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Sihwa Barrage Plant
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Tidal Plant Off Maine
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The gravitational pull of the moon and sun along with the rotation of the earth cause the tides. In some places, tides cause water levels near the shore to vary up to 40 feet. People had harnessed this movement of water to operate grain mills more than a 1,000 years ago in Europe. Today, tidal energy systems generate electricity.  Several tidal power barrages operate around the world. The Sihwa Lake Tidal Power Station in South Korea

has the largest electricity generation capacity at 254 Megawatts (MW). The oldest operating tidal power plant is in La Rance, France, with 240 MW of electricity generation capacity. The next largest tidal power plant is in Annapolis Royal in Nova Scotia, Canada, with 20 MW of electricity generation capacity. China, Russia, and South Korea all have smaller tidal power plants.

The barrage is installed across an inlet of an ocean bay or lagoon that forms a tidal basin. Sluice gates on the barrage control water levels and flow rates to allow the tidal basin to fill on the incoming high tides and to empty through an electricity turbine system on the outgoing ebb tide. A two-way tidal power system generates electricity from both the incoming and outgoing tides.

A potential disadvantage of tidal power is the effect a tidal station can have on plants and animals in estuaries of the tidal basin. Tidal barrages can change the tidal level in the basin and increase turbidity (the amount of matter in suspension in the water). They can also affect navigation and recreation.

The United States does has only one tidal power plant and has very few sites where tidal energy could be economical to produce. France, England, Canada, and Russia have much more potential to use tidal power.

Wave Power Station
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Tidal Turbine Canada
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Tidal turbines look similar to wind turbines. They can be placed on the sea bed where there is strong tidal flow. Because water is about 800 times denser than air, tidal turbines have to be much sturdier and heavier than wind turbines. Tidal turbines are more expensive to build than wind turbines, but capture more energy with the same size blades. Strangford Lough, Scotland, and Uldolmok, South Korea, both have 1.5 MW tidal turbines. A tidal turbine project is under development in the East River of New York. Another project with up to 400 MW of electricity generation capacity is under development in northern Scotland.

The scientists analyzed 139 countries for which data was publicly available from the International Energy Agency. These 139 collectively emit more than 99 percent of the global warming gas carbon dioxide worldwide.

We have to do better if we are to provide alternative power for our burgeoning population

Energy Consumption    Per Country — Per Head………Wikipedia

They analyzed what raw renewable energy resources were available to each country, and investigated what each needed to electrify their transportation, heating, cooling, industrial, agricultural, forestry and fishing sectors.The researchers calculate that these 139 countries could be powered 80 percent by clean, renewable energy by 2030 and 100 % by 2050.                        Click to Enlarge    The mix of resources they envision for the goal include the following estimates.

• 21.36 percent from photovoltaic solar plants
• 9.72 percent from concentrated solar plants
• 14.89 percent from residential rooftop solar
• 11.58 percent from commercial and government rooftop solar
• 23.52 percent from onshore wind
• 13.62 percent from offshore wind
• 4 percent from hydroelectric energy
• 0.58 percent from wave energy
• 0.67 percent from geothermal energy
• 06 percent from tidal turbine energy

Why such low use of Ocean Energy?

1. Siting: Suitable sites for tidal power plants must meet specific requirements. For example, sites must have a tidal range of at least (about 23 feet). Current technology also limits the suitable geographic location of tidal energy plants. The U.S. has only a handful of sites appropriate for an economically competitive commercial plant. A study conducted by the U.S. Department of Energy, estimated that the U.S. (excluding Hawaii and Alaska) could generate only 0.6 Terawatt hours (TWh) of the 4000 TWh needed each year.
2. Intermittent: Tidal energy can only be produce electricity during tidal surges, limiting electricity generation to 10 hours per day.
3. Environmental impact remains unknown:Tidal energy is still in its infancy. Therefore, the environmental effects of tidal energy plants have not been fully studied. For example, tidal barrages rely on manipulation of ocean levels and therefore pose similar environmental effects of hydroelectric dams.
4. Expensive:Technology for generating electricity from tidal energy is relatively new and not yet commercially profitable. Tidal power plants are also expensive to build and maintain. There are very few commercial tidal energy plants operating in the world. Therefore, advances in technology and construction at a larger scale are needed to lower the LCOE of tidal energy.