Comment & Debate
Tidal energy utilizes the flow and energy of the tides and currents to generate electricity. Because the tides and currents are driven largely by the gravitational pull of the moon, tidal energy is actually a form of exploiting lunar gravitational energy. There are different general categories of tidal power, although they both exploit the same basic tidal-lunar forces: tidal stream generators and barage tidal energy. Tidal stream generators are akin to wind turbine technology. They capture both the incoming and outgoing “stream” energy of tides, similar to how wind turbines capture wind energy. Barage tidal energy is much like dam hydroelectric technology. It involves building a barrage across a bay or an estuary to force tidal water through turbines situated in the barage. The debate surrounding tidal energy is mainly about analyzing the pros and cons of this technology, and comparing them with the pros and cons of the various other “green” energy alternatives such as “clean coal”, natural gas, wind energy, solar, geothermal, nuclear, hydroelectricity, and biofuels. The purpose of this debate is to determine whether tidal energy should be a significant part of national and global energy and global warming plans, and whether it should receive government funding and private investments. The debate revolves around numerous questions. For the purpose of fighting global warming, will tidal power deliver a strong return on investment? Is it truly “green”? Are there any significant costs to marine wildlife? What are the economic benefits and costs? Is tidal technology sufficiently developed or is it too new? Is it cheap enough to install and maintain? Will the energy produced provide a good return on investment? What are the specific pros and cons of tidal stream generators and barage tidal energy systems?
“The few studies that have been undertaken to date to identify the environmental impacts of a tidal power scheme have determined that each specific site is different and the impacts depend greatly upon local geography.” It is important, therefore, to judge the potential for tidal energy on a case by case basis.
Many forms of energy have potential environmental impacts. The focus should be on designing regulations that minimize or eliminate these impacts.
“It has been estimated that in the Bay of Fundy, tidal power plants could decrease local tides by 15 cm. This does not seem like much when one considers that natural variations such as winds can change the level of the tides by several metres.”
Barrages can help protect coastal ecosystems from the devastation of a storm. This protective purpose more than adequately makes-up for any of the minor damage that tidal energy may do to marine ecosystems.
Offshore turbines do not alter the flow of tides as much as barrages can, so have a smaller environmental impact.
Barrages effectively dam estuaries and bays in order to build-up and concentrate water mass into turbines that convert the energy to electricity. Daming a bay or estuary in this way changes tidal flows, which can have significant consequences for aquatic and shoreline ecosystems, including changing the flow-dynamics of an marine ecosystem, disorienting animals that depend on the flow dynamics of an ecosystem, increasing silt build-up, killing marine wildlife (particularly fish populations), and destabilizing ecosystems that depend on that marine wildlife.[1]
Bays and estuaries are always naturally “flushed” or cleansed and replenished by tide-waters flowing in and out. To the extent that tidal energy impairs the natural flows of these tides, it impairs this natural “flushing” mechanism. This can alter and even destroy an ecosystem.
Tidal energy can slow the movement of water in a bay or estuary, which reduces the amount of kinetic energy and causes the body of water to freeze-over more often or for longer periods of time. This has consequences for marine ecosystems.
“The devices’ anchors and cables might damage critical ecosystems like salt marshes, estuaries, and near-shore reefs, or alter the natural processes that maintain ocean and coastal ecosystems, such as the movement of sand, silt, animals, and larvae.”
Tidal power derives its power from the ocean tides and currents. Because it does not burn fossil fuels to obtain energy, it emits no greenhouse gases or air-borne pollutants. As such, tidal energy can act as an important substitute for fossil-fuel energy, removing greenhouse-gas polluters from operation.
Tidal energy can produce massive quantities of energy. And, because tidal energy is clean, it can replace fossil fuels and substantially reduce greenhouse gas emissions. According to one source, a single tidal barrage can prevent the release of approximately one million tons of CO2 per TWH generated.[2]
“Tidal energy use may not be a big player in our energy future, but it can make a contribution.” By some estimates, tidal power can contribute to 6% of human electricity needs. That’s great. Any 0-emission contribution should be welcome and encouraged.
“there is only one major tidal generating station in operation. This is a 240 megawatt (1 megawatt = 1 MW = 1 million watts) at the mouth of the La Rance river estuary on the northern coast of France (a large coal or nuclear power plant generates about 1,000 MW of electricity).”
The fact that individual tidal energy plants produce so little energy combines unfavorably with the fact that there are very few regions in the world that are suitable for tidal energy. Obviously, this combination means that tidal power’s cumulative energy production (and potential) is very small comparatively. If tidal energy is incapable of generating significant quantities of energy, it is unviable as a “clean” substitute for fossil fuels. It will reduce greenhouse emissions by a negligible degree and will have effectively no positive impact in the fight against global warming.
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