Interlude Energy Resources

Interlude Energy Resources

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Energy Transformation Technology into

A system that converts energy from some source a usable form. This is known also as Energy Converter. An example of an energy transformation technology is an electrical generating station. It converts energy such as chemical potential energy stored in coal, oil or natural gas, into electrical energy. Almost all energy transformation technologies operate at efficiencies less than 100%. A lot of the wasted energy becomes thermal energy:

efficiency = Eout / Ein x 100% 2

Typical efficiencies of energy transformation technologies Device

Electric heater

Efficiency (%)

100

Electric generator

98

Hydroelectric power plant

95

Large electric motor

95

Home gas furnace

85

Wind generator

55

Fossil fuel power plant

40

Automobile engine

25

Fluorescent light

20

Incandescent light

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Automobile Efficiency Cars, trucks, boats, airplanes and other vehicles that burn fuel to operate are common energy transformation technologies. To learn about the efficiency of these technologies, let’s focus on the automobile. Suppose that an amount of fuel containing 1000 J of chemical potential energy is used by an automobile’s engine. Chart 1 (next slide) shows what happens to this energy. The efficiency of the car is: efficiency = Eout / Ein x 100% = 100 J /1000 J x 100% = 10 %

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yUsefor every1000Joules AutomobileEnerg efficiency Engine = 750 Joules

Engine Transmission Useful energy Transmission = 150 Joules

Only 100 J or 10% of useful work is done in producing the kinetic energy of the moving car.

Chart 1

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Practice: 3.(a) Calculate the efficiency of the car engine described in Chart 1 up to the point the energy reaches the transmission. (b) Why is the efficiency of the entire car shown to be only 10%, less than the value you determined in (a)? 5.Assume that a fossil fuel power plant has an output of 2500 MW and an efficiency of 38%. (a) Determine the energy output in one day. (b) Calculate the input energy required to produce this output energy. Solution:

2500 MW x J/sec x 8.64 x 104 sec/day = 2.16 x

1014 J (b) Input req’d = 2.16 104 J / 0.38 = 5.7 104 J

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Energy Resources energy resource a raw material obtained from nature that can be used to do work. renewable energy resource an energy resource is considered renewable if it renews itself in the natural human lifespan. non-renewable energy resource all energy resources other than renewable. 7

Non-Renewable Energy Resources Fossil fuels comes from plant decays buried deep and compressed into various new forms. Since it takes millions of years for plant life to become useful fuels, once consumed, they are gone forever.

they

Fossil fuels are extracted raw from the ground. By some form of energy transformation technology, are converted to useful fuel used to generate steam, electricity , and to operate engines, etc.

Major fossil fuels Fuel

State

Compositi on

Energy content per Kilogram (MJ)

Coal

Solid

70% C

28

Lignite

Solid

30% C

12

Gasoline

Liquid

Varies

44

Kerosene

Liquid

Varies

43

Methane

Gas

CH4

49

Ethane

Gas

C 2H 6

44

Propane

Gas

C 3H 8

43

Note:

All values are approximate. 9

How Coal Forms The coal we find today formed from generations of plants that died in ancient tropical swamps and accumulated on the swamp bottoms. The plant material first formed a compact organic material called peat. As layers of sediment gradually accumulated over the peat, the pressure and heat exerted by the thickening layers gradually drove out the moisture and increased the carbon content of the peat, forming coal. 10

…non-renewable energy resource

uranium Uranium undergoes nuclear fission, in which the nucleus (core) of each atom splits, and in doing so, releases a relatively large amount of energy, which heats water. For electrical energy production, uranium thus serves the same function as fossil fuels.

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Nuclear Power Plant

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Renewable Energy Resources solar energy radiant energy from the Sun which can be used to produce small amounts of electrical energy when it strikes photovoltaic cells. These cells are used in satellites and such instruments as calculators. passive solar heating refers to the process of designing and building a structure to take best advantage of the Sun’s energy at all times of the year. The Sun’s rays enter such a building in winter, but not in summer! active solar heating system absorbs the Sun’s energy and converts it into other forms of energy such as electricity. Solar cells placed on slanted south-facing roof can convert light energy into electrical energy. 13

Passive Solar Energy Active solar heating systems involve installing special equipment that uses energy from the sun to heat or cool existing structures. Passive solar energy systems involve designing the structures themselves in ways that use solar energy for heating and cooling. For example, in this home, a “sun space” serves as a collector in winter when the solar shades are open and as a cooler in summer when the solar shades are closed. Thick concrete walls modulate wide swings in temperature by absorbing heat in winter and insulating in summer. Water compartments provide a thermal mass for storing heat during the day and releasing heat at night.

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hydraulic energy comes indirectly from solar energy. Radiant energy evaporates water on Earth, which then rises, condenses into clouds and falls as rain. The rain gathers in rivers and lakes and has gravitational potential energy at the top of a dam or waterfall. This energy can then be changed to useful form, such as electricity. wind energy again caused indirectly by solar energy. Wind generators can change the kinetic energy of the wind into clean, non-polluting electrical energy, or into energy for pumping water. 15

Hydroelectric Power Many countries and states draw on waterpower for energy. Development of dam systems is both expensive and potentially damaging to the environment, so dams are generally carefully planned, financed, and managed by the government. In 1933, for instance, the U.S. Congress created a federal corporation known as the Tennessee Valley Authority (TVA) to develop the natural resources of the Tennessee Valley. The Norris Dam on the Clinch River, shown here, was one of the TVA’s first dams, finished in 1936. 16

Wind Farm These turbines are part of a wind farm located near Lake Benton, Minnesota. This region is one of the most productive wind energy sites in the midwestern United States.

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tidal energy due to gravitational forces of the Moon and the Sun on Earth. To obtain energy from tidal action, a dam must first be built across the mouth of a river that empties into the ocean. The gates of the dam are opened when the tide rolls in. The moving water spins turbines which produce electricity. When the tide stops rising, the gates are closed until low tide nears. Then the gates are opened and the trapped water rushes out past the turbines, once again producing electricity.

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biomass energy chemical potential energy stored in plants and animal wastes. Burning wood and trash are common sources of such energy. Another is the fermentation of sugar molecules in grain by bacteria to produce methane and ethanol (grain alcohol).

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geothermal energy thermal energy or heat taken from beneath the Earth’s surface. It results from radioactive decay (the nuclear fission of elements in rocks). Hot springs and geysers spew forth hot water and steam from within the Earth’s crust. If the rocks are hot and dry, certainly no water will come to the surface. To utilize this heat, two holes are drilled deep into the ground a set distance apart. Water is poured down one hole and it gains energy as it seeps through the hot, porous rocks. Then the water rises up the other hole. The circulating water runs turbines to produce electricity.

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Formation of Geysers Geysers are caused when underground chambers of water are heated to the boiling point by volcanic rock. When heat causes the water to boil, pressure forces a superheated column of steam and water to the surface.Because most geothermal reservoirs are capped by overlying rock, the heated water cannot escape, remaining underground instead. If a geothermal reservoir is sufficiently close to the surface, the heated water can be piped to the surface and used to produce energy. 21