There is evidence that people began harnessing the power of the tides before 900 CE. The principle is simple and obvious. Set a dam to capture water at high tide and hold it. When the tide is low, run the water through a sluice gate to drive a water wheel. Use the water wheel to power machinery, usually a flour mill.
It is an obvious step from this use to electrical generation, but there are important tidal energy pros and cons to take into account. Here we will explain the primary tidal energy benefits and disadvantages.
Tidal Energy Pros and Cons
Tidal Flow Is Reliable and Predictable
Unlike the weather patterns that decide the success of solar and wind power generation, the tides are well understood and regular. Almost twelve and a half hours after the last high tide, we know that the tide will be high again.
The Cost of Electric Generation Is Low
Since the movement of the moon and sun drive the tides, we don’t need fuel to generate electricity by tidal power. The only ongoing cost in operation is for maintenance. The Rance Tidal Power Station in France produces electricity at a cost of only 3.7 cents/kWh, less than half of coal power plants in the area. The only type of electric generation that costs less to run is hydro-electric (at dams and waterfalls).
This Is Known Technology
We can certainly expect improvements to the current designs, but the Rance Power Station has been in continuous operation since 1966. The Rance installation supplies the French power grid with about 600 GWh every year. Specialists anticipate that these power plants will have a long operational life as compared to other power plants, with a lifespan of 100 years or more.
The Impact on Wildlife Is Minimum
Tidal stream generators are similar in concept to wind generators, harvesting tidal flow underwater. Because water is well over 750 times as dense as air, tidal stream generators can use smaller and slower rotors than wind turbines use. This presents little danger to marine life, making them safer to animal life than other green energy generation methods.
Barrage tidal systems, such as used at Rance, are essentially dams with turbines attached. They present no more danger to wildlife than other dams do.
Minimal Greenhouse Gas Emissions
The only greenhouse gasses produced by tidal energy generation is during construction. This can be a large amount, because of the amount of concrete used in building a barrage tidal system. Averaged out over the lifespan of the system, it is still a far smaller carbon footprint than produced by even the cleanest fossil-fuel power plants.
There Can Be Significant Ecological Impacts
A barrage tidal system has a significant impact on local habitat. It affects the size and shape of the intertidal zone; the area that is submerged at most high tides and submerged during most low tides. It also alters the salinity of local water, and can cause silting in the river system it is built on.
This can make the area less desirable to some species. In spite of this, the local ecology is likely to find a new balance, and may attract new species. This could be considered a mixture of tidal energy pros and cons. Construction of any type of tidal energy installation is likely to disrupt the local habitat during installation.
The Cost of Construction Is High
A tidal energy installation is among the most expensive to build, on a capacity/dollar basis. The low operating costs and expected lifespan of the installation balance this out. However, investors do not often want to wait so long before they start to see a return on their investment. An improvement in methods or a breakthrough in technology could this problem.
Tidal Energy Depends Upon Geography
It is obvious that tidal energy must be installed at the coast of a body of water large enough to have tides. What is less obvious is that not all ocean coasts are suitable. A tidal barrage installation must have a 5 meter range between low and high tides to operate effectively. A tidal stream system must have a reliable flow rate of 3.9 knots (2 meters/second) for effective generation. Location is a deciding factor in tidal energy pros and cons.
Tidal Generation Is Not Constant
Depending on design, a tidal barrage generation system produces electricity about 12 hours per day. A tidal stream system operates for about 20 hours per day, being unusable at high and low tide. This means that an alternative power source or a power storage system must be available to meet the needs of the grid when using tidal energy.
Tidal Stream Systems Are Vulnerable to Weather
The high density of water that makes undersea turbines more efficient than wind turbines makes these turbines more sensitive to storms, as well. After a heavy storm, transmission lines can be down for a week, or even two weeks. If tide-based generators are damaged by a hurricane or tsunami, the people who depend on them could be without electricity for months longer than that.
Humans have harnessed the tides for many centuries, but electrical generation from tides is a relatively new idea. There is enough kinetic energy in our oceans to supply all of mankind’s electrical desires thousands of times over, once we learn to harness it. More people should learn more about tidal energy pros and cons.
Nearly free electricity with no pollution and minimal damage to the environment is certainly a dream that we can strive for. Spread the idea to your friends, and help build a movement to encourage research into this. Tidal energy pros and cons could be balanced to our long-term benefit with more research and experience. Get involved, and help us spread the word about this option.