Energy and

Society

Professor Ani Aprahamian

Renewal Energy Resources almost inexhaustible…

Now we will start talking about Solar/Wind/Hydropower

Earth is tilted at 23 degrees above the point on earth where the sun is at its zenith on noon…

Breakdown of the incoming Solar energy

Hydropower, hydraulic power or water power is power that is derived from the force or energy of moving water, which may be harnessed for useful purposes.

Prior to the widespread availability of commercial electric power, hydropower was used for irrigation, and operation of various machines, such as watermills, textile machines, sawmills, dock drances, and domestic lifts.

Hydro-electricityToday the largest use of hydropower is for the creation of hydroelectricity, which allows low cost energy to be used at long distances from the water source. Hydroelectricity is electricity generated by hydropower, i.e., the production of power through use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy. Once a hydroelectric complex is constructed, the project produces no direct waste, and has a considerably different output level of the greenhouse gas carbon dioxide (CO2) than fossil fuel powered energy plants. Worldwide, hydroelectricity supplied an estimated 715,000 MWe in 2005. This was approximately 19% of the world's electricity (up from 16% in 2003), and accounted for over 63% of electricity from renewable sources.

The world's largest is the Three Gorges Dam on the third longest river in the world, the Yangtzi River. Apart from a few countries with an abundance ofhydro power, this energy source is normally applied to peak load demand, because it is readily stopped and started. It also provides a high-capacity,low-cost means of energy storage, known aspumped storage.

drainage area of 1 million km 2 , with an average annual runoff of 451 billion m3

Three Gorges Dam will provide one ninth of China's total power output(The total electric generating capacity of the dam will reach 22,500 MW.)The dam controls flooding, enhances navigation, and provides a vast amount of clean electricity.

Hoover Dam on the Colorado River

Length 1244 ft (379 m)

Height 726.4 ft (221 m)

Base width 660 feet (201m)

Crest width 45 ft (14 m)

Volume3,250,000 cu yd (2,480,000 m3)

Type of spillway 2 x controlled drum-gate

Discharge capacity of spillway

400,000 cu ft/s (11,000 m3/s)

Construction began 1931

Opening date 1936

Construction cost $49 million

Hoover Dam on the Colorado River

Courtesy of BBC: Three Gorges Dam

Yangtze river or Chang Jiang

China's controversial Three Gorges Dam project hits a significant milestone on Saturday, when it is expected to reach its final height of 185m (607 feet). But it will not be fully operational until 2009.

The project was begun in 1993 at an official cost of 200 billion yuan ($25bn), though unofficial estimates Are far higher.

When the dam's reservoir reaches its final height of 175m, the five-chamber shiplock will raise boats by as much as 113m.

The primary aims of the dam are to alleviate floodingon the Yangtze River and generate power. Fourteen turbine generator units are already in operation.

At least 1 million people were relocated to make way for the project.

Those made homeless by the dam are being moved to new townships. Some say they miss their old homes; others are pleased to have modern facilities.

Flood Control

Energy Generation

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Tourism

A water turbine is a rotary engine that takes energy from moving water.

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Example

WE are taking energy stored….potential energy Converting to kinetic energy……………………………

Potential energy can be thought of as energy stored within a physical system. It is called potential energy because it has the potential to be converted into other forms of energy, particularly kinetic energy, and to do work in the process.

The standard (SI) unit of measure for potential energy is the joule, the same as for work or energy in general.

Amount of power you can get out…

Total flow

Height….

Calculate the flow rate of water (l/s or kg/s) required to provide 100 kW Of Electric power if the water falls for a vertical distance of 100m…Assume 75% efficiency.

Potential energy: Gravitational E = mgh…………………Joules

Power= Energy/time …………………………………….Joules/s=Watts

Mgh/s= (1kg/s)(9.8m/s2)(100m)=980 kg.m2/s3 980 Watts from 1kg/s

100 kiloWatts=100,000 Watts

980 Watts*0.75= 735 Watts produced by 1 kg/s

100,000 Watts/735 Watts= 1360.5 kg/s = 1360.5 l/s

Density of water 1000kg/m3

1 joule= 1kg.m2/s2 ; One liter is composed of 1,000 cubic centimeters (cc); 1kg

A river has an annual flow rate of 43,000 km3 per year.Suppose you could harness 10% of that flow into hydro-electricdams that have water dropping through a distance of 300m.

Assume 90% efficiency in converting the water’s energy to electricity…What would be the total output of electrical power?

1000kg/m3 density of water3.15x107 s in one year109 m3 in km3

43,000km 3 x 109 m3/km3 x 1000kg/m3 = 43 x1015 kg of water/yr

43x1015 kg of water/yr x 1 yr/3.15x107 s= 1.365 x 109 kg/s

Potential Energy= mgh = 1.365x109 kg/s (9.8m/s2) (300m)= 4.013 x 1012 Watts

Taking into account the efficiencies (0.9)(0.1) = 0.36 x 1012 Watts

Wind Power……………….on land, off-shore,

Wind Energy system……………Wind turns a rotor made of blades/vanesRotor connected to a shaft….electric generator

Power that can be extracted from the wind is proportional to the cube of the wind’s velocity and the area swept out by the blades

80-Meter Wind Resource Maps

Can’t store the energy……….

Kinetic Energy = ½ mv2

Mass= mass of air that hits the wind-generator blades in a unit of time

Velocity of wind……v

Motion of blades….1/2 mv2

Power that can be extracted from the wind is proportional to the cube ofhe wind’s velocity and the area swept out by the blades…….

Why Cube?

Power output is also related to the area swept out by the blades; Area= diameter 2

Maximum achievable efficiency by wind turbines 59%

Maximum power output= 2.83 x 10-4 d2v3 kWatts ; 2.36x10-6 d2v3

D is in meters; v=m/s ; d is in feet; v= miles/hr

What is the maximum achievable power output of a wind turbineof blade radius 2m in a 25 mph wind?

2.36x10-6 d2v3

Diameter = 2 x radius = 4m convert to feet…..4m x 3.28 ft/m= 13.08 ft

Power = (13.08ft)2 (2.36x10-6) (25 mph)3

= 6.3 kWatts