Tidal energy or tidal power is a form of hydropower that uses the kinetic energy of the tides to spin an underwater turbine and generate clean electricity.
Tidal energy is part of the alternative energy sources and is also considered a renewable energy source because the energy of the tides is continuous. Let’s see what are the advantages and disadvantages of tidal power.
Tidal Power Definition
The energy of the tides is mostly produced by the gravitational forces of the Sun and Moon applied to our oceans.
When the gravity of the Earth and the Moon are aligned with each other the gravitational forces of these two celestial bodies are getting strong enough to move a very large volume of water in our oceans towards the shore creating the “high tide”.
Also, when the gravity of the Moon and Earth are at an angle of 90 o to each other, their gravitational forces are weaker, so the large volume of water in our oceans will flow back in its initial position and away from the shore, creating the “low tide”.
A tidal cycle is formed by a high tide followed by a low tide.
Two high tides and two low tides every day
Every coastal area of the planet receives two high tides and two low tides every day, which represents a time period of 24 hours and 50 minutes here on Earth.
When the Moon gets in perfect alignment with our planet and the Sun, the gravitational forces of the Moon and Sun combined will generate a very high tide and a very low tide in a tidal cycle.
These powerful tides are called spring tides (maximum), and they usually occur during the new moon and during the full moon phase.
When the gravitational forces of the Moon and Sun are against each other, the tides will be very low, and will be called neap tides (minimum).
The weak tides are creating a very small difference between the high and the low tide in the same tidal cycle.
Even if we have two tidal cycles every lunar day (24 hours and 50 minutes), we can say that tidal energy is a predictable source of power, so tidal energy can be considered a renewable energy source that is predictable and regular, not an intermittent source of clean energy such as solar and wind power.
How Does Tidal Power Generate Clean Electricity?
Being a predictable and regular source of clean power, tidal energy can be used to generate clean electricity.
The turbines used to transform the kinetic energy of the tides into clean electricity using generators are almost similar with the turbines used to produce hydropower.
The only difference is represented by the fact that the turbines used to produce clean electricity from tidal energy can spin in both directions (forward and backward) because the tides are moving forward at high tide and backward at low tide.
This type of turbines will use reversible electrical generators, which are more expensive than the single direction generators.
The shape of the turbine can be also different because some modern tidal turbines have no central rotor in order to protect marine life.
Systems Used Today to Harness Tidal Energy
Tidal power plants can be installed only along coastlines because coastlines receive two high tides and two low tides every day.
There are several systems used to harness the power of the tides today, such as: tidal turbines, tidal barrages and tidal fences.
1. Tidal Turbines
Tidal turbines look like wind turbines, but more robust because they need to work in strong sea currents.
The blades of the turbine will be shorter and stronger, and as I mentioned earlier, the turbine must spin in both directions forward and backward, so the generators used to turn the kinetic energy of the tides into clean electricity will be reversible electrical generators.
Modern tidal turbines will have the central rotor removed to protect marine life that can be caught by the rotor and the rotating blades of the underwater turbine.
With the central rotor removed, marine life has a corridor through which can get out and escape from the rotating turbine.
2. Tidal Barrages
A tidal barrage is a dam that utilizes the potential energy generated by the change in height between the high and the low tides. The difference between the low and the high tide (tidal range) must be at least 7 meters.
This energy is used to spin a turbine that produces clean electricity with the help of the reversible electrical generators.
Tidal barrages are usually installed across bays and estuaries, and today there are several tidal barrages already installed or in under development (in Russia, France, Canada, China and South Korea).
3. Tidal Fences
Tidal fences use vertical or horizontal turbines that operate in strong sea currents to produce clean electricity.
Tidal fences can be found between a tidal barrage and a tidal turbine stream system.
Ocean water is 832 times more dense than air, so the turbines used to harness tidal energy must be more robust than the turbines used to produce wind power.
Because the sea currents are very strong and the water is much denser than air, the sea currents will apply a much stronger force on the turbines, so the power produced will be greater.
Tidal energy has many advantages as a renewable energy source, but also a few disadvantages.
Advantages of Tidal Power
There are several advantages produced by tidal power as a renewable energy source.
1. Is A Renewable Energy Source
Due to the fact that the high and low tides are created by the gravitational forces of the Moon and Sun we can say that tidal energy represents an infinite resource of clean energy.
2. Is A Predictable Source Of Clean Energy
Because there are two tidal cycles in a lunar day (24 hours and 50 minutes) and the level of the high and low tides are predictable, we can say that tidal energy is a known source of clean electricity ideal for the electrical grid.
3. Has A Low Visual Impact
Being located under water, the systems used to harness the power of the tides have a very low visual impact.
4. Can Reduce Our Dependence On Fossil Fuels
Tidal energy produces clean electricity without releasing greenhouse gases, so it is considered an ideal source of power that can reduce our dependence on fossil fuels such as coal, oil and natural gas.
5. Produces Only Low Noise Pollution
The systems used to harness tidal energy are submerged and the noise pollution produced under water is low.
6. Tidal Barrages Provide Protection Against Flooding
Tidal barrages are usually built across bays and estuaries and can provide protection against floods and can protect the land from the damages caused by the sea.
7. Has A Great Potential To Generate Clean Electricity
Because all the coastal areas of the planet receive tidal cycles during a lunar day (24 hours and 50 minutes), there is a great potential to produce free and clean electricity from tidal energy on planet Earth.
8. Is Cost-competitive
Once installed on the sea, the systems used to harness the power of the tides are cost-competitive with the other sources of energy on the market.
Even if the initial investment with the tidal project is pretty high, the entire investment will be recovered in the long run.
9. Tidal Barrages Provide Protection For Coastal Areas And Naval Ports
Tidal barrages are dams that can provide protection for coastal areas and naval ports against dangerous tides produced by bad weather and heavy storms.
Disadvantages of Tidal Power
Like any other source of energy, tidal power has its own drawbacks.
1. High Initial Costs
Being a new and innovative technology, the initial costs of the systems used to harness tidal energy are pretty high.
However, experts predict that by the year 2020, the systems used to produce clean electricity from tidal energy will become much more affordable.
2. Has An Impact On Marine Life
Tidal barrages are considered to have the same impact on the environment as hydroelectric dams.
In addition, the turbines used to generate clean electricity can kill marine life.
However, the new turbines used to harness tidal energy have no central rotor, so marine life has an escaping corridor through which it can escape the rotating turbine.
3. The Initial Investment Can Only Be Recovered In A Long Time
Any new technology is expensive in its first years, and this is the case of the technology used to produce clean electricity from tidal power.
The initial costs with the production and the installation of a new system used to harness tidal power can be so high that even if the operational costs of the tidal power plant will be minimal, the period of time required to recover the initial investment will be pretty long.
4. Requires Certain Conditions To Work Properly
Tidal energy cannot be harnessed everywhere on the planet, the today’s technology used to produce clean electricity using the tides requires a coastal area where the tides and the tidal streams are strong all the time.
Final conclusion
Tidal energy is relatively new on the energy market today, and because the systems used to harness the great potential for free and clean electricity of the tides are still expensive, we need to wait a few more years to see a wide spread of this renewable energy source in the coastal areas of the planet.
Hi, Our Variable Pitch Wind Turbines (VAWT) which we have been developing for 10 years would be ideal for tidal environment. With the mass being 76 times higher than air it is obvious far more torque can be produced.
It would be exciting to start some tests in the near future.
Taking advantage of our very efficient design and a much lower and longer design profile than normal Horizontal Axis Wind Turbines (HAWT) types. Our VAWT can be mounted horizontally or vertically.
A wind turbine cannot survive in strong sea currents, that’s why the turbines used to harness the power of the tides are much more robust and expensive.
While tidal energy is a predictable source of energy, it is not a constant source. Tidal currents stop for several hours at both high tide and at low tide before changing direction. During those periods of slack tide, you will not be generating any electricity at all.
If slack tide occurs at the time of peak demand, you will still need another source of generating electricity to cover the load. Just because it’s predictable doesn’t mean you don’t have the same problems you do with solar and wind in needing redundancy.
That’s true, tidal energy is not a constant source of power, it is only a predictable one because we have two tidal cycles per day, and there are a few hours per day when the tides are not strong enough to generate electricity.