1. Hydroelectricity

2. Where does it come from? Hydroelectricity comes from dams which are built on rivers. Rivers provide kinetic energy. Kinetic energy comes from gravitational potential energy which is available in glaciers up the mountain which melt when heated and form rivers. Dams trap water, building up gravitational potential energy. When dam release water, the water turns turbines that generate electricity. Hydroelectricity can also come from tidal waves which is another clean source of energy which has less disadvantages than dams, like wind turbines which can be placed in oceans to generate clean and renewable sources of energy. There is a picture of this power generator below.

3. Explanation A hydroelectric dam produces hydroelectricity for power. Hydroelectric dams produce hydroelectricity when gravitational potential energy becomes kinetic energy. (When water from a height falls down).This is changed to the energy used to rotate stuff (mechanical energy) in a power plant or power generator, which is then converted into electrical energy. Water is stored behind a dam in a reservoir. In the dam is a water intake. This is a narrow opening to a tunnel called a penstock. Penstock

4. How it works (continued) Water pressure (from the weight of the water and gravity) forces the water through the penstock and onto the blades of a turbine. A turbine is a machine consisting of movable blades. The moving water pushes the blades and turns the turbine. The turbine spins because of the force of the water. The turbine is connected to an electrical generator inside the powerhouse. The generator produces electricity that travels over long-distance power lines to homes and businesses. This is how hydroelectricity is produced

5. Types of dams (energy generators) Masonry dams -dams which are made of stone Embankment dams –dams which are often water barriers that block water flow. Cofferdams –dams which block water flow to a normally flooded area. Timber dams –dams which are made using timber (wood). Steel dams –dams which are made of steel. Beaver dams –dams which are naturally built by beavers. Tarbela dam (Embankment)

6. Strengths and weaknesses of dams Masonry dams- Strengths: Strong, durable, Weaknesses: Will eventually become eroded. Embankment dams- Strengths: Heavy, Usually made of hard material, durable. Weaknesses: Made using multiple materials with different types for the impervious zones and the other zones. Coffer dams- Strengths: Foundation for dams which will otherwise fail to be completed in usually flooded areas. Weaknesses: This sort of dam is usually temporary. Timber dams- Strengths: Fast construction speed, low technology required, cheap,Weaknesses: Not durable, Decomposition of wood will occur if untreated, Limited height that can be built Steel dams- Strengths: Strong, Powerful,Weaknesses: Metals will rust eventually, expensive Beaver dams- Strengths: Natural, can turn ponds into wetlands and marshes which will allow more organisms to live there. Weaknesses: Will eventually decompose, will be abandoned by beavers

7. Has it been successful? Hydroelectricity has been a successful source of energy which is renewable and can be easily generated. Hydroelectricity has been successful and has been used very quickly after Edison used DC or Westinghouse used AC. The first success was on 30 September 1882. Hydroelectricity is still generated today with lots of dams across the world providing electrical energy that is supplied to all our homes. The largest dam that is in construction is the Three Gorges Dam in China which can produce up to 22500MW (Mega watts) of electricity.

8. Facts Hydroelectricity supplies 19 per cent of the world’s current electricity needs and over 63 per cent of renewable energy (Figures in 2005) The first hydroelectric power station in history started producing electricity in 1882. It was located in the state of Wisconsin, and used the Fox River for electrical generation. It was later renamed the Appleton Edison Light Company. Hydroelectricity is used throughout the world such as in China, in the USA, in Vietnam, practically every country that has rivers uses hydroelectricity, regardless or political or economical influence. The reason behind this may be because the energy source is free and renewable. Dams generate electricity by using mechanical energy* to turn turbines or generators like most other ways of creating electricity such as wind turbines or coal power generators. *Mechanical energy is the potential and kinetic energy present in mechanical parts

9. Advantages and disadvantages of dams AdvantagesDisadvantages Renewable source of energy Clean power generation Can prevent floods in flooded areas Energy source is free Creates flooding around the area behind the dam. Requires a lot of materials to build. Washes away trees Uncovers tiny creatures that get eaten by fish Reduces water flow down the river and may eventually cause drought down the river. Can only be built in certain areas of rivers such as areas that can support a new lake.

10. Advantages and disadvantages of tidal power generation AdvantagesDisadvantages Renewable source of energy Clean energy Large area of locations to harvest energy Some power plants can actually be buoys floating around in the ocean, they do not take up much space and they can float around freely. Can only be placed in water Requires tidal or wave activity which is not always available. Tsunamis may damage equipment Larger generators may need to be placed in groups

11. Practical application in real world Three Gorges Dam (China, Yangtze River) Hoover Dam (USA) (Refer to picture on left) Tidal wave energy generator. (see below) Sadd Al-Kafara (Wadi Al-Garawi, Ancient Egypt) The first hydroelectric power plant (Appleton Edison Light Company) (USA, Fox river)

12. Sources http://peswiki.com/index.php/PowerPedia:Ocean_Wave_Energy http://en.wikipedia.org/wiki/Tidal_power http://www.promotega.org/AAU06004/Hydroelectricity.htm http://en.wikipedia.org/wiki/Dam http://hubpages.com/hub/facts-about-hydroelectric-energy http://www.americaslibrary.gov/cgi-bin/page.cgi/jb/gilded/hydro_1

13. Reflection I chose to do an article about hydroelectricity, as I came across it and found it particularly interesting when I was wondering how are people coping with Global Warming, regarding the smoke produced from burning fuel for electricity, last time when I was primary 6. From doing this set of slides, looking it through again and looking up on the internet, as I did forget some stuff about hydroelectrity, I learnt about how electricity can be harvested through the sea, and how the whole process functions.