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Solar Energy IV Hydroelectricity and OTEC

n n Hydro power has a very long history with watermills appearing as early as 100 BC. By 1200 it was used to operate hammers in ironworks

n n By 1500 it was the primary source of industrial power. Rivers and streams were a critical source of power and transportation in the settling of America.

First Hydroelectric Generator n n Located at Cragside, a country house in Northumberland, England. In 1870, water from one of the estate's lakes was used to drive a Siemens dynamo in what was probably the world's first hydroelectric power station.

Today Hydropower is used mainly for generating electricity

Water cycle as a great big heat engine

Generators inside Hoover Dam

Convert Potential Energy of Water Into Kinetic Energy to Run a Generator n n n mgh=mv 2/2 h is called the “head” of the dam Modern hydroelectric plants convert ~90% of PE into electricity

High Head Dams n n n h is up to 1000 ft. A lot of energy per liter of water that flows through. Can get by with smaller flows.

Low Head Dams n n n As low as 10 ft. Not much energy per liter of water. Need a higher flow rate to get as much electricity

Sample Calculation n n Useful information: 1 liter of H 2 O has a mass of 1 kg. Height of Hoover Dam = 221 m Power rating of Hoover Dam is 2, 451 MW. Find the amount of water that flows through the dam per second if it is 90% efficient.

n n Electrical power form 1 liter of water per second. P =(0. 9)(1 kg/s)(9. 8 m/s 2)(221 m) =1. 949 k. W

US Hydroelectric Production

Existing hydroelectric plants (yellow) and potential high head/low power energy sites (orange)

Principal Dams in the US

Top Ten Countries for Hydroelectricity Country Annual Hydroelectric Production (TWh) Installed Capacity Factor Percent of all electricity China 652. 05 196. 79 0. 37 22. 25 Canada 369. 5 99. 974 0. 59 61. 12 Brasil 363. 8 69. 080 0. 56 85. 56 United States 250. 6 79. 511 0. 42 5. 74 Russia 167. 0 45. 000 0. 42 17. 64 Norway 140. 4 27. 528 0. 49 98. 25 India 115. 6 33. 600 0. 43 15. 8 Venezuela 86. 8 Japan 69. 2 27. 229 0. 37 7. 21 Sweden 65. 5 16. 209 0. 46 44. 34 67. 17

Top Ten Largest Hydroelectric Plants Dam Country Completed Power (GW) Three Gorges Dam China 2008/11 18. 3/22. 5 Itaipu Brazil/Paraguay 1984/91/03 14. 0 Guri (Simon Bolivar) Venezuela 1986 10. 2 Tucurui Brazil 1984 8. 37 Grand Coulee United States 1942/80 6. 81 Sayano Shushenskaya Russia 1985/89 6. 4 krasnoyarskaya Russia 1972 6. 0 Robert-Bourassa Canada 1981 5. 62 Churchill Falls Canada 1971 5. 43 Longtan Dam China 2009 4. 9/6. 3

Three Gorges Dam (World’s Largest)

Ten largest Dams Under Construction Project Country Capacity (GW) Completion Xiluodu Dam China 12. 6 2015 Siang Upper HE Project India 11. 0 2024 Ta. Sang Dam Burma 7. 1 2022 Xiangjiaba Dam China 6. 4 2015 Nuozhadu Dam China 5. 9 2017 Jinping 2 HP Station China 4. 8 2014 Laxiwa Dam China 4. 2 2010 Xiaowan Dam China 4. 2 2012 Jinping 2 HP Station China 3. 6 2014 Pubugou Dam China 3. 3 2010

Whacky Idea (2007) Red Sea Dam n The idea is to dam the Red Sea at its southern end where the Bab-al-Mandab Strait is only 18 miles (29 km) wide. Natural evaporation would rapidly lower the level of the enclosed Red Sea. Water allowed back into the sea would drive turbines to generate electricity. It is claimed that up to 50 gigawatts would be generated, dwarfing all other power schemes.

Advantages to hydroelectric power: q Fuel is not burned so there is minimal pollution. q Water to run the power plant is provided free by nature. q Hydropower plays a major role in reducing greenhouse gas emissions. q Relatively low operations and maintenance costs. q The technology is reliable and proven over time q It's renewable - rainfall renews the water in the reservoir, so the fuel is almost always there.

n Reservoirs can be used for other purposes such as irrigation, recreation, flood control

Disadvantages n n n Lifetime of 50 to 200 years because of silting. Large environmental changes downstream. Loss of free flowing water. Loss of land flooded by reservoir. Often upstream from large population centers (Huge catastrophe if dam fails. )

n n n n High investment costs Hydrology dependent (precipitation) Inundation of land wildlife habitat Loss or modification of fish habitat Fish entrainment or passage restriction Changes in reservoir and stream water quality Displacement of local populations

Dam Failures n n From 1918 -58 there were 33 dam failures in the US resulting in 1680 deaths. Between 1959 and 65 there were 9 large failures worldwide. It is unusual, but a significant hazard. Terrorists?

Water pouring out of the reservoir of the Teton Dam in Idaho following its catastrophic failure on June 5, 1976. Teton Dam Failure

Ocean Thermo Electric Conversion Use temperature difference between the surface and deep water to drive a heat engine. n Typically very low efficiency, but no cost for fuel. n Typically T 20 K and Th 20 K, thus ec= T/Th 20/300=6. 7% Real efficiency more like 2 -3% n

n n Requires a huge flow of water. A 100 MW plant would require approximately 25, 000 liters per second of both warm and cold water.

n n Use in locations with warm surface waters. T>17 C Predictable power output since T is very stable over the course of a day.

n n Not a whole lot currently being developed. 1930’s : concept plant built near Cuba generated 22 k. W of power, but used more than it generated. 1970’s : small test plant built in Hawaii. No government support since the 1980’s.

Other Ideas n n Large underwater turbines anchored to the sea floor. Ex: Gulf stream has a steady flow that is 1000 time larger than the Mississippi River with a maximum velocity of 4 mph.