All You Need to Know about Tidal Power
Tidal power, with its innumerable benefits, might just be the sustainable energy form of the future. Let’s see what makes it such a great alternative to fossil fuels.
The world changed forever with the discovery of fossil fuel energy. Ever since the Industrial Revolution of the 18th century, humankind has used fossil fuels do deliver unprecedented affluence to large numbers of people. If back then the biggest challenge was to deliver as much energy as possible to as many people as possible, at present, the greatest challenge is to deliver even more energy without endangering the planet or depleting its natural resources.
Sustainable energy may be an emerging industry, but it is capable of meeting today’s energy demands without putting too much strain on the environment. At present, there are many sources of renewable energy, including solar power, geothermal power, tidal power and wind power that are suitable for both large-scale and small off-grid applications in remote areas.
Many of these sustainable alternatives are still in the infant stages of development, but they show great promise. Tidal power is one such form of renewable energy. Despite the fact that tidal power is not widely used yet, it is more predictable than solar power and wind energy. In the following article we will share the history of tidal power, attempt to eloquently answer frequently asked questions about this form of energy, list its pros and cons, understand how it works and strengthen our newly gained knowledge through the power of example.
TABLE OF CONTENTS:
- Tidal Energy Definition
- Brief History of Tidal Energy
- Frequently Asked Questions about Tidal Energy
- What is Tidal Power?
- How does Tidal Power Work?
- Where is Tidal Power Used?
- How efficient is Tidal Power?
- Where are tidal Power Plants Located?
- Why is Tidal Power Renewable?
- Tidal Power Pros and Cons
- Advantages of Tidal Energy
- Disadvantages of Tidal Energy
- The Environmental Impacts of Tidal Energy
- Interesting Tidal Energy Costs
- The Future of Tidal Energy
Tidal Power Definition
If we are to correctly define tidal power, we must inspect the past. Believe it or not, tidal power has been around for hundreds of years. As a matter of fact, ‘tide mills’ that date back to the Middle Ages can still be found in Europe, demonstrating that this alternative form of energy is quite old. The technology has improved immensely over the year, but it uses the same general concept.
Arguably the clearest and easiest to understand Tidal energy definition was given by Wikipedia:
“Tidal power, also called tidal energy, is a form of hydropower that converts the energy obtained from tides into useful forms of power, mainly electricity.”
Definition of Tidal Power, according to Wikipedia
Brief History of Tidal Power
The general concept of using the waning and waxing of the moon and tides has remained constant throughout the centuries. The history of tidal power stretches well into antiquity: the earliest evidence date back to 900 A.D. Sadly, most of the information from prehistory is shrouded in a veil of anonymity. In ancient times tidal power was harvested by building dams across the opening of a basin. During the rising tide, the basin would fill the dam. The impounded water was channeled through a waterwheel or paddlewheel and used for grinding grain into flour.
In England, tidal power was used to ‘dredge’ shipping channels, as tidally-impounded water would pulse through the channel. As mentioned above, ‘tide mills’ in Europe date back to the Middle Ages. A mill from Suffolk, England, dates back to the 1170, and the oldest tide mill still standing dates today back to 787.
Tide mills were brought to North America with the settlers. Since the eighteenth century, Maine, in particular, benefited from the construction and use of tide mills. Fast-forward to 1921, when a book entitled ‘Tidal Power’ is published by A. M. A. Struben. In this book were outlined several methods of capturing tidal power. One year before this, engineer Dexter Cooper came up with the idea of capturing the power of the tides. Although he found robust funding, the project failed when the stock market crashed in 1929.
Several years later, President Franklin D. Roosevelt, an early supporter of Cooper, tried to implement his concept. However, the projected proved to be too expensive. Despite the fact that it wasn’t implemented, the idea remained in the minds of the people. Several studies followed in Canada and the United States, but France would become the leader in the implementation of tidal energy in the modern era. They were the ones to construct the first tidal power plant in Brittany. The La Rance Tidal power plant has been in continuous operation for over 40 years. It has a capacity of 240 MW, which represents a third of the output of an average coal-fired plant.
Frequently Asked Questions about Tidal Power
Tidal power is one of the most underrated and least known forms of renewable energy. Naturally, people have many questions related to tidal energy: “How does tidal power work?”, “Where is tidal power used?”, “How is tidal power generated?” etc. Let us address several of these questions.
1. What is Tidal Power?
Like geothermal energy, tidal power (or tidal energy), is a predictable form of renewable energy. Tidal power is harnessed by capturing the kinetic energy of the ocean that is released as the Earth orbits the sun. A tide is created when the gravitational effects of the moon and sun on the Earth cause cyclical movements of the seas.
Because humankind has a deep understanding of gravity and the Earth’s movements, tidal power is considered a predictable form of renewable energy. This energy can be harvested in two forms:
- Tidal Streams or adolescent tidal technologies (the flow of water when the tide manifests itself as a tidal current – it ebbs and floods). Energy from tidal streams is extracted with the help of devices that capture the kinetic movement of water (similar to how wind turbines extract power from air currents). As may already know, sea currents are stronger in places where water has to flow through a narrow channel and weaker in protected areas (e.g. gulf, bay, lough, etc.). In theory, capturing sea currents where the tidal stream resource is high will result in higher energy conversion rates.
- Tidal Range or mature tidal technology (the vertical difference between a high tide and its succeeding low time). In order to capture this form of power artificial tidal barrages must be constructed. When the tide floods into the reservoir, the turbines present in the barrage’s barrier will be powered by water and generate electricity. Electricity is produced as the wave retreats beyond the barrier.
2. How does Tidal Power Work?
During a 24 hour cycle, the ocean level will increase until it reaches its highest point twice a day (high tide), and also recede until it reaches its lowest level (low tide), also twice a day. The cycle between high tide and low tide occurs over a period of six hours. There are two reasons why our planet has tides: Earth’s size and the gravitational forces of the Moon and Sun.
The Earth’s Gravitational Forces
For our planet, the most important gravitational forces are the moon (because it’s huge and it’s extremely close to us), and the sun (because it’s terrifyingly huge and far away). Let’s start by considering the moon. Situated at approximately 384,000 km from our planet (measured from the center of the Earth to the center of the moon) is our beloved satellite.
2.1. The Moon’s Gravitational Force
The edge of the Earth that faces the moon is closer than the opposite edge. Doh! But just how closer is it? You know, only 6,370 km (the Earth’s radius). Using some basic math, scientists concluded that the gravitational force of the moon for the edge facing the moon is 3.4% stronger than the gravitational force at the center of the earth.
Furthermore, the force of gravity on the opposing face is 3.2% weaker than the force of gravity at the center of the Earth. The difference in gravitation for the opposing edge, center, and closest edge defines tidal forces.
Under the effect of the moon’s gravitational forces the Earth has a tendency to become flatter at the poles (or wherever moonrise/moonset occurs) and to stretch at the nearest and farthest points (when the Moon is directly overhead). Of course, this force isn’t strong enough to change the shape of Earth’s solid mass (e.g. rocks). But because our planet is covered in 71% water, and water is highly susceptible to the gravitational forces of the moon, it changes shape.
The solid mass on our planet will maintain its spherical form, but the oceans will bulge a few meters around the equator. High tides happen when the Earth passes through the side farthest from the moon and the one closest to the moon. Low tides occur during moonrise and moonset.
2.2 The Sun’s Gravitational Force
The sun also affects also effects tides on Earth. Despite the fact that the tidal forces of the Sun are weaker than those of the moon, they are not to be ignored. During a New Moon or Full Moon, the sun and moon are aligned.
This is the time of the year when oceans have their highest high tides and lowest low tides – spring tides. Alternatively, during the moon’s first and last quarters (when it sits at a right angle with the sun), the ocean has its highest low tides and lowest high tides – neap tides.
It’s extremely important to first understand how tidal power works before you can understand how it is harnessed and transformed into usable energy.
3. How is Tidal Power Generated?
Tidal power is harnessed with the help of various technologies. Although the technology is still at a nascent stage, the potential is enormous.
Scientists say that wave energy resources are abundant between 30 and 60 degrees latitude (in both hemispheres). According to statistics, the coasts of the United States receive around 2,100 terawatt-hours of incident wave power every ear.
At present, there are four types of tidal power generating technologies:
- Tidal barrages (generally situated across the full width of a tidal estuary) leverage the potential energy from the difference in height between high tides and low tides. In order to capture this tidal power, specialized dams are placed strategically. During high tide water that overflows is channeled into a large basin behind the dam. During low tide water recedes and the potential energy captured is converted into mechanical energy (the water is released into large turbines where it generates electricity).
- Tidal lagoons represent a more advanced design option for capturing tidal power. Circular retaining walls embedded with turbines are constructed to capture the potential energy of ocean water. Tidal lagoons are similar to tidal barrages, with one major difference: they are 100% artificial and do not rely on a pre-existing ecosystem. In order to flatten power output, tidal lagoons can have double or triple output. Excess energy is not wasted and can be stored for longer periods of time. (World’s first tidal lagoon: Tidal Lagoon Swansea Bay, Wales, UK).
- Tidal Stream Generators, commonly abbreviated TSGs, fully utilize the kinetic energy of the ever-moving water to power turbines. This type of technology is similar to the technology used to power wind turbines. TSGs represents a convenient solution for capturing tidal power because they can be built into existing structures (like bridges).
- Dynamic Tidal Power (DTP), developed by ARCADIS engineers Rob Steijn and Kees Hulbergen, is an experimental technology that has yet to be put into practice. Nevertheless, it holds great promise for exploiting the interaction between tidal flows and kinetic energies. A DTP proposes long dams (30-50 kilometers) that can be built directly from coasts and into the sea/ocean. In order to capture tidal power, phase differences are introduced across the long dam. This leads to a great water-level differential in shallow coastal seas and the ability to capture oscillating tidal currents like the ones present in China and the United Kingdom. (more information on DTP: Dynamic Tidal Energy Technology Advances)
4. Where are Tidal Power Plants Located?
Tidal Power Plants are generally located in areas that are rich in tidal power. However, because tidal power services are still an immature technology, no clear standard has been set.
At present, sustainable energy pioneers and engineers are experimenting with various locations and designs to find the best solution and encourage full-scale deployment. Here is a list of tidal power plants that are operational or under construction:
Sihwa Lake Tidal Power Station, South Korea (254 MW)
Located less than 4 kilometers from the city of Siheung, on the lake with the same name, sits the world’s largest tidal power plant: the Sihwa Tidal Power Plant.
The facility, which utilizes 12.5km of seawall, began operations in August 2011. Today, its 254MW output capacity is secured by the ten submerged bulb turbines (producing 25.4 MW each) and eight culvert sluice gates.
The Sihwa Lake Tidal Power station was built in seven years (between 2003 and 2010), with an investment of $355.1 million, and has an annual generation capacity of 552.2GWh.
Swansea Bay Tidal Lagoon, UK (240 MW)
This is the world’s largest tidal power project, and upon completion, it will become the third largest tidal power plant in the world. In order to secure an output capacity of 240MW, the Swansea Bay Tidal Lagoon will use a 9.5km-long sea wall/breakwater facility to generate a lagoon cordoning off 11.5 square kilometers of the sea.
Similar to the technology used for the Sihwa Lake Tidal Power Station, Swansea Bay will use reversible bulb turbines to generate tidal power as water passes in and out of the lagoon. With a tidal range of 8.5m and estimated annual power generation capacity of 400GWh, this power plant is expected to power 120.000 homes for the next 120 years. The project is expected to be completed in 2018.
La Rance Tidal Power Plant, France (240 MW)
The tidal power plant with an average tidal range of 8.2m is situated on the estuary of the Rance River, in Brittany, France. This is the world’s oldest (operational since 1966) and second largest tidal power station. The annual generation capacity of the La Rance Tidal Power Plant exceeds 540GWh.
Facility specifications: 145.1 meters long barrage, 163.6 meters-long dye, six fixed wheel gates, 22 square kilometers of facility surface. Energy is produced by the 24 reversible bulb turbines. The La Rance Tidal Power Plant generates enough electricity to serve 130.000 households every year.
Other Tidal Power Plants:
- Annapolis Royal Generating Station, Canada. This tidal power plant, which features sluice gates and blade turbines and has an installed capacity of 20MW, generates 50GWh of electricity every year (powering over 4,000 homes). The facility uses a causeway built in the 1960s that was initially designed to serve as a transportation link.
- MeyGen Tidal Energy Project, Caithness, Scotland. Situated in the Inner Sound of the Pentland Firth is the MeyGen Power Plant. Currently in its first phase of development, the facility has an installed capacity of 86MW, but is expected to reach a capacity of 398MW by 2020.
5. Where is Tidal Power Used?
There are three basic ways of harnessing the power of the ocean. Since ancient times, mankind has used wave energy for transportation. Here are three possibilities in today’s world:
- Tidal Energy. This form of ocean energy occurs when tides come into the shore and are trapped in the reservoirs of dams. For this form of energy to be efficient, there must be a difference between high and low tide of at least 16 feet.
- Wave Energy. The kinetic energy created by the up-and-down movement of ocean waves can be collected and used to power turbines, which in turn create electricity. Most wave-energy systems are very small. We have already discussed wave power in detail in a different article.
- Ocean Thermal Energy. The third utilization of tidal power is ocean thermal energy. This idea uses the temperature differences of the ocean to create energy. A difference in temperature of at least 38 degrees Fahrenheit is necessary between the colder (deeper) and warmer surface of the ocean. Ocean Thermal Energy Conversion (OTEC) is currently used in Hawaii and Japan for demonstration purposes.
6. How Efficient is Tidal Power?
Tidal power is extremely efficient in comparison with other renewable energy sources. Even when it is compared with fossil fuels power plants (efficiency rate of 30%), tidal energy is still more efficient (efficiency rate of 80-85%).
“Tidal energy has an efficiency of 80% in converting the potential energy of the water into electricity.” – Source: NewWorldEncyclopedia
Nevertheless, for this efficiency level to be reached certain conditions must be met: the difference between low and high tide must be at least 7 meters in areas with semidiurnal tides. Even in areas with less-than-perfect conditions, efficiency rate is still extremely high.
7. Why is Tidal Power Renewable?
Tidal energy is considered renewable because it utilizes water and the gravitational energy of the Moon, Sun and Earth. In addition to this, wave power which turns into energy originates in water and wind (which is driven by sunlight).
Now that we have answered these extremely important questions it is time to move to the advantages and disadvantages of tidal power section.
Tidal Power Pros and Cons
Every day, the immeasurable waters of the ocean press and recede along Earth’s coastlines according to the celestial movement of the Sun and Moon. In some areas, like the Bay of Fundy, these tidal movements are particularly pronounced (resulting in spring tides that can reach a height of 15 meters). But there is no perfect energy source and tidal power is no exception. We must, therefore, explore the tidal power advantages and disadvantages in order to fully understand its applications.
Advantages of Tidal Power
Below is a list of tidal power pros:
- Renewable resource (does not require any fuel).
- Operating costs are low. Upfront costs may be high, but operating and labor costs are extremely low, unless something malfunctions.
- Minimal visual impact. Because they are almost completely submerged underwater, tidal energy plants do not damage ‘water views’.
- No greenhouse gas, emissions or ocean pollutants.
- There are currently 20 discovered sites with high tidal energy potential. This doesn’t mean that there aren’t any other decent locations around the world. The Coast of British Columbia alone has 89.
- Extremely efficient. As previously mentioned, tidal power converts around 80 percent of kinetic energy into electricity.
- Environmental impacts are local.
- Predictable energy source. Because tides move constantly throughout the day, tidal plans provide consistent power.
- Can act as a storm surge barrier.
- Reliable solution that can last well over 100 years.
Disadvantages of Tidal Power
Below is a list of tidal power cons:
- Has negative impact on marine mammals, birds and fish migration.
- Crazy expensive to build.
- Like most sustainable energy sources, it is very location specific.
- May restrict access to open water and change tidal level of the surrounding waters.
- Decrease salinity in tidal basins and may disrupt tidal cycles.
- Mud flats, captured dirt, pollution and waste near the coast.
- Reduces the kinetic energy of the ocean.
- Large footprint TSG farms may reduce sea usage.
The Environmental Impacts of Tidal Power
There are several environmental concerns associated with tidal power. Arguably the most important one refers to the effects of power plants on marine life. Despite the fact that many projects are equipped with safety mechanisms, marine animals may still become entangled in the mechanisms. In addition to this, the constant rotating sound may discourage marine life from inhabiting the area. Here are the main environmental impacts of tidal power, according to technology used:
- Environmental Impact of Tidal Barrages. Installing a barrage will change the shoreline of the estuary or bay, thus affecting the entire ecosystem. In addition to this, inhibiting the flow of water may result in less flushing, which ultimately leads to additional turbidity and decreased levels of salt water. Another concern refers to fish migration. If they are unable to access breeding streams, fish might attempt to pass through the turbines. Other concerns: decreased accessibility for ships, acoustic problems.
- Environmental Impact of Tidal Lagoons. Tidal lagoons have yet to be put into practice, but scientists fear blade strike on fish attempting to access the lagoon as well as changes in the sedimentation process. Because these effects are localized, their effects can be diminished.
- Environmental Impact of Tidal Turbines. The biggest problems with tidal turbines are associated with entanglement of marine wildlife and blade strike. Because turbines are placed in the water, their acoustic effects are far-reaching and can disrupt the life of marine organisms (particularly those who use echolocation for communication). Other concerns: reduced water quality, tidal energy removal and disrupting sedimentation process.
Interesting Tidal Power Facts
Hungry for more information about tidal power? Here are 10 interesting tidal power statistics and facts:
- 300 MW of tidal power are required to power one quarter of Nova Scotia homes.
- 300 MW represents only a fraction of the 2500 MW potential of the Bay of Fundy.
- Nova Scotia has over 450 PhDs in ocean-related disciplines.
- Tidal energy is one of the oldest forms of energy. Tide mills date back to 787 A.D.
- A tide mill consists of a storage pond that is filled by incoming tide with the help of a sluice. The tide mill is emptied during low tide with the help of a water wheel.
- At present there is only one major tidal energy power plant in operation. The La Rance power plant has a capacity of 240 MW.
- Tidal movement patterns can be predicted months, even years in advance, making tidal energy an extremely predictable power source.
- Engineers are working on three tidal energy prototypes: the vertical axis turbine, oscillating devices and horizontal axis turbine.
- Tidal turbines can be anchored to the sea/ocean bed.
- Tidal power facilities also provide secondary benefits such as roads, bridges, or recreational areas.
The Future of Tidal Power
In the world of sustainable energy solutions, tidal power continues to be an abstract notion because it is not as mechanically developed as biomass or hydro-power and because it did not obtain the same sort of press as wind or solar power.
But if tides are so predictable, while wind is so fickle, why is tidal power having such a hard time?
The problem has never been with the tidal movement patterns, but with the aggressive nature of the ocean. Many investors are finding it hard to protect their facilities against infrastructural damage. The only way to avoid this problem is to invest even more money in a technology that is already expensive.
Without a doubt, the future of tidal energy relies on the costs involved. At the moment, the technology used is not advanced enough, but the latest prototypes prove that progress is being made. Thirty years from now, tidal power will blossom into an incredibly sustainable energy technology.
Suggested Read: Tidal Misconceptions, by Donald E. Simanek
Tidal Power Diagrams: