Tidal Power

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Kristina H.

Michelle P.

Contents

What are tides?

Tides are the result of the Earth's ocean surface rising due to the tidal forces of the Sun and Moon acting on the oceans. They begin in the oceans and make their way to the coastlines where they appear to be the regular rise and fall of the sea surface. The Sun and the Moon produce a total of 7 different types of tides that impact tidal power: ebb, spring, neap, high, low, flood, and slack.


While high and low tides refer to the water level, spring and neap tides refer to the alignment of the Sun and Moon. The first picture below shows how spring and neap tides are formed when the Sun and Moon align.


Image:tide.jpg

How tides generate electricity

In order to produce tidal energy, a dam must be built across the opening to a tidal basin, called an estuary. The barrage (the dam), consists of turbines that are positioned within tunnels in the dam. The turbines in the barrage rotate when a tide comes in, thus producing electricity.

Image:tidalpower.gif


There are three ways tides can be harnessed to produce electricity:

  1. Tidal stream systems: use kinetic energy to move water to power turbines, similar to the way windmills use moving air.
  2. Barrages: use potential energy in the difference of high and low tides. Barrages are similar to dams and have the full width of a tidal estuary.
  3. Tidal lagoons, similar to barrages, are constructed as self contained structures.


Here is a video from youtube that shows how tidal power works.

Image:turbine.jpg

This picture shows a turbine farm producing electricity from tidal power.

Pros and Cons of Tidal Power

Pros:

  • Once the dam is built, tidal power is free. This is possible because tidal power harnesses the natural power of tides, instead of consuming fuel. Also, maintenance costs for running a tidal station are usually pretty inexpensive.
  • Tides are considered reliable because high and low tides are easy to predict when they will occur. Twice a day, the tide goes in and out usually at predicted times, making tidal energy easy to maintain.
  • Because nothing is consumed in the rising of tides, tidal energy is renewable. The tides will continue to ebb and flow, so the energy s there for the taking.
  • It produces no waste or greenhouse gases
  • It needs no fuel
  • Produces electricity reliably
  • Tidal power relies only on the gravitational pull of the Sun and Moon.


Cons:

  • The initial costs of building a dam are extremely high. The dam also only provides power for about ten hours a day, when the tide is moving in or out of the basin.
  • Constructing the barrage can affect transportation systems in the water. Because of construction, boats are unable to cross the barrage and commercial ships, used for transport or fishery purposes, are forced to find alternate routes to travel through.
  • The barrage may affect the aquatic ecosystems that live around it.
  • The maximum energy production is only 2.5 terawatts.
  • Tidal energy can only be produced in places where water level changes significantly. Twenty percent of the total potential energy is usually lost and eighty percent of potential energy is usually used for generating electricity.
  • It Only produces power for about 6-12 hours a day.
  • Water Pollution

How popular is tidal power when it comes to electricity?

According to an analysis conducting by the Electric Power Research Institute, tidal power produces up to ten percent of the electricity the United States consumes.


In order to produce tidal power, locations for turbines have to be chosen carefully. Tidal stream systems are usually in areas where fast currents and natural flows exist. Examples of such areas are entrances to bays and rivers, headlands, between islands, or around rocky points. In the United States only three states have so far been able to provide such locations: Alaska, California, and Maine.

Potential sites for the future:

  • Cook Inlet in Alaska
  • Pentland Firth in Scotland
  • Dee estuary in Wales
  • Pembrokeshire in Wales
  • River Severn between Wales and England
  • Solway estuary (Morecambe Bay) in England
  • Humber estuary in England
  • Mersey river in England
  • Channel Islands in the English Channel, off the French coast
  • Cook Strait in New Zealand
  • Kaipara Harbour, New Zealand
  • Strait of Gibraltar
  • Bosporus in Turkey
  • Bass Strait in Australia
  • Torres Strait in Australia
  • Strait of Malacca between Indonesia and Singapore
  • Bay of Fundy in Canada.
  • East Riverin New York City
  • Vancouver Island in Canada
  • Strait of Magellan south of mainland Chile
  • Golden Gate in the San Francisco Bay
  • Piscataqua River in New Hampshire
  • The Race of Alderney and The Swinge in the Channel Islands
  • San Jose, Argentina
  • Mezen, Russia
  • Mozambique Channel in South Africa


Tidal Power only accounts for a small percentage of the world's generated power. It is somewhere around 20% of the power.

Tidal Power is considered a renewable energy source because the Earth's tides are caused by the tidal forces due to gravitational interaction with the Moon and Sun, and the Earth's rotation, tidal power is practically inexhaustible.

Current Events

  • Here is a video from New York Times that is about tidal power in the East River. [1]
  • "Saudi Arabia of tidal power' woos dozens of energy firms"

Many energy companies all across the world are hoping to install green'energy devices all across the seas of North Scotland. All the companies participating are hoping to place dozens or even hundreds of these tidal turbines and other devices up. "The Scotsman" Published Date: 12 February 2009 By Jenny Haworth

  • "Marine Current Turbines Installs Tidal Energy Turbines on Vancouver Island"

The MCt, in 2007, hoped to install at least three of the 1.2 megawatttidal energy turbines by 2009 in Vancouver Island's Campbell River. This is just the first step of a bigger plan. Seagen is the first and only tidal device ready for deployment in the world. They have the materials needed and it will also provide many jobs and power that will be predicatable. November 9, 2007 British Columbia, Canada [RenewableEnergyAccess.com]

  • "US Researchers Hope to Tap Ocean Flows for Electricity"

Off the soast of Florida, researchers hoped to test underwater turbin systems for producing energy. They believe that the same energy that drives waves andcurrents can produce electrical power. They want to make a Turbine farm off the Key West coast. By the end of 2008, early 2009, they hoped to have several turbines up to see how they worked as a group. THye hope to learn form them and maybe one day share them with the world. By Brian Wagner Key West, Florida 06 March 2008

  • "Lancaster Launch for Northwest Tidal Energy Group"

On the 17th of December in 2008 the Lancaster University launched a group to study tidal energy potential within Englands Northwest Coast. December 2008

Key Terms

  • Barrage: Similar to a dam.


  • Ebb tide: The period when the water level is falling. This period is usually after the high tide, but before the low tide.


  • Flood tide: The period when the water level is rising. This period is usually after low tide, but before high tide.


  • High tide: When the largest increase in water level takes place.


  • Low tide: When the largest decrease in water level takes place.


  • Neap tides: A period that occurs usually every two weeks when the Sun and Moon are at a 90 degree angle to each other. Neap tides produce a minimum tidal range and only occur during the first and third quarter moons.


  • Period: A time interval between two events, such as two high tides in the same area.


  • Slack tide: A period where the water level is neither rising or falling.


  • Spring tides: A period where the tidal range reaches the maximum. Spring tides occur every two weeks when the Sun and Moon are in line with each other, during the new and full moons.


  • Tidal current: A horizontal movement of the water due to tidal forces.


  • Tidal range: The vertical distance between the high and low tides during a single tidal cycle.


  • Turbine: A rotary power-generating device driven by a moving fluid, such as

water, steam, gas, or wind, that converts kinetic energy into mechanical energy.

Lesson Plans

Questions:

  1. What are the seven types of tides that can impact tidal energy?
  2. After looking at the pro's and con's list do you feel that tidal power is more benifitial to us or not?
  3. Explain briefly how tides can generate power.
  4. Explain why tidal power is considered a renewable source of energy.
  • This came from Filamentality. It has some sites that you can go to that provides easy diagrams for kids to follow and understand tidal energy.

[2]

  • This was one of two sites on another filamentality site and it has vidos your kids can watch and also informtaion you can use in your lessons.

[3]

  • This was the other onethat came from that site and it has information on the differnet typed of tidal energy.

[4]

  • This came off off filimantility and is an internet activity where your students can gane an understnading and more knowledge from the sites that they give on energy and tidal energy.

[5]

  • This is suppose to give your students a better understanding of how tidal energy is generated and how it works.

[6]

  • This is a lesson planon Ocean Energy and some other forms of it.

[7]

References

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