Topic 8: Energy, power Topic 8: Energy, power and climate changeand climate change

8.4 Non-fossil Fuel Production8.4 Non-fossil Fuel Production

Non-Fossil fuel productionNon-Fossil fuel production

•Nuclear PowerNuclear Power•Solar PowerSolar Power•Hydroelectric PowerHydroelectric Power•Wind PowerWind Power•Wave PowerWave Power

Chain reactionsChain reactions

• Chain reactions can only take place if more neutrons are released than were used during the nuclear reaction.

• Isotopes that produce an excess of neutrons in their fission support a chain reaction.

• This type of isotope is said to be fissionable, • Only two main fissionable isotopes are used during

nuclear reactions — uranium-235 and plutonium-239. • The minimum amount of fissionable material needed to

ensure that a chain reaction occurs is called the critical mass.

Controlled fission

To maintain a sustained controlled nuclear reaction, there To maintain a sustained controlled nuclear reaction, there must be at least one neutron from each fission being must be at least one neutron from each fission being absorbed by another fissionable nucleus. absorbed by another fissionable nucleus.

The reaction can be controlled by using control rods of The reaction can be controlled by using control rods of material which absorbs neutrons. material which absorbs neutrons.

Control rods are commonly made of a strongly neutron-Control rods are commonly made of a strongly neutron-absorbent material such as boron or cadmium.absorbent material such as boron or cadmium.

Uncontrolled fissionUncontrolled fission

A A fissionfission reaction whereby the reaction is allowed to reaction whereby the reaction is allowed to proceed without any moderation or control rods is called proceed without any moderation or control rods is called an an uncontrolled fissionuncontrolled fission reaction . reaction .

If there are too many neutrons, the chain reaction would If there are too many neutrons, the chain reaction would proceed at tremendous pace and result in an explosion.proceed at tremendous pace and result in an explosion.

An example would be in an atomic bomb where the An example would be in an atomic bomb where the reactions are uncontrolled.reactions are uncontrolled.

In a nuclear reactor, if the fission process is not well In a nuclear reactor, if the fission process is not well controlled, the large amounts of energy would cause the controlled, the large amounts of energy would cause the fuel to melt and set fire to the reactor in what is called a fuel to melt and set fire to the reactor in what is called a meltdown. meltdown.

Fuel enrichmentFuel enrichment

• Uranium found in nature consists largely of two Uranium found in nature consists largely of two isotopes, U-235 and U-238. The production of energy in isotopes, U-235 and U-238. The production of energy in nuclear reactors is from the 'fission' or splitting of the U-nuclear reactors is from the 'fission' or splitting of the U-235 atoms, a process which releases energy in the 235 atoms, a process which releases energy in the form of heat. U-235 is the main fissile isotope of form of heat. U-235 is the main fissile isotope of uranium.uranium.

• Natural uranium contains 0.7% of the U-235 isotope. Natural uranium contains 0.7% of the U-235 isotope. The remaining 99.3% is mostly the U-238 isotope which The remaining 99.3% is mostly the U-238 isotope which does not contribute directly to the fission process does not contribute directly to the fission process (though it does so indirectly by the formation of fissile (though it does so indirectly by the formation of fissile isotopes of plutonium).isotopes of plutonium).

Some reactors, for example the Some reactors, for example the Canadian-designed Candu and the Canadian-designed Candu and the British Magnox reactors, use natural British Magnox reactors, use natural uranium as their fuel. uranium as their fuel.

Most present day reactors (Light Water Most present day reactors (Light Water Reactors or LWRs) use enriched Reactors or LWRs) use enriched uranium where the proportion of the U-uranium where the proportion of the U-235 isotope has been increased from 235 isotope has been increased from 0.7% to about 3% or up to 5%. 0.7% to about 3% or up to 5%.

For comparison, uranium used for For comparison, uranium used for nuclear weapons would have to be nuclear weapons would have to be enriched in plants specially designed enriched in plants specially designed to produce at least 90% U-235.to produce at least 90% U-235.

Energy transformations in a nuclear Energy transformations in a nuclear power stationpower station

Sankey diagrams for energy Sankey diagrams for energy efficiency in a nuclear power plantefficiency in a nuclear power plant

The nuclear fuel cycleThe nuclear fuel cycle

Main stages in the nuclear fuel Main stages in the nuclear fuel cyclecycle

Uranium recoveryUranium recovery to extract (or  to extract (or minemine) uranium ore, ) uranium ore, and concentrate (or and concentrate (or millmill) the ore to produce ") the ore to produce "yellowcakeyellowcake" "

ConversionConversion of yellowcake into uranium hexafluoride (UF of yellowcake into uranium hexafluoride (UF66) )

EnrichmentEnrichment to increase the concentration of uranium-235 (U235) in UF to increase the concentration of uranium-235 (U235) in UF66

Fuel fabricationFuel fabrication to convert enriched UF to convert enriched UF66 into fuel (pellets) for nuclear into fuel (pellets) for nuclear

reactors reactors

Use of the fuel in Use of the fuel in reactorsreactors (nuclear power, research, or naval (nuclear power, research, or naval propulsion) propulsion)

Interim storageInterim storage of spent nuclear fuel of spent nuclear fuel

Reprocessing of Reprocessing of high-level wastehigh-level waste (currently not done in the U.S.) (currently not done in the U.S.) [1] [1]

Final disposition (Final disposition (disposaldisposal) of high-level waste ) of high-level waste

Role of control rodsRole of control rods• The control rods, an The control rods, an

important part of the important part of the reactor, regulate or reactor, regulate or control the speed of the control the speed of the nuclear chain reaction, nuclear chain reaction, by sliding up and down by sliding up and down between the fuel rods or between the fuel rods or fuel assemblies in the fuel assemblies in the reactor core. reactor core. 

• The control rods contain material such as cadmium and boron.  Because of their atomic structure cadmium and boron absorb neutrons, but do not fission or split.

• The temperature in the reactor core is carefully monitored The temperature in the reactor core is carefully monitored and controlled.  and controlled. 

• When the core temperature goes down, the control rods When the core temperature goes down, the control rods are slowly lifted out of the core, and fewer neutrons are are slowly lifted out of the core, and fewer neutrons are absorbed.  absorbed. 

• Therefore, more neutrons are available to cause fission.  Therefore, more neutrons are available to cause fission.  This releases more energy and heat.  This releases more energy and heat. 

• When the temperature in the core rises, the rods are When the temperature in the core rises, the rods are slowly lowered and the energy output decreases because slowly lowered and the energy output decreases because fewer neutrons are available for the chain reaction -- the fewer neutrons are available for the chain reaction -- the control rods absorb neutrons that could otherwise hit control rods absorb neutrons that could otherwise hit uranium atoms and cause them to split.  uranium atoms and cause them to split. 

• To maintain a controlled nuclear chain reaction, the To maintain a controlled nuclear chain reaction, the control rods are manipulated in such a way that each control rods are manipulated in such a way that each fission will result in just one neutron, since the other fission will result in just one neutron, since the other neutrons are absorbed by the control rods. neutrons are absorbed by the control rods.

Role of moderatorRole of moderator

• In addition to the need to In addition to the need to capturecapture neturons, the neutrons neturons, the neutrons often have too much kinetic energy. often have too much kinetic energy.

• These These fast neutronsfast neutrons are slowed through the use of a are slowed through the use of a moderator such as moderator such as heavy water and ordinary water.heavy water and ordinary water.

• Some reactors use graphite as a moderator, but this Some reactors use graphite as a moderator, but this design has several problems. design has several problems.

• Once the fast neutrons have been slowed, they are more Once the fast neutrons have been slowed, they are more likely to produce further nuclear fissions or be absorbed likely to produce further nuclear fissions or be absorbed by the control rod.by the control rod.

• Java applet nuclear reactionJava applet nuclear reaction• http://library.thinkquest.org/17940/texts/java/Reaction.hthttp://library.thinkquest.org/17940/texts/java/Reaction.ht

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A nuclear reactorA nuclear reactor

• Inside the "core" where the nuclear reactions take place Inside the "core" where the nuclear reactions take place are the fuel rods and assemblies, the control rods, the are the fuel rods and assemblies, the control rods, the moderator, and the coolant. moderator, and the coolant.

• Outside the core are the turbines, the heat exchanger, Outside the core are the turbines, the heat exchanger, and part of the cooling system. and part of the cooling system.

• The job of the coolant is to absorb the heat from The job of the coolant is to absorb the heat from the reaction. the reaction.

• The most common coolant used in nuclear The most common coolant used in nuclear power plants today is water. power plants today is water.

• In actuality, in many reactor designs the coolant In actuality, in many reactor designs the coolant and the moderator are one and the same.and the moderator are one and the same.

• The coolant water is heated by the nuclear The coolant water is heated by the nuclear reactions going on inside the core. reactions going on inside the core.

• However, this heated water does not boil However, this heated water does not boil because it is kept at an extremely intense because it is kept at an extremely intense pressure, thus raising its boiling point above the pressure, thus raising its boiling point above the normal 100° Celsius. normal 100° Celsius.

Heat exchangerHeat exchanger

• A A heat exchangerheat exchanger is a device built for efficient is a device built for efficient heat transfer from one medium to another heat transfer from one medium to another

• The heated water rises up and passes through The heated water rises up and passes through another part of the reactor, the heat exchanger. another part of the reactor, the heat exchanger.

• The moderator/coolant water is radioactive, so it The moderator/coolant water is radioactive, so it can not leave the inner reactor containment. can not leave the inner reactor containment.

• Its heat must be transferred to non-radioactive Its heat must be transferred to non-radioactive water, which can then be sent out of the reactor water, which can then be sent out of the reactor shielding.shielding.

• This is done through the heat exchanger, which This is done through the heat exchanger, which works by moving the radioactive water through a works by moving the radioactive water through a series of pipes that are wrapped around other series of pipes that are wrapped around other pipes. pipes.

• The metallic pipes conduct the heat from the The metallic pipes conduct the heat from the moderator to the normal water. moderator to the normal water.

• Then, the normal water (now in steam form and Then, the normal water (now in steam form and intensely hot) moves to the turbine, where intensely hot) moves to the turbine, where electricity is produced. electricity is produced.

• We are not able to convert all the internal energy We are not able to convert all the internal energy of the system into useful work but we can extract of the system into useful work but we can extract some useful work through heat engines.some useful work through heat engines.

• The temperature of the reactor is typically limited The temperature of the reactor is typically limited to 570K. Higher temperature tend to damage the to 570K. Higher temperature tend to damage the fuel rods.fuel rods.

• Typically the temperature of the water returning Typically the temperature of the water returning to the heat exchanger is 310Kto the heat exchanger is 310K

• The efficiency of the nuclear plant is about 46%The efficiency of the nuclear plant is about 46%• With further energy used to drive pumps and With further energy used to drive pumps and

pollution control devices, the efficiency is usually pollution control devices, the efficiency is usually reduced to 34%reduced to 34%

Plutonium-239Plutonium-239

U-238 is not fissile but it is useful because it can be used to U-238 is not fissile but it is useful because it can be used to produced Pu-239, a fissionable isotope. produced Pu-239, a fissionable isotope.

First, U-238 becomes U-239 by neutron capture:First, U-238 becomes U-239 by neutron capture:

Then U-239 goes through beta decay to become Neptunium Then U-239 goes through beta decay to become Neptunium

Then Neptunium beta decays into PlutoniumThen Neptunium beta decays into Plutonium

And Pu-239 is fissionable and large amounts of energy is And Pu-239 is fissionable and large amounts of energy is releasedreleased

Plutonium-239 as a nuclear fuelPlutonium-239 as a nuclear fuel

• U-238 is 140 times more abundant than U-235.U-238 is 140 times more abundant than U-235.• The neutrons given off in a U-235 reaction can be used The neutrons given off in a U-235 reaction can be used

to “breed” more fuel if the non-fissionable U-238 is to “breed” more fuel if the non-fissionable U-238 is placed in a “blanket” around the control rods containing placed in a “blanket” around the control rods containing U-235.U-235.

• On average, 2.4 neutrons are produced in a U-235 On average, 2.4 neutrons are produced in a U-235 reaction with 1 neutron required for the next fission and reaction with 1 neutron required for the next fission and 1.4 left for neutron capture by U-238.1.4 left for neutron capture by U-238.

• Suppose there were 100 fissions of U-235 and 240 Suppose there were 100 fissions of U-235 and 240 neutrons are produced.neutrons are produced.

• 100 neutrons will be needed to start the next fission of U-100 neutrons will be needed to start the next fission of U-235 and 140 neutrons will be available for neutron 235 and 140 neutrons will be available for neutron capture.capture.

• Suppose that some neutrons are lost and there are 110 Suppose that some neutrons are lost and there are 110 neutrons available for capture by non-fissionable U-238.neutrons available for capture by non-fissionable U-238.

• This means that there will be 110 fissions of Pu-239. This means that there will be 110 fissions of Pu-239. • Therefore 100 U-235 will produce 110 fissions of Pu-Therefore 100 U-235 will produce 110 fissions of Pu-

239, which is a 10% increase in fuel.239, which is a 10% increase in fuel.

Safety and risks of nuclear powerSafety and risks of nuclear power

• Problems associated with mining of Problems associated with mining of UraniumUranium

• Problems with disposalProblems with disposal• Risk of thermal meltdownRisk of thermal meltdown• Risk of nuclear programs as means of Risk of nuclear programs as means of

nuclear weapon productionnuclear weapon production

Biggest risk for mining of uranium is the Biggest risk for mining of uranium is the exposure of miners to radon-222 gas and exposure of miners to radon-222 gas and other highly radioactive products, as well other highly radioactive products, as well as water containing radioactive and toxic as water containing radioactive and toxic materialsmaterials

In 1950s, a significant number of american In 1950s, a significant number of american miners developed small cell lung cancer miners developed small cell lung cancer due to radon which was the cancer due to radon which was the cancer causing agent.causing agent.

The are concerns over the disposal of waste :The are concerns over the disposal of waste :

- Low-level (radioactive cooling water, lab equipment - Low-level (radioactive cooling water, lab equipment and protective clothing)and protective clothing)

- Intermediate level (coolant)- Intermediate level (coolant)

- High level (fuel rods)- High level (fuel rods)

The products of fission called “ash” include isotopes The products of fission called “ash” include isotopes of strongtium, caesium and krypton which are of strongtium, caesium and krypton which are highly radioactive with half lives of 30 years or less.highly radioactive with half lives of 30 years or less.

The biggest concern is Pu-239 which has a half-The biggest concern is Pu-239 which has a half-life of approx 24,000 years.life of approx 24,000 years.

It is also used in nuclear warheadsIt is also used in nuclear warheads

Presently the disposal methods include deep Presently the disposal methods include deep storage underground.storage underground.

If these methods fail, there would be catastrophic If these methods fail, there would be catastrophic consequencesconsequences

Radioactive waste would find its way into the food Radioactive waste would find its way into the food chain and underground water would become chain and underground water would become contaminated.contaminated.

Provided that reactors are built to standard and Provided that reactors are built to standard and maintained properly, no obvious pollutants maintained properly, no obvious pollutants escape into the atmosphere that would escape into the atmosphere that would contribute to the “greenhouse” effect.contribute to the “greenhouse” effect.

However, even with expensive cooling towers and However, even with expensive cooling towers and cooling ponds, thermal pollution from the heat cooling ponds, thermal pollution from the heat produced by the exchanger process could produced by the exchanger process could contribute to global warming.contribute to global warming.

The disadvantage of possible nuclear power plant The disadvantage of possible nuclear power plant containment failure is always present. containment failure is always present.

Nuclear terrorism is a threat.Nuclear terrorism is a threat.

Nuclear power using nuclear fusion Nuclear power using nuclear fusion

The most probable way is to fuse deuterium The most probable way is to fuse deuterium and tritium.and tritium.

Deuterium atoms can be extracted from Deuterium atoms can be extracted from seawater and tritium can be bred from seawater and tritium can be bred from lithium. lithium.

Nuclear power using nuclear Nuclear power using nuclear fusion?fusion?

The basic problems in attaining useful nuclear The basic problems in attaining useful nuclear fusion conditions are fusion conditions are

(1)(1) to heat the gas to these very high temperatures to heat the gas to these very high temperatures and and

(2)(2) to confine a sufficient quantity of the reacting to confine a sufficient quantity of the reacting nuclei for a long enough time to permit the nuclei for a long enough time to permit the release of more energy than is needed to heat release of more energy than is needed to heat and confine the gas. and confine the gas.

(3)(3) the capture of this energy and its conversion to the capture of this energy and its conversion to electricity. electricity.

Nuclear power using nuclear Nuclear power using nuclear fusion?fusion?

Nuclear fusion was first achieved on earth in the early 1930s Nuclear fusion was first achieved on earth in the early 1930s by bombarding a target containing deuterium, the mass-2 by bombarding a target containing deuterium, the mass-2 isotope of hydrogen, with high-energy deuterons in a isotope of hydrogen, with high-energy deuterons in a cyclotron (Particle accelerator).cyclotron (Particle accelerator).

To accelerate the deuteron beam a great deal of energy is To accelerate the deuteron beam a great deal of energy is required, most of which appeared as heat in the target.required, most of which appeared as heat in the target.

As a result, no net useful energy was produced. As a result, no net useful energy was produced. In the 1950s the first large-scale but uncontrolled release of In the 1950s the first large-scale but uncontrolled release of

fusion energy was demonstrated in the tests of fusion energy was demonstrated in the tests of thermonuclear weapons by the United States, the USSR, thermonuclear weapons by the United States, the USSR, the United Kingdom, and France.the United Kingdom, and France.

This was such a brief and uncontrolled release that it could This was such a brief and uncontrolled release that it could not be used for the production of electric power not be used for the production of electric power

The problem with fusion is the sheer The problem with fusion is the sheer difficulty of achieving the act. difficulty of achieving the act.

Why the very high temperatures?Why the very high temperatures?Atoms have a very strong repulsive force and it takes high Atoms have a very strong repulsive force and it takes high

temperatures and enormous amounts of energy to bring temperatures and enormous amounts of energy to bring them close enough together to fuse. them close enough together to fuse.

And this must be maintained for long periods to produce And this must be maintained for long periods to produce electricity. electricity.

We have been researching fusion for over four decades and We have been researching fusion for over four decades and spent many millions of dollars, pounds and euros. spent many millions of dollars, pounds and euros.

It is possible that more money and time could produce It is possible that more money and time could produce successful fusion in another decade or so, but it may never successful fusion in another decade or so, but it may never be achievable. be achievable.

It might be wiser to spend that time and money on something It might be wiser to spend that time and money on something which we know will succeed such as renewables. which we know will succeed such as renewables.

At temperatures of 100,000° C, all the hydrogen atoms are At temperatures of 100,000° C, all the hydrogen atoms are fully ionized. fully ionized.

The gas consists of an electrically neutral assemblage of The gas consists of an electrically neutral assemblage of positively charged nuclei and negatively charged free positively charged nuclei and negatively charged free electrons. electrons.

This state of matter is called a plasma.This state of matter is called a plasma.A plasma hot enough for fusion cannot be contained by A plasma hot enough for fusion cannot be contained by

ordinary materials. ordinary materials. The plasma would cool very rapidly, and the vessel walls The plasma would cool very rapidly, and the vessel walls

would be destroyed by the extreme heat. would be destroyed by the extreme heat. However, since the plasma consists of charged nuclei and However, since the plasma consists of charged nuclei and

electrons, which move in tight spirals around the lines of electrons, which move in tight spirals around the lines of force of strong magnetic fields, force of strong magnetic fields,

the plasma can be contained in a properly shaped magnetic the plasma can be contained in a properly shaped magnetic field region without reacting with material walls. field region without reacting with material walls.

Why containment?Why containment?

Why is high temp maintained?Why is high temp maintained?

Because fusion is not a chain reaction, Because fusion is not a chain reaction, these temperature and density conditions these temperature and density conditions have to be maintained for future fusion to have to be maintained for future fusion to occur.occur.

If fusion energy does become practical, it offers If fusion energy does become practical, it offers the following advantages: the following advantages:

(1)(1)a limitless source of fuel, deuterium from the a limitless source of fuel, deuterium from the ocean; ocean;

(2)(2)no possibility of a reactor accident, as the no possibility of a reactor accident, as the amount of fuel in the system is very small; and amount of fuel in the system is very small; and

(3)(3)waste products much less radioactive and waste products much less radioactive and simpler to handle than those from fission simpler to handle than those from fission systems. systems.

Photovoltaic cellsPhotovoltaic cells

• Photovoltaic devices make use of the Photovoltaic devices make use of the photoelectric effect. photoelectric effect.

• Solar photovoltaic modules use solar cells to Solar photovoltaic modules use solar cells to convert light from the sun into electricity. convert light from the sun into electricity.

Solar heating panelsSolar heating panels

Solar thermal panels contain liquid that circulates Solar thermal panels contain liquid that circulates through special panels and is heated by through special panels and is heated by sunlight, this then passes through a coil in the sunlight, this then passes through a coil in the water tank which in turn heats the water stored water tank which in turn heats the water stored in the tank in the tank

What are the factors that would What are the factors that would affect the amount of solar affect the amount of solar

radiation that a place gets?radiation that a place gets?

The main factors are:The main factors are:

• Geographic location Geographic location • Time of day (altitude of the sun from the Time of day (altitude of the sun from the

sky)sky)• Season Season • Local landscape Local landscape • Local weather Local weather • The distance of earth from the sunThe distance of earth from the sun

Because the Earth is round, the sun strikes the Because the Earth is round, the sun strikes the surface at different angles ranging from 0º (just surface at different angles ranging from 0º (just above the horizon) to 90º (directly overhead). above the horizon) to 90º (directly overhead).

When the sun's rays are vertical, the Earth's When the sun's rays are vertical, the Earth's surface gets all the energy possible. surface gets all the energy possible.

The more slanted the sun's rays are, the longer The more slanted the sun's rays are, the longer they travel through the atmosphere, becoming they travel through the atmosphere, becoming more scattered and diffuse. more scattered and diffuse.

Because the Earth is round, the frigid polar regions Because the Earth is round, the frigid polar regions never get a high sun, and because of the tilted never get a high sun, and because of the tilted axis of rotation, these areas receive no sun at all axis of rotation, these areas receive no sun at all during part of the year during part of the year

The Earth revolves around the sun in an elliptical The Earth revolves around the sun in an elliptical orbit and is closer to the sun during part of the orbit and is closer to the sun during part of the year. year.

When the sun is nearer the Earth, the Earth's When the sun is nearer the Earth, the Earth's surface receives a little more solar energy. surface receives a little more solar energy.

The Earth is nearer the sun when it's summer in The Earth is nearer the sun when it's summer in the southern hemisphere and winter in the the southern hemisphere and winter in the northern hemisphere. northern hemisphere.

However the presence of vast oceans moderates However the presence of vast oceans moderates the hotter summers and colder winters one the hotter summers and colder winters one would expect to see in the southern hemisphere would expect to see in the southern hemisphere as a result of this difference. as a result of this difference.

The 23.5º tilt in the Earth's axis of rotation is a The 23.5º tilt in the Earth's axis of rotation is a more significant factor in determining the more significant factor in determining the amount of sunlight striking the Earth at a amount of sunlight striking the Earth at a particular location. particular location.

Tilting results in longer days in the northern Tilting results in longer days in the northern hemisphere from the spring (vernal) equinox to hemisphere from the spring (vernal) equinox to the fall (autumnal) equinox and longer days in the fall (autumnal) equinox and longer days in the southern hemisphere during the other six the southern hemisphere during the other six months. months.

Days and nights are both exactly 12 hours long on Days and nights are both exactly 12 hours long on the equinoxes, which occur each year on or the equinoxes, which occur each year on or around March 23 and September 22. around March 23 and September 22.

Countries like the United States, which lie in Countries like the United States, which lie in the middle latitudes, receive more solar the middle latitudes, receive more solar energy in the summer not only because energy in the summer not only because days are longer, days are longer,

but also because the sun is nearly overhead. but also because the sun is nearly overhead.

The sun's rays are far more slanted during The sun's rays are far more slanted during the shorter days of the winter months. the shorter days of the winter months. Cities like Denver, Colorado, (near 40º Cities like Denver, Colorado, (near 40º latitude) receive nearly three times more latitude) receive nearly three times more solar energy in June than they do in solar energy in June than they do in December December

The rotation of the Earth is responsible for The rotation of the Earth is responsible for hourly variations in sunlight. hourly variations in sunlight.

In the early morning and late afternoon, the In the early morning and late afternoon, the sun is low in the sky. Its rays travel further sun is low in the sky. Its rays travel further through the atmosphere than at noon through the atmosphere than at noon when the sun is at its highest point. when the sun is at its highest point.

On a clear day, the greatest amount of solar On a clear day, the greatest amount of solar energy reaches a solar collector around energy reaches a solar collector around solar noon solar noon

3 main schemes3 main schemes

• Water storage in lakesWater storage in lakes• Tidal water storageTidal water storage• Pump storagePump storage

Water storage in lakesWater storage in lakes

Water storage in lakesWater storage in lakes

The Three Gorges Dam on the Yangtze River will be the The Three Gorges Dam on the Yangtze River will be the largest hydroelectric dam in the world when it is largest hydroelectric dam in the world when it is complete in 2009.complete in 2009.

It will generate 18200MWIt will generate 18200MW

The dam is more than 2 km wide and has a height of 185m.The dam is more than 2 km wide and has a height of 185m.

Its reservoir will stretch over 600km upstream and force the Its reservoir will stretch over 600km upstream and force the displacement of more than 1.3million people.displacement of more than 1.3million people.

Tidal water storageTidal water storage

Have been built in Russia and France and in Have been built in Russia and France and in developmental stage in other countriesdevelopmental stage in other countries

Source of energy is the kinetic energy of the earth’s Source of energy is the kinetic energy of the earth’s rotation.rotation.

Coastal estuaries that have a large vertical range in tides Coastal estuaries that have a large vertical range in tides are potential sites for tidal power stationsare potential sites for tidal power stations

The station in France has a tidal range of 8.4m and The station in France has a tidal range of 8.4m and generates 10MW of electrical energy for each of the 24 generates 10MW of electrical energy for each of the 24 turbines.turbines.

Tidal water storageTidal water storageA dam is built to catch the high tide.A dam is built to catch the high tide.

A sluice gate is opened to let the high tide water inA sluice gate is opened to let the high tide water in

The water is released at low tide, and the gravitational The water is released at low tide, and the gravitational potential energy is used to drive turbines which produce potential energy is used to drive turbines which produce electrical energyelectrical energy

Pumped storage Pumped storage

Used in off-peak electricity demand periodUsed in off-peak electricity demand periodWater is pumped from low reservoir to high Water is pumped from low reservoir to high

reservoirreservoir

Generating Mode Pumping Mode

Energy transformationsEnergy transformationsWater trapped in reservoirs have gravitational potential energyWater trapped in reservoirs have gravitational potential energy

Water falls through a series of pipes where its potential energy Water falls through a series of pipes where its potential energy gets converted to rotational kinetic energy that drives a gets converted to rotational kinetic energy that drives a series of turbinesseries of turbines

The rotating turbines drive generators that convert the kinetic The rotating turbines drive generators that convert the kinetic energy into electrical energy by electromagnetic induction.energy into electrical energy by electromagnetic induction.

Installed wind power Installed wind power capacity Rankingcapacity Ranking

1)1) GermanyGermany

2)2) USUS

3)3) SpainSpain

4)4) IndiaIndia

5)5) ChinaChina

6)6) DenmarkDenmark

Check out:Check out:

http://www.world-wind-energy.infohttp://www.world-wind-energy.info//

Basic featuresBasic features

1)1) FoundationFoundation

2)2) TowerTower

3)3) NacelleNacelle

4)4) Rotor bladesRotor blades

5)5) HubHub

6)6) Transformer (not part of Transformer (not part of wind turbine)wind turbine)

1) Foundation and 2) Tower 1) Foundation and 2) Tower Guarantee the stability of a wind turbine a pile or Guarantee the stability of a wind turbine a pile or

flat foundation is used, depending on the flat foundation is used, depending on the consistency of the underlying ground. consistency of the underlying ground.

The The towertower carry the weight of the nacelle and the carry the weight of the nacelle and the rotor blades, AND must also absorb the huge rotor blades, AND must also absorb the huge static loads caused by the varying power of the static loads caused by the varying power of the wind. wind.

Generally, a tubular construction of concrete or Generally, a tubular construction of concrete or steel is used. An alternative to this is the lattice steel is used. An alternative to this is the lattice tower form.tower form.

3) Nacelle and 5) Hub3) Nacelle and 5) HubThe nacelle holds all the turbine machinery. The nacelle holds all the turbine machinery.

Because it must be able to rotate to follow the wind Because it must be able to rotate to follow the wind direction, it is connected to the tower via bearings. direction, it is connected to the tower via bearings.

The build-up of the nacelle shows how the manufacturer The build-up of the nacelle shows how the manufacturer has decided to position the drive train components (rotor has decided to position the drive train components (rotor shaft with bearings, transmission, generator, coupling shaft with bearings, transmission, generator, coupling and brake) above this machine bearing. and brake) above this machine bearing.

4) Rotor and rotor blades4) Rotor and rotor blades

The The rotorrotor is the component which, with the help of the rotor is the component which, with the help of the rotor blades, converts the energy in the wind into rotary blades, converts the energy in the wind into rotary mechanical movement.mechanical movement.

Currently, the three-blade, horizontal axis rotor dominates. Currently, the three-blade, horizontal axis rotor dominates. The The rotor bladesrotor blades are mainly made of glass-fibre or are mainly made of glass-fibre or carbon-fibre reinforced plastics (GRP, CFRP). carbon-fibre reinforced plastics (GRP, CFRP).

The blade profile is similar to that of an aeroplane wing. The blade profile is similar to that of an aeroplane wing. They use the same principle of lift: on the lower side of They use the same principle of lift: on the lower side of the wing the passing air generates higher pressure, the wing the passing air generates higher pressure, while the upper side generates a pull. while the upper side generates a pull.

These forces cause the rotor to move to rotate.These forces cause the rotor to move to rotate.

FYIFYI

Significant areas of the world have mean annual Significant areas of the world have mean annual windspeeds of above 4-5 m/s (metres per second) which windspeeds of above 4-5 m/s (metres per second) which makes small-scale wind powered electricity generation makes small-scale wind powered electricity generation an attractive option. an attractive option.

It is important to obtain accurate windspeed data for the It is important to obtain accurate windspeed data for the site in mind before any decision can be made as to its site in mind before any decision can be made as to its suitability suitability

Power calculationPower calculation

The power in the wind is proportional to:The power in the wind is proportional to:• the area of windmill being swept by the the area of windmill being swept by the

wind wind • the cube of the wind speed the cube of the wind speed • the air density - which varies with altitude the air density - which varies with altitude

FormulaFormula

P = 0.5P = 0.5ρρAv³Av³

WhereWhere

P: is power in watts (W) P: is power in watts (W)

ρ: is the air density in kilograms per cubic metre (kg/m3), ρ: is the air density in kilograms per cubic metre (kg/m3), (about 1.225 kg/m3 at sea level, less higher up) (about 1.225 kg/m3 at sea level, less higher up)

A: is the swept rotor area in square metres (m2) A: is the swept rotor area in square metres (m2)

V: is the windspeed in metres per second (m/s). V: is the windspeed in metres per second (m/s).

The actual power that we can extract from the wind is The actual power that we can extract from the wind is significantly less than what the previous formula significantly less than what the previous formula suggests. The actual power will depend on several suggests. The actual power will depend on several factors, such as factors, such as – the type of machine and rotor used, the type of machine and rotor used, – the sophistication of blade design, the sophistication of blade design, – friction losses, and friction losses, and – the losses in the pump or other equipment the losses in the pump or other equipment

connected to the wind machine. connected to the wind machine.

There are also physical limits to the amount of There are also physical limits to the amount of power that can be extracted realistically from the power that can be extracted realistically from the wind. wind.

It can been shown theoretically that any windmill It can been shown theoretically that any windmill can only possibly extract a maximum of 59.3% can only possibly extract a maximum of 59.3% of the power from the wind (this is known as the of the power from the wind (this is known as the Betz limit). Betz limit).

In reality, this figure is usually around 45% In reality, this figure is usually around 45% (maximum) for a large electricity producing (maximum) for a large electricity producing turbine and around 30% to 40% for a windpump.turbine and around 30% to 40% for a windpump.

Modifying the formula for ‘Power in the wind’ we can say Modifying the formula for ‘Power in the wind’ we can say that the power which is produced by the wind machine that the power which is produced by the wind machine can be given by:can be given by:

Pm = 0.5 CPm = 0.5 Cpp ρ AV³ ρ AV³

WhereWherePm: is power (in watts) available from the machine Pm: is power (in watts) available from the machine CCpp: is the coefficient of performance of the wind machine : is the coefficient of performance of the wind machine

(power efficiency) (power efficiency) rho: is the air density in kilograms per cubic metre (kg/mrho: is the air density in kilograms per cubic metre (kg/m33), ),

(about 1.225 kg/m3 at sea level, less higher up) (about 1.225 kg/m3 at sea level, less higher up) A: is the swept rotor area in square metres (mA: is the swept rotor area in square metres (m22) ) V: is the windspeed in metres per second (m/s). V: is the windspeed in metres per second (m/s).

Wave PowerWave Power

DescribeDescribe the principle of operation of an oscillating water the principle of operation of an oscillating water column (OWC) ocean-wave energy convertercolumn (OWC) ocean-wave energy converter

DetermineDetermine the power per unit length of a wavefront, the power per unit length of a wavefront, assuming a rectangular profile for the wave.assuming a rectangular profile for the wave.

SolveSolve problems involving wave power. problems involving wave power.

Simple animation of OWC:Simple animation of OWC:

http://www.daedalus.gr/DAEI/PRODUCTS/RET/General/Ohttp://www.daedalus.gr/DAEI/PRODUCTS/RET/General/OWC/OWCsimulation2.htmWC/OWCsimulation2.htm

Offshore OWCOffshore OWC Onshore OWCOnshore OWC

As the wave enters a capture chamber, the air As the wave enters a capture chamber, the air inside the chamber is compressed inside the chamber is compressed

and the high velocity air provides the kinetic and the high velocity air provides the kinetic energy needed to drive a turbine connected to a energy needed to drive a turbine connected to a generator. generator.

As the captured water level drops, there is a rapid As the captured water level drops, there is a rapid decompression of the air in the chamber which decompression of the air in the chamber which

again turns the turbine that has been specially again turns the turbine that has been specially designed with a special valve system which designed with a special valve system which turns in the same direction regardless of the turns in the same direction regardless of the direction of the air flowing across the turbine direction of the air flowing across the turbine blades. blades.

http://http://www.darvill.clara.net/altenerg/wave.htmwww.darvill.clara.net/altenerg/wave.htm

http://www.alternative-energy-news.info/technology/hydro/http://www.alternative-energy-news.info/technology/hydro/wave-power/wave-power/

EnergyEnergyPotential energy of the wave over one periodPotential energy of the wave over one period

EEpp = 0.25 w = 0.25 wρρgA²gA²λλ

Kinetic energy of the wave over one periodKinetic energy of the wave over one period

EEkk = = 0.25 0.25 ρρwgA²wgA²λλ

Total energy over one periodTotal energy over one period

EETT = 0.5 w = 0.5 wρρgA²gA²λλ

PowerPowerPower generated (work/time)Power generated (work/time)

P = P = 0.5 w0.5 wρρgA²gA²λλ/T/T

Power per wavelength = 0.5 wPower per wavelength = 0.5 wρρgA²fgA²f

Power per meter = 0.5 wPower per meter = 0.5 wρρgA²v gA²v

where v is the speed of the wavewhere v is the speed of the wave

The density of seawater at the surface of the ocean The density of seawater at the surface of the ocean varies from 1020 to 1029kgmvaries from 1020 to 1029kgm-3-3..

ρρ= = Water densityWater density

W = wave width, assumed to be the width of the chamberW = wave width, assumed to be the width of the chamber

A = wave amplitudeA = wave amplitude

T = wave periodT = wave period

ΛΛ= wavelength= wavelength