Hydroelectricity & OTEC

Watermills appeared as early as 100 BC. Watermills appeared as early as 100 BC. By 1200 water was used to operate hammers in ironworks By 1200 water was used to operate hammers in ironworks By 1500 it was the primary source of industrial power By 1500 it was the primary source of industrial power Today hydropower is used primarily to generate electricity Today hydropower is used primarily to generate electricity

First Hydroelectric Generator Located at Cragside, a country house in Northumberland, England. Located at Cragside, a country house in Northumberland, England. country house Northumberland England country house 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. 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.1870Siemens dynamo power station1870Siemens dynamo power station

Water cycle as a great big heat engine

Convert Potential Energy of Water Into Kinetic Energy to Run a Generator Potential Energy  Kinetic Emergy Potential Energy  Kinetic Emergy mgh = ½mv 2 mgh = ½mv 2 h is called the “head” of the dam h is called the “head” of the dam Modern hydroelectric plants convert ~90% of PE into electricity Modern hydroelectric plants convert ~90% of PE into electricity

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

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

Example 1 liter of H 2 O has a mass of 1kg. 1 liter of H 2 O has a mass of 1kg. Head of Hoover Dam = 221 m Head of Hoover Dam = 221 m Power rating of Hoover Dam is 2,451 MW. Power rating of Hoover Dam is 2,451 MW. If the dam is 90% efficient at generating electricity how much water that flows through the dam per second? If the dam is 90% efficient at generating electricity how much water that flows through the dam per second?

Example 1 W = 1 J/s 1 W = 1 J/s 2,451 MW of electricity needs 2723 MW from water 2,451 MW of electricity needs 2723 MW from water x 10 9 J/s = m(9.8m/s 2 )(221m) x 10 9 J/s = m(9.8m/s 2 )(221m) m = x 10 9 J/s/ m2/s 2 m = x 10 9 J/s/ m2/s 2 m = x 10 6 kg/s m = x 10 6 kg/s m = x 10 6 l/s m = x 10 6 l/s

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 CountryAnnual Hydroelectric Production (TWh) Installed Capacity Capacity Factor Percent of all electricity China Canada Brasil United States Russia Norway India Venezuela Japan Sweden

Top Ten Largest Hydroelectric Plants DamCountryCompletedPower (GW) Three Gorges DamChina2008/1118.3/22.5 ItaipuBrazil/Paraguay1984/91/ Guri (Simon Bolivar)Venezuela TucuruiBrazil Grand CouleeUnited States1942/ Sayano ShushenskayaRussia1985/896.4 krasnoyarskayaRussia Robert-BourassaCanada Churchill FallsCanada Longtan DamChina /6.3

Three Gorges Dam (World’s Largest)

Ten largest Dams Under Construction ProjectCountryCapacity (GW)Completion Xiluodu DamChina Siang Upper HE Project India TaSang DamBurma Xiangjiaba DamChina Nuozhadu DamChina Jinping 2 HP Station China Laxiwa DamChina Xiaowan DamChina Jinping 2 HP Station China Pubugou DamChina

Whacky Idea (2007) Red Sea Dam 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. 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.Red Sea Bab-al-Mandab StraitRed Sea Bab-al-Mandab Strait

Hydroelectric Power Advantages Fuel is not burned so there is minimal pollution. Fuel is not burned so there is minimal pollution. Major role in reducing greenhouse gases Major role in reducing greenhouse gases Water provided free. Water provided free. Relatively low operations and maintenance costs. Relatively low operations and maintenance costs. Reliable and proven technology. Reliable and proven technology. Renewable – reservoir water renewed by rainfall. Renewable – reservoir water renewed by rainfall.

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

Hydroelectric Power Disadvantages Lifetime of 50 to 200 years due to silting. Lifetime of 50 to 200 years due to silting. Large environmental changes upstream and downstream. Large environmental changes upstream and downstream. Fish, wildlife, and peopleFish, wildlife, and people Loss of free flowing water. Loss of free flowing water. Loss of land flooded by reservoir. Loss of land flooded by reservoir. Often upstream from population centers. Often upstream from population centers. High investment costs High investment costs Hydrology dependent (precipitation) Hydrology dependent (precipitation)

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

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

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

Ocean Thermal Electric Conversion Uses temperature difference between the surface and deep water to drive a heat engine. Uses temperature difference between the surface and deep water to drive a heat engine. Very low efficiency, but no fuel cost. Very low efficiency, but no fuel cost. Typically T  20K and T h  300K so e c = T/T h  20/300 = 6.7% Typically T  20K and T h  300K so e c = T/T h  20/300 = 6.7% True efficiency more like 2-3% True efficiency more like 2-3%

Ocean Thermal Electric Conversion Requires a large water flow. Requires a large water flow. A 100 MW plant would require approximately 25,000,000 liters per second of both warm and cold water. A 100 MW plant would require approximately 25,000,000 liters per second of both warm and cold water. Should have T > 17C which means locations with warm surface waters. Should have T > 17C which means locations with warm surface waters. Predictable power output since T is very stable over the course of a day. Predictable power output since T is very stable over the course of a day.

Not much current development. Not much current development. 1930’s : concept plant built near Cuba generated 22kW of power, but used more than it generated. 1930’s : concept plant built near Cuba generated 22kW of power, but used more than it generated. 1970’s : small test plant built in Hawaii. 1970’s : small test plant built in Hawaii. No government support since the 1980’s. No government support since the 1980’s.

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