluemull Sound tidal stream array in Scotland only produces 0.4 MW and is a more typical example of tidal power.
The Sihwa Lake generator was opened in 2012 at a cost of $560 million U.S. dollars. The South Korean government chose this location for the project because the water quality had already declined after a seawall was built in 1994.
The operation of the power plant has improved the water quality due to increased circulation, making this a successful example of tidal power in action.
La Rance Tidal Power Station (France)
The oldest tidal power station currently in use is the La Rance Tidal Barrage in Brittany, France, which has been active since 1966. It’s just a few megawatts shy of the Sihwa Lake power station, with a generating capacity of up to 240 MW.
It’s situated at the mouth of the Rance River, which has an average tidal range of 26.2 feet and a maximum range of 44.3 feet – perfect for power generation. Despite that, it still only generates 0.012% of the country’s power.
Unlike the Sihwa Lake power station, the La Rance station has had detrimental effects on the ecosystem, primarily through silting and changes in salinity.
MyGen Tidal Power Plant (Scotland)
Although nowhere near the size of the previous two tidal power plants, the MyGen Tidal Power Plant in Scotland is home to the world’s largest tidal turbine.
At 680 metric tons and over 240 feet long, it can generate two megawatts of power, which is enough to power 2,000 homes for a year.
This turbine is just one of a growing number of turbines that will be added to the array, making it the largest project of its kind in the United Kingdom.
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Pempa’q In-stream Tidal Energy Project (Canada)
Nova Scotia’s Bay of Fundy coast has been home to several tidal energy projects, including the Annapolis Royal Generating Station, which closed in 2019. At its peak, the station generated 200 MW but had significant impacts on marine life.
The upcoming Pempa’q In-stream Tidal Energy Project is expected to produce nine megawatts of power in all, using new technology, which offers a more mobile and adaptable solution for capturing ocean energy.
Meanwhile, the Fundy Ocean Research Centre for Energy (FORCE) in Nova Scotia is performing environmental research and monitoring to ensure that this and future tidal energy projects minimize their impact on the environment.
Power Your Home With Renewable Energy
Tidal energy is one of the most powerful and reliable sources of energy on the planet. But high upfront costs and potential environmental impacts mean that it isn’t likely to make up a large part of our energy supply any time soon. Other renewable energy resources, like wind and solar, are more cost-effective per megawatt-hour.
If you’re looking to power your home with renewable power, sign up for an electricity plan with Just Energy. Our green energy plans use Renewable Energy Credits to ensure that 100% of your energy usage is offset by renewable power. Simply enter your ZIP code to compare your options.
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