By Sait Sarr Graduate Student Kentucky State University Tidal energy By Sait Sarr Graduate Student Kentucky State University

INTRODUCTION Tidal energy, also called Tidal or Hydrokinetic Power, is a form of hydropower that converts the energy of tides into useful forms of power, mainly electricity. In this research study, I discussed the generation of tidal energy, the specific areas tidal energy has taken place, its pros and cons, environmental concerns with harnessing tidal power and its future as a renewable energy source. The different techniques in harnessing tidal energy are also discussed in detail with examples. Although not yet widely used, tidal power has potential for future electricity generation. 

TIDAL POWER GENERATION The basic techniques with the harnessing of tidal power are to block estuaries with a barrier, and force the water to flow through turbines to generate electricity. Figure 1- Principle of tidal power generation One could also couple a dam and storage basin for water. When the tide rises, the dam is open and sea water fills the basin. The dam is closed when the tide goes down, and the water contained in the basin can be released to flow through a turbine to produce electricity.

TIDAL POWER GENERATION The most expensive part of a tidal power plant is the dam (Ngo and Natowitz, 2009). Its price is proportional to its length L. In order to be economically competitive, the rule of thumb is that the length-to-area ratio of the dam, L/A, should be smaller than 80. Tidal power can be classified into four generating methods- Tidal Stream Generators, Tidal barrage, Tidal Lagoon and Dynamic Tidal Power.

TIDAL STREAM GENERATORS Tidal stream generators (or TSGs) make use of the kinetic energy of moving water to power turbines, in a similar way to wind turbines that use wind to power turbines. Some tidal generators can be built into the structures of existing bridges. Figure 2 - Picture of SeaGen Land constrictions such as straits or inlets can create high velocities at specific sites, which can be captured with the use of turbines. These turbines can be horizontal, vertical, open, or ducted. Figure 2 above is the world's first commercial-scale and grid-connected tidal stream generator – SeaGen – in Strangford Loug, Northern Ireland.

TIDAL BARRAGE Tidal barrages make use of the potential energy in the difference in height (or hydraulic head) between high and low tides. The potential energy from a tide is seized through strategic placement of specialized dams. The temporary increase in tidal power is channeled into a large basin behind the dam, holding a large amount of potential energy. This energy is then converted into mechanical energy as the water is released through large turbines that create power through the use of generators. Figure 3- La Rance Tidal barrage, France. Barrages are essentially dams across the full width of a tidal estuary. An example would be the La Rance Tidal barrage in France as seen above. It has a power of 240MW and produces 500GWh of electricity yearly. . A dam 330 meters long was build in front of a 22 square kilometer basin. The tidal range (the difference between high and low tides) averages 8 meters and reach up to 13.5 meters.

TIDAL LAGOON A newer tidal energy design option is to construct circular retaining walls embedded with turbines that can capture the potential energy of tides. The created reservoirs are similar to those of tidal barrages, except that the location is artificial and does not contain a preexisting ecosystem.  Figure 4- The Swansea Bay Tidal Lagoon  The Tidal Lagoon Swansea Bay development, seen in figure 4 above, is proposing to create a 250MW power plant that will be an extremely reliable electricity source offering predictable zero carbon electricity for 120 years. The project has the potential to power 155,000 U.K homes, saving 236,000 tons of carbon emissions a year.

DYNAMIC TIDAL pOWERs Dynamic tidal power (or DTP) is an untried but promising technology that would exploit an interaction between potential and kinetic energies in tidal flows. It proposes that very long dams (for example: 30–50 km length) be built from coasts straight out into the sea. Tidal phase differences are introduced across the dam, leading to a significant water-level differential in shallow coastal seas. The main advantage of dynamic tidal power is that a single installation could produce anywhere from 8 to 15 giga-watts of power, orders of magnitude more than any other tidal energy system.

THE PROS OF TIDAL ENERGY Consistent Power - Tides move constantly throughout the day, which provides a consistent stream of electricity generation capacity. Tidal currents are highly predictable.  Pollution-Free - By taking advantage of only the tide, tidal power creates no greenhouse gas emissions or water pollutants. Tidal power is environmentally friendly. Low Operating Costs - Once installed there are few operating costs or labor costs, unless there is a device breakdown. Renewable - No material resources are used or changed in the production of tidal power, making it a truly renewable power. Efficient - Tidal Power converts roughly 80% of the kinetic energy into electricity, as opposed to coal and oil which convert only 30% of the energy held within.

THE CONS OF TIDAL ENERGY Environmental Effects- The barriers can prevent fish and boats from travelling through. The habitat of some birds can be destroyed, and the accumulation of sediments can reduce the volume of the reservoir. Sea life could be harmed by the blades of the open water turbines. High Initial Costs - The high cost of the different Tidal Stream Generators and cost of installing power lines underwater could lengthen the payback period and be cost prohibitive. Locations- Good locations are not so frequent. Shifting Tides - Changes in tidal movement could substantially reduce efficiency of TSGs. Device Breakdown - Strong ocean storms and salt water corrosion can damage the devices, which could increase the cost of construction to increase durability.

ENVIRONMENTAL EFFECTS The environmental impacts of Tidal energy is very minimal compared to other sources of energy, especially fossil fuels. It is an environmentally-friendly energy source. Tidal power creates no greenhouse gas emissions or water pollutants There is a non-negligible environmental impact on the coastline (Ngo and Natowitz, 2009). The barriers can prevent fish and boats from travelling through. The habitat of some birds can be destroyed, and the accumulation of sediments can reduce the volume of the reservoir. Sea life could be harmed by the blades in the open turbines.

The present & future of tidal energy Newer technology and a fuller, more systematic understanding of estuaries and streams has put tidal power in a position to become one of the most reliable forms of renewable energy (Henderson, 2013). Systems like dynamic tidal power, tidal stream generation, and other new technologies will probably be utilized as energy needs increase and fossil fuel use becomes less desirable. Truly, the future of tidal energy is tightly hinged to the costs involved. The future looks brighter today than ever before.

CONCLUSION Tidal energy should be focused on for the next alternative fuel sources as it is a renewable energy source with many potential benefits. There are many sites worldwide that can use the barrage and open water turbine processes. These turbines show a lot of potential, and reduce some of the costs and environmental risks associated with tidal power usage. Tidal power cannot support all of our energy demands, but it will be a valuable source of renewable energy. If developed correctly, tidal power can become the primary provider for our future energy requirements.

works Cited https://en.wikipedia.org/wiki/Tidal_power retrieved November 10, 2015.   http://greenthefuture.com/TIDALPOWER_PROSCONS.html retrieved Nov. 12, 2015. http://jrscience.wcp.muohio.edu/fieldcourses04/PapersMarineEcologyArticles/Fi nalPaperonTheProcessofM.html retrieved November 8, 2015. http://www.reuk.co.uk/La-Rance-Tidal-Power-Plant.htm retrieved November 8, 2015. Henderson, M. (2013). The Present and future of Tidal energy. Environmental and Energy Management News, April 2013. Ngo, C. and Natowitz, J. (2009). Our Energy Future: resources, alternatives and the environment (p.138-140). John Wiley & Sons, Inc. (2009).

Thank you! Questions???