By: James Bascom
Given the prevalence of climate change on the debate stage lately, national governments are looking for solutions to reduce greenhouse emissions wherever they can be found. One of the most common solutions comes in the form of transitioning from fossil fuel dependency to the reliance of greener and more sustainable sources of energy. New methods of harnessing renewable energy are gaining popularity around the world. The purpose of this article will be to highlight some of the less common forms of green energy producing technology that have entered the stage and explain just exactly how they work, with a focus on tidal energy.
A type of green energy that has yet to reach the mainstream is the tidal turbine. Tidal turbines work by harnessing the kinetic energy of water generated from shifting tides. The amount of energy produced is dependent on the difference in sea level at the tides’ highest point compared to its lowest point. A tidal turbine generally looks and operates similarly to a wind turbine one might see while driving through the country, only anchored to the ocean floor. However, there are distinct differences in designs. Due to the significantly higher density of water compared to air, the tidal turbine must be sturdier than a wind turbine in both material and construction. While this does generate an extra cost in the manufacturing of the turbine, the additional density allows for the tidal turbines to generate electricity at slower speeds than its terrestrial counterpart. For reference, a tidal turbine can begin generating electricity when facing a current moving at a speed of 2.2 mph. Comparatively, a typical wind turbine requires wind speeds of 7-9 mph. Furthermore, tidal turbines allow for a more consistent power supply compared to wind turbines as tide changes remain inherently predictable, especially when compared to wind patterns.
Harnessing energy from the ebb and flow of tides via tidal turbines is still rather new and has not seen much development. While that is a shame, there is a silver lining. Because tidal energy as a whole is still considered in its infancy, there is a great deal of room for innovation. Just last year the company SIMEC Atlantis Energy unveiled its new turbine design, touted as the largest tidal turbine in the world and generating around 2 megawatts of tidal power. For context, when one of the first wind farms began producing energy in 1980, the 20 turbines it utilized produced 30 kilowatt hours each.
Tidal energy is a bit more costly than harvesting energy with other, more widely established technologies such as wind. Construction has only begun in locations where turbines can be easily planted on the seafloor, and where they would experience large tidal shifts throughout the day. One of the prime locations for tidal turbines is in Scotland with the MeyGen Array, which is the world’s largest array of tidal turbines and is scheduled to supply power to 175,000 homes upon completion. Another large installation is the Sihwa Lake tidal power station in South Korea, which generates about 552.7 gigawatt hours (GWh) annually and utilizes a mixture of tidal barrages and turbines. There is a demonstration in the East River of New York City that will help to bring this type of renewable energy to the United States.
As tidal energy is still early in development, not much is known about its impacts on the environment and local wildlife. In general, research has been inconclusive when it comes to the impacts of this technology on marine life. However, concerns about wildlife colliding with spinning blades have caused companies like SIMEC Atlantis Energy to equip some of their turbines with technology to assess their interactions with marine life.
Continuing in the vein of tidal energy we come to the renewable energy generator known as the tidal barrage. A tidal barrage is a dam like structure that controls the inflow and outflow of water via sluice gates while simultaneously harnessing energy through a turbine placed in between its openings or near the barrage itself. Barrages have been around for awhile, with one of the first major ones constructed in 1966. These structures serve one major purpose, and that is to generate electricity while simultaneously acting as a dam by impeding the flow of water. While this is beneficial in that it can reduce flooding in lowland areas, it is also detrimental to the environment and natural flow of the water. Additionally, barrages are known to alter the flow of saltwater to and from estuaries, meaning that marine life can wind up displaced.
The tidal fence is another form of tidal energy generator and is less harmful to the environment than its larger, tidal barrage counterpart. The reduced harm comes from the inherent less disruptive nature of the fence. While a tidal barrage is reliant on the gates that it uses to block and open the flow of water, the tidal fence allows for the surrounding water to rise and fall with the tide. Tidal fences generally utilize a series of vertical turbines, although designs for fences do vary. By not disrupting the natural ebb and flow of water, the tidal fence allows for fish and marine life to freely pass through. Additionally, as it is not directing and limiting the flow of water as much as a tidal barrage, the tidal fence can be seen as having a reduced impact on water levels along the body of water.
Just as with tidal turbines, there are limitations to the locations in which tidal fences can be constructed. One such limitation is that tidal fences must be constructed in relatively shallow waters, as a portion of the structure must remain above water. Tidal fences are typically built across channels or estuaries and bays. These locations provide steady access to the changing tides necessary to generate electricity, and are also typically shallow. By limiting the location to shallow waters, the tidal fence does remain more obtrusive to the natural flow of water and animals than tidal turbines. That being said, it is significantly less halting to this flow than its barrage predecessor.
Tidal energy is still a relatively new enterprise, with design innovations for energy harvesters popping up regularly. The science of the long term effects on the environment from these kinds of technology is still undetermined. One thing is certain, tidal power is a promising energy source that can expect to see development and innovation for years to come.
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