Harnessing Tidal Waves for Electricity Generation

The world’s oceans and seas are excellent sources of renewable energy owing to the power contained in the wave and tidal movements. Harnessing the kinetic energy from wave motion and tidal flows and using it for electricity generation will help augment the supply of fossil fuels and other renewables.   

However, the construction of infrastructure associated with tidal energy isn’t moving as fast as those connected with other renewable sources like wind farms and hydroelectric plants. One of the reasons for the delayed adoption of technology is the cost involved in capturing tidal power.   

Subsea equipment and building expenses for a tidal project require substantial capital, making the technology a costly proposition. Still, the investment will surely pay off in the long run, especially since the world needs as many alternative power sources as possible.   

What is Tidal Energy?

Tidal energy is created by the movement of ocean tides and currents. The rise and fall of the water also called tidal flow, is a form of kinetic energy that can be used to generate electricity. But first, that energy must be captured. While wind turbines harness wind power and solar panels absorb the sun’s energy, tidal turbines are instrumental in harvesting the energy contained in the tides and currents. 

How Do You Obtain Tidal Energy

Harnessing the power of the tides involves several methods.

Tidal turbines

Tidal turbines operate like wind turbines, except they work under the water’s surface while their wind counterparts work above it. The moving air spins wind turbines while ocean currents turn the blades of tidal turbines. Fixed to the sea bed, the turbines take advantage of the strong tidal flow in the area.   

The force of the current pushes the turbine’s blades, which then spin a rotor connected to a tidal generator. The power coming from the tidal generators is then used for electricity generation.   

Because water is 800 times denser than air, tidal turbine rotors are smaller than those for wind turbines. As such, they can be positioned much closer together, which means they occupy less space.   

Tidal barrages

A tidal barrage is a structure that’s similar to a dam. It’s typically installed at tidal inlets or lagoons that experience a tidal range of over 5 meters. It usually consists of sluice gates, turbines, dams, and ship locks.   

Sluice gates in a tidal barrage control water level and rate flow. They allow the water to come in during high tides and flow out during low tides through tidal turbines positioned at the bottom of the structure.   

A tidal power system using barrages generates electricity using the same principles employed in hydroelectric plants, except that the tidal currents flow in both directions instead of moving from an area of high elevation.   

Tidal fences

A tidal fence combines the features of a tidal barrage and a tidal turbine. While tidal turbines are installed individually on the sea bed, tidal fences are a string of linked vertical axis turbines set up on the ocean floor.   

Because of the moon’s gravitational pull, the tides ebb and flow, and the movement of the water produces a significant amount of energy. Tidal fences capture this energy. Like with tidal barrages, the force of the tidal currents moving through the turbine blades generates electricity. But unlike a tidal barrage that blocks the flow of water, tidal fences let the water through.   

Tidal Energy Cost

Several factors determine the construction and maintenance costs of any project, especially those involving extensive infrastructure. For tidal power, the condition and location of the tidal power plant or tidal power station will affect the upfront costs of building the facilities that will harness tidal energy. 

In general, tidal turbines are more capital-intensive than those used for offshore wind projects, and a tidal power plant is one of the most expensive renewable facilities. The high capital outlay primarily comes from the intricate and extensive engineering work needed to construct, install and connect the power plant to the electric grid. 

Being a relatively new technology, there are limited data from which to draw definite figures regarding costs. Examining several existing tidal energy projects helped provide financial guidance regarding tidal power’s upfront and maintenance costs. 

To generate sufficient power to make the investment worthwhile, tidal energy in areas like Canada costs approximately $0.66 Canadian per kWh to install. In contrast, it takes around $0.2-0.3 per kWh to build turbines for offshore wind projects. 

In general, generating electricity for tidal energy typically costs two to nine times higher than the peak average price for wind energy. 

Tidal Power Plants in the World

To better understand if tidal energy is worth the investment, let’s take a look at some of the largest tidal power plants in the world. 

Sihwa tidal power station (South Korea)

This tidal power station is the most extensive and expensive tidal energy installation globally, with an installed capacity of 254MW. Built-in 2011, it required a capital amounting to $298 million.   

Comprised of 10 generators, it turns tidal power into electricity amounting to over 550 GW a year using submerged bulb turbines.    

Analysis of the construction costs and its generated capacity shows that the Sihwa tidal power plant costs $117 per kWh to install. Meanwhile, consumers pay $0.02 per kWh for the electricity it produces.   

La Rance tidal energy station (France)

This tidal power plant, which is located at the mouth of the Rance River in Brittany, France, began operation in 1966, making it the world’s oldest tidal energy station in the world. It is also the second-largest tidal project in the world.  

At the time of construction, the power facility required a capital outlay of $115 million. Adjusting the said amount for inflation, the cost of tidal power from this power plant in recent times is $382 per kWh, and the electricity it generates ranges between $0.04 to $0.12 per kWh.   

Annapolis Royal Generating Station (Canada)

Located in the Bay of Fundy in Nova Scotia, Canada, this tidal energy station is the third-largest in the world. Construction commenced in 1980, and the power station began producing energy in 1984.  

During the plant’s operation, its peak capacity was 50 gigawatt-hours a year. That’s enough electricity for 4,500 homes.  

The plant was decommissioned in 2019 due to equipment failure.  

Jiangxia Tidal Power Station (China)

This is the largest tidal power station in China and the first one constructed in Asia. The project began in 1974, and the first turbine went into service in 1980, with a peak capacity of 500 W.  

The addition of more turbines over the years added to the tidal power station’s capacity, which now stands at 6.5 GWh a year.  

Kislaya Guba Tidal Power (Russia)

Constructed in 1968, the Kislaya Giba Tidal Power station had an initial capacity of only around 0.4MW. It was closed down for a decade, and upon reopening in 2004, new equipment and technological advances led to an increase in power production. Its capacity now stands at 1.7 MW.  

Is Tidal Energy Worth it?

Although tidal power tends to be more predictable than either solar or wind power, the tidal range usually varies between sites. Globally, the variation ranges between near zero to over 16 meters (52 feet). Moreover, tides ebb and flow depending on the gravitational pull exerted by the heavenly bodies. This means that not all areas are ideal sites for harnessing the power of the tides.   

On average, compared to other more popular renewables like solar, wind, geothermal, and hydropower, tidal energy displays a lower load factor, usually ranging between 20%-35%. That’s because a tidal energy plant operating during low tide generates power only half the time. For economical operation, the tidal range must be at least 7 meters.   

Tidal power generation is also limited to the period when the tides change because the kinetic energy comes from the water movement during those times. Thus, maximum electricity generation from tidal energy plants occurs only around every 12 hours, as the tides ebb or flow. In the 6 hours between the changing of the tides, no electricity generation occur.   

When it comes to cost, using tidal power for electricity generation is less competitive than utilizing other renewable energy providers. The lower load factor and limited generation peak times are the reasons behind this price disadvantage.   

For example, although tidal energy is more reliable than wind power, electricity from tidal power is two to nine times more expensive than the average price of that coming from wind energy.  

Benefits of Tidal Energy

• Environmentally friendly: Tidal energy is a green energy source because a tidal power plant produces electricity without emitting greenhouse gases. Due to the threat of global warming, zero-emissions energy sources play a major role in the fight against climate change.   
• Predictability: The tides ebb and flow due to the gravitational force exerted by celestial bodies that cause the tides to change every day. This predictability makes building facilities and creating systems that work efficiently with tidal power easier.  
• High power output: Because of the water’s density (around 800 times denser than air), tidal turbines generate higher amounts of energy than their wind counterparts of the same size.   
• Efficiency: Due to the density of water, it’s easy to produce electricity using tidal power. Even water speeds as low as 1 meter per second (2.2 miles per hour) can generate power, while wind turbines usually require a rate of 3-4 miles per second (7-9 miles per hour) to begin generating energy. Thus, tidal turbines get the job done even when water conditions are far from ideal.   
• Renewability: The tides always flow, and they do so in numerous locations across the globe. Moreover, harnessing the power created by tidal flows doesn’t diminish the energy they can generate in the future and doesn’t deplete the source. That makes tidal energy genuinely renewable.   

Drawbacks of Tidal Energy

• Cost: The technology behind tidal energy entails high costs. Tidal power plants are typically situated at sea. Thus, they need to be sturdy, which causes the construction expenses to exponentially increase. The components and equipment should also be made from more expensive corrosion-resistant materials.  
• Impact on marine life: Fish and other sea creatures can get stuck in the turbines, and the barrages can disrupt the water’s natural flow. 
• Location limits: Tidal power stations need to be constructed near coastlines where the currents are most robust, thus limiting the sites to coastal states. In some instances, the stations are far from the grid, making it more costly to transport the electricity they generate.  
• Maintenance: Because of their proximity to the sea, corrosion can wreak havoc on the machinery, so regular and more intensive maintenance is necessary.  

FAQs

Final Thoughts

Harnessing the force generated by the tides will boost the energy reserves coming from clean and green sources. This is a welcome scenario as the frequency and impacts of climate change are escalating.   

However, because tidal energy is a relatively new technology, many challenges for its adoption exist. Economically, tidal power looks uncompetitive due to the enormous capital outlay required for the infrastructure. Electricity rates from tidal power plants are significantly more expensive, deterring utilities from adding tidal energy into their power mix.   

Still, the future doesn’t look bleak for this renewable technology. As the US recognizes the need for more clean energy sources, funding for tidal energy will likely increase. This is a welcome development and is what this renewable source needs to gain traction and become one of the go-to green energy providers.   

Updated on 12-06-21