4 - Energy resources and energy transfers (copy)

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59 Terms

1

Chemical energy store

Anything that can release energy by chemical reaction
e.g. food, fuels

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2

Kinetic energy store

Anything moving has energy in kinetic energy store

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3

Gravitational energy store

Anything in a gravitational field

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4

Elastic energy store

Anything stretched, like springs and rubber bands

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5

Thermal energy store

Any object - hotter = more energy in thermal store

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6

Magnetic energy store

Magnets interacting with each other have energy in magnetic store
e.g. two magnets attract/repel each other

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7

Electrostatic energy store

Charged objects interacting with each other have energy in electrostatic store
e.g. two charges attract/repel each other

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8

Nuclear energy store

Atomic nuclei release energy from nuclear store in nuclear reactions

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9

Mechanical energy transfer

Object moving due to force acting on it
e.g. pushing, pulling, stretching

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Electrical energy transfer

Charge moving through p.d.
e.g. charges moving around circuit

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Energy transfer by heating

Energy transferred from hotter object to colder object
e.g. heating pan of water on hob

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Energy transfer by radiation

Energy transferred by EM waves
e.g. energy from Sun reaching Earth as light

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13

Principle of conservation of energy

Energy can be stored, transferred between stores and dissipated - but never created/destroyed

Total energy of closed system has no net change

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Formula: Efficiency

Efficiency = useful energy output / total energy output x 100%

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15

Ball rolling up slope

Energy transferred mechanically from kinetic store of ball to its gravitational potential store

Some energy is transferred mechanically to thermal energy stores of ball and slope (due to friction) and then by heating to thermal energy stores of surroundings - energy is wasted

<p>Energy transferred<strong> mechanically </strong>from <strong>kinetic</strong> store of ball to its <strong>gravitational potential</strong> store</p><p>Some energy is transferred <strong>mechanically </strong>to <strong>thermal </strong>energy stores of ball and <strong>slope </strong>(due to <strong>friction</strong>) and then <strong>by heating</strong> to <strong>thermal </strong>energy stores of <strong>surroundings</strong> - energy is <strong>wasted</strong></p>
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16

Bat hitting ball

Some energy usefully transferred mechanically from kinetic store of bat to kinetic store of ball

Rest of energy is wasted

Some energy in kinetic energy store of bat is transferred mechanically to thermal stores of bat, ball and surroundings

Remaining energy is carried away by sound

<p>Some energy <strong>usefully transferred mechanically </strong>from <strong>kinetic </strong>store of bat to <strong>kinetic </strong>store of ball</p><p>Rest of energy is wasted</p><p>Some energy in kinetic energy store of bat is transferred <strong>mechanically </strong>to <strong>thermal </strong>stores of bat, ball and surroundings</p><p>Remaining energy is carried away by <strong>sound</strong></p>
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Electric kettle boiling water

Energy transferred electrically from mains to thermal store of kettle’s heating element

Then transferred by heating to thermal store of water

Some energy wasted, and transferred by heating from thermal stores of heating element and water to thermal stores of surroundings

<p>Energy transferred <strong>electrically</strong> from mains to <strong>thermal </strong>store of kettle’s <strong>heating element</strong></p><p>Then transferred <strong>by heating</strong> to <strong>thermal </strong>store of water</p><p>Some energy <strong>wasted</strong>, and transferred <strong>by heating</strong> from thermal stores of heating element and water to thermal stores of <strong>surroundings</strong></p>
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18

Battery-powered toy car

Energy usefully transferred electrically from chemical store of battery to kinetic store of car and carried away by light from headlights

Energy wasted by transferring to thermal stores of car and surroundings, and wastefully carried away by sound

<p>Energy usefully transferred <strong>electrically </strong>from <strong>chemical </strong>store of <strong>battery</strong> to <strong>kinetic </strong>store of car and carried away by <strong>light</strong> from headlights</p><p><strong>Energy </strong>wasted by transferring to <strong>thermal </strong>stores of car and surroundings, and wastefully carried away by <strong>sound</strong></p>
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19

Bunsen burner and beaker

Energy usefully transferred by heating from chemical store of gas to thermal store of beaker and water

Energy wastefully transferred by heating to thermal stores of stand and surroundings
Some energy carried away by light

<p>Energy usefully transferred<strong> by heating </strong>from <strong>chemical </strong>store of gas to <strong>thermal</strong> store of beaker and water</p><p>Energy <strong>wastefully </strong>transferred by heating to <strong>thermal </strong>stores of stand and surroundings<br>Some energy carried away by <strong>light</strong></p>
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20

Sankey diagrams

Thicker arrow = more energy it represents - thick arrow going in, then several smaller arrows going off it to show different energy transformations occurring

<p><strong>Thicker arrow </strong>= <strong>more energy</strong> it represents - <strong>thick arrow going in</strong>, then several <strong>smaller arrows going off </strong>it to show different energy transformations occurring<strong> </strong></p>
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21

Example of Sankey diagram

knowt flashcard image
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22

Conduction

In solid, particles are held tightly together
When one particle vibrates, it collides with nearby particles and vibrations quickly pass from particle to particle

Process continues throughout solid and gradually some energy is passed all the way through solid, causing rise in temp at other side of solid

<p>In solid, particles are held <strong>tightly</strong> together<br>When one particle <strong>vibrates</strong>, it <strong>collides</strong> with nearby particles and vibrations quickly pass from particle to particle</p><p>Process continues <strong>throughout solid</strong> and gradually some energy is passed all the way through solid, causing <strong>rise in temp</strong> at other side of solid</p>
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23

Convection

When more energetic particles move from hotter region to cooler region, transferring energy as they do so

Only in liquids/gases

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24

Radiation

All objects emit IR radiation

Hotter object = more IR radiation emitted

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25

Immersion heater

  • Energy is transferred from heater coils to thermal energy store of water by conduction

  • Particles near coils get more energy, so they move faster
    Meaning there’s more distance between them i.e. water expands and becomes less dense

  • Reduction in density means that hotter water rises above denser, cooler water

  • As hot water rises, it cools and becomes denser

  • Cold water is heated by coils and rises - process repeats

  • Results in convection currents going up, round and down, circulating energy through water

<ul><li><p><strong>Energy </strong>is <strong>transferred</strong> from heater coils to thermal energy store of water by <strong>conduction</strong></p></li><li><p><strong>Particles</strong> near coils get <strong>more energy</strong>, so they <strong>move faster</strong><br>Meaning there’s more distance between them i.e. water <strong>expands</strong> and becomes <strong>less dense</strong></p></li><li><p>Reduction in density means that <strong>hotter water rises above denser</strong>, <strong>cooler water</strong></p></li><li><p>As <strong>hot water</strong> rises, it <strong>cools </strong>and becomes <strong>denser</strong></p></li><li><p>Cold water is <strong>heated by coils</strong> and rises - process repeats</p></li><li><p>Results in <strong>convection currents</strong> going up, round and down, <strong>circulating </strong>energy through water</p></li></ul>
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26

Emission and absorption of radiation

Hotter object = more IR radiation emitted

Black objects are best at emitting + absorbing thermal radiation

Shiny objects are worst at emitting + absorbing thermal radiation

<p><strong>Hotter object </strong>= <strong>more IR radiation</strong> emitted</p><p><strong>Black </strong>objects are <strong>best </strong>at emitting + absorbing thermal radiation</p><p><strong>Shiny </strong>objects are <strong>worst </strong>at emitting + absorbing thermal radiation</p>
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27

Investigating thermal conduction

  • Attach beads at regular intervals (e.g. every 5cm) to one half of a long (at least 30cm) metal bar using wax

  • Hold metal bar in clamp stand and heat side of bar (using Bunsen burner) with no beads attached from end

  • As time passes, energy is transferred along bar by conduction and temp increases along rod

  • Wax holding beads will gradually melt and beads will fall as temp increases, starting with bead closest to point of heating

<ul><li><p>Attach <strong>beads</strong> at regular intervals (e.g. <strong>every 5cm</strong>) to one half of a <strong>long </strong>(at least 30cm) <strong>metal bar </strong>using <strong>wax</strong></p></li><li><p>Hold metal bar in clamp stand and <strong>heat </strong>side of bar (using Bunsen burner) with <strong>no beads</strong> attached from <strong>end</strong></p></li><li><p>As time passes, <strong>energy</strong> is transferred along bar by <strong>conduction</strong> and <strong>temp increases</strong> along rod</p></li><li><p>Wax holding beads will gradually <strong>melt</strong> and beads will <strong>fall</strong> as temp increases, starting with bead <strong>closest</strong> to point of heating</p></li></ul>
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28

Investigating thermal convection

  • Place some purple potassium permanganate crystals in one side of beaker of cold water

  • Using Bunsen burner, gently heat side of beaker with crystals at bottom

  • As temp of water around potassium permanganate crystals increases, they begin to dissolve, forming bright purple solution

  • Purple solution is carried through water by convection, so traces out the path of convection currents in beaker

<ul><li><p>Place some <strong>purple </strong>potassium permanganate crystals in one side of beaker of <strong>cold water</strong></p></li><li><p>Using Bunsen burner, <strong>gently heat</strong> side of beaker with crystals at bottom</p></li><li><p>As <strong>temp </strong>of water around potassium permanganate crystals <strong>increases</strong>, they begin to <strong>dissolve</strong>, forming <strong>bright purple solution</strong></p></li><li><p>Purple solution is <strong>carried </strong>through water by <strong>convection</strong>, so <strong>traces out </strong>the path of <strong>convection currents</strong> in beaker</p></li></ul>
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29

Investigating thermal radiation

  • Place an empty Leslie cube (its four vertical faces have different surfaces) on heat-proof mat

  • Boil water in kettle and fill Leslie cube with boiling water

  • Wait a while for cube to warm up, then hold thermometer against each of four vertical faces of cube
    All four faces should be same temp

  • Hold IR detector a set distance (e.g. 10cm) away from one of cube’s vertical faces, and record amount of IR radiation detected

  • Repeat measurement for each of cube’s vertical faces
    Make sure detector is same distance from cube each time

  • More IR radiation should be detected from black surface than white, and more from matt than shiny

  • Repeat experiment for reliability

<ul><li><p>Place an <strong>empty Leslie cube</strong> (its four <strong>vertical faces</strong> have <strong>different surfaces</strong>) on <strong>heat-proof </strong>mat</p></li><li><p><strong>Boil </strong>water in kettle and <strong>fill Leslie cube </strong>with boiling water</p></li><li><p>Wait a while for cube to <strong>warm up</strong>, then hold <strong>thermometer</strong> against each of four vertical faces of cube<br>All four faces should be <strong>same temp</strong></p></li><li><p>Hold <strong>IR detector </strong>a <strong>set distance</strong> (e.g. 10cm) away from one of cube’s vertical faces, and record <strong>amount of IR radiation</strong> detected</p></li><li><p><strong>Repeat</strong> measurement for <strong>each</strong> of cube’s <strong>vertical faces</strong><br>Make sure detector is <strong>same distance</strong> from cube each time</p></li><li><p><strong>More IR radiation</strong> should be detected from <strong>black</strong> surface than <strong>white</strong>, and more from <strong>matt</strong> than <strong>shiny</strong></p></li><li><p><strong>Repeat </strong>experiment for <strong>reliability</strong></p></li></ul>
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Reducing rate of thermal energy transfer

  • Reduce conduction by using materials with low thermal conductivity

  • Reduce convection by stopping fluid from moving and preventing convection currents from forming

  • Reduce radiation by designing object with surface that is poor emitter, e.g. shiny and white

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Insulation

such as clothes, blankets, foam cavity wall insulation, work by trapping pockets of air

Air can’t move so energy has to conduct very slowly through air pockets, as well as material in between, both of which have low thermal conductivity

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Equation: Work done, Force and Distance

W = Fd

Work done = Force x Distance moved

[J] = [N] x [m]

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Work done =

energy transferred

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Equation: Gravitational potential energy

GPE = mgh

Gravitational potential energy = Mass x Gravitational field strength x Height

[J] = [kg] x [N/kg] x [m]

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Equation: Kinetic energy

KE = ½mv²

Kinetic energy = ½ x Mass x (Speed)²

[J] = ½ x [kg] x ([m/s])²

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36

Falling objects transfer energy

When something falls, energy from GPE store is transferred to its KE store

For a falling object when there’s no air resistance:
Energy lost from GPE store = Energy gained in KE store

Related to Principle of Conservation of Energy

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Power

Rate of transfer of energy

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Equation: Power, Work done and Time

P = W/t

Power = Work done / Time taken

[W] = [J] / [s]

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39

Non-renewable energy sources

  • They will all run out one day

  • They all damage environment

  • But provide most of our energy

  • Sources

  • Coal

  • Oil

  • Natural gas

  • Nuclear fuels

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Fossil fuel power stations

  • As fossil fuel burns (in oxygen), energy in chemical energy store is transferred to thermal energy store of water by heating

  • Water boils to form steam, which turns a turbine, transferring energy mechanically to KE store of turbine

  • As turbine revolves, so does the generator, producing electric current
    Generator transfers energy electrically away from power station, via national grid

<ul><li><p>As fossil fuel <strong>burns</strong> (in oxygen), energy in <strong>chemical energy store</strong> is transferred to <strong>thermal energy store</strong> of water <strong>by heating</strong></p></li><li><p>Water <strong>boils </strong>to form <strong>steam</strong>, which <strong>turns</strong> a <strong>turbine</strong>, transferring energy <strong>mechanically </strong>to <strong>KE store</strong> of turbine</p></li><li><p>As turbine revolves, so does the <strong>generator</strong>, producing electric current<br>Generator transfers energy <strong>electrically</strong> away from power station, via <strong>national grid</strong></p></li></ul>
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Fossil fuels + and -

Advantages:

  • Releases a lot of energy, relatively cheaply

  • Energy from fossil fuels doesn’t rely on weather, like most renewable energy, so it’s reliable

  • Fossil fuel power stations are already built, so don’t need to spend money on new tech to use them

Disadvantages:

  • Release carbon dioxide into atmosphere, contributing to global warming + climate change

  • Burning coal + oil also releases sulfur dioxide, causing acid rain, which can harm trees + soils and can have impact on wildlife

  • Will eventually run out

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42

Nuclear reactors

  • Nuclear fission produces the heat to make steam drive turbines, rather than burning, so the boiler is different

  • During process, energy is transferred from nuclear energy stores to thermal energy stores by heating, then mechanically to KE stores, and finally transferred electrically to national grid

<ul><li><p><strong>Nuclear fission</strong> produces the <strong>heat</strong> to make <strong>steam</strong> drive <strong>turbines</strong>, rather than burning, so the boiler is different</p></li><li><p>During process, energy is transferred from <strong>nuclear</strong> energy stores to <strong>thermal </strong>energy stores by heating, then mechanically to <strong>KE </strong>stores, and finally transferred electrically to national grid</p></li></ul>
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43

Nuclear power + and -

Advantages:

  • Doesn’t produce greenhouse gases which contribute to global warming

  • Plenty of uranium left in the ground

Disadvantages:

  • Nuclear reactors are expensive to build + maintain, and take longer to start up than fossil fuel ones

  • Processing uranium before use causes pollution, and risk of leaks of radioactive material

  • Radioactive waste

  • When they’re old and inefficient, nuclear power stations must be decommissioned (expensive)

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44

Wind farms

  • Involves putting wind turbines in exposed places - like on moors, around coast or at sea

  • Wind turbines use energy from KE store of moving air to generate electricity
    Wind turns blades, which turn a generator inside

<ul><li><p>Involves putting wind turbines in <strong>exposed places</strong> - like on <strong>moors</strong>, around <strong>coast</strong> or <strong>at sea</strong></p></li><li><p>Wind turbines use energy from <strong>KE </strong>store of moving air to generate electricity<br>Wind turns <strong>blades</strong>, which turn a <strong>generator </strong>inside</p></li></ul>
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Wind power + and -

Advantages:

  • Cheap to run

  • Tough and reliable

  • Wind is free

  • Doesn’t produce polluting waste

  • Renewable

Disadvantages:

  • Spoil the view

  • Inefficient - need 1500 wind turbines to replace one coal-fired power station

  • Can be very noisy - disturbance for local people

  • Sometimes wind isn’t strong enough to generate power

  • Expensive to set up wind farm, especially at sea

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46

Geothermal power

  • Only possible in certain places where hot rocks lie near the surface
    Source of most of the energy is slow decay of radioactive elements deep inside Earth

  • Water is pumped in pipes down to hot rocks and forced back up due to pressure to turn a turbine which drives a generator
    So energy is transferred from thermal energy stores to KE stores and used to generate electricity

<ul><li><p><strong>Only possible</strong> in <strong>certain places</strong> where <strong>hot rocks</strong> lie near the <strong>surface</strong><br>Source of most of the energy is <strong>slow decay</strong> of <strong>radioactive elements</strong> deep inside Earth</p></li><li><p><strong>Water is pumped </strong>in pipes down to <strong>hot rocks</strong> and forced back up due to <strong>pressure</strong> to turn a turbine which drives a <strong>generator</strong><br>So energy is transferred from <strong>thermal energy stores</strong> to <strong>KE stores</strong> and used to generate electricity </p></li></ul>
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47

Geothermal power + and -

Advantages:

  • Geothermal energy can be used to heat buildings directly

  • Free

  • Renewable

  • No environmental problems

Disadvantages:

  • Cost of drilling down several km

  • Cost of building power plant often high compared to amount of energy we can get from it

  • Few places where this is an economic option

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48

Solar cells

  • Solar cells use energy from Sun to directly generate electricity
    They generate direct current

<ul><li><p><strong>Solar cells</strong> use <strong>energy</strong> from Sun to directly generate electricity<br>They generate <strong>direct current</strong></p></li></ul>
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49

Solar cells + and -

Advantages:

  • Renewable

  • After initial costs, energy is free and running costs almost nothing

Disadvantages:

  • Very expensive initially

  • No pollution

  • Often too expensive or impractical to connect to national grid - cost of connecting to national grid can be huge compared to value of electricity generated

  • Can only generate enough electricity to be useful if they have enough sunlight - can be a problem at night

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50

Solar water heating panels

  • More simple than solar cells

  • Black water pipes inside glass box

  • Glass lets energy from Sun in, which is absorbed by black pipes and heats up water

<ul><li><p>More simple than solar cells</p></li><li><p><strong>Black water pipes</strong> inside <strong>glass </strong>box</p></li><li><p><strong>Glass</strong> lets <strong>energy </strong>from Sun in, which is <strong>absorbed </strong>by black pipes and heats up water</p></li></ul>
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Cooking with solar power

Can focus Sun’s light using curved mirror

<p>Can <strong>focus </strong>Sun’s light using <strong>curved mirror</strong></p>
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52

Solar heating systems + and -

Advantages:

  • Renewable

  • Free after setup cost

Disadvantages:

  • Solar water heating is only for small-scale energy production

  • Solar ovens are slow, bulky and unreliable - need strong sunlight to work

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53

Wave power

  • Lots of small wave converters located around coast
    As waves come in to shore, they provide up and down motion which can be used to drive generator

  • Energy is transferred from KE store of waves to KE store of turbine, and used to generate electricity

<ul><li><p>Lots of small <strong>wave converters </strong>located <strong>around coast</strong><br>As waves come in to shore, they provide <strong>up and down motion</strong> which can be used to drive <strong>generator</strong></p></li><li><p>Energy is transferred from <strong>KE store</strong> of waves to <strong>KE </strong>store of turbine, and used to generate electricity</p></li></ul>
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54

Wave power + and -

Advantages:

  • No pollution

  • Renewable

  • No fuel costs + minimal running costs

Disadvantages:

  • Spoils view

  • Hazard to boats

  • Fairly unreliable, as waves usually die out when wind drops

  • High initial cost

  • Can’t be used on large scale, but can be useful on small islands

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55

Tidal barrages

  • Big dams built across river estuaries, with turbines in them

  • As tide comes in, it fills estuary to height of several metres

  • Water can be allowed out through turbines at controlled speed

  • Energy is transferred from KE stores of water to KE store of turbine, and used to generate electricity

<ul><li><p><strong>Big dams</strong> built across<strong> river estuaries</strong>, with <strong>turbines</strong> in them</p></li><li><p>As <strong>tide comes in</strong>, it fills estuary to height of <strong>several metres</strong></p></li><li><p>Water can be allowed out through<strong> turbines</strong> at controlled speed</p></li><li><p>Energy is transferred from <strong>KE stores </strong>of water to <strong>KE store</strong> of turbine, and used to generate electricity</p></li></ul>
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Tidal barrages + and -

Advantages:

  • No pollution

  • Renewable

  • Fairly reliable

  • No fuel costs + minimal running costs

Disadvantages:

  • Prevents free access by boats

  • Spoils view

  • Alters habitat of wildlife

  • Height of tide is variable so lower tides provide less energy than higher ones

  • Moderately high initial costs

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57

Hydroelectricity

  • Often requires flooding of valley by building a big dam

  • Rainwater is caught and allowed out through turbines, transferring energy from GPE store of water to KE stores as it falls, which is used to generate electricity

<ul><li><p>Often requires <strong>flooding</strong> of <strong>valley</strong> by building a <strong>big dam</strong></p></li><li><p><strong>Rainwater</strong> is caught and allowed out <strong>through turbines</strong>, transferring energy from <strong>GPE store </strong>of water to <strong>KE stores </strong>as it falls, which is used to generate electricity</p></li></ul>
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Hydroelectric power + and -

Advantages:

  • Renewable

  • No pollution

  • Immediate response to increased demand - if more energy is needed than national grid can supply, water is released

  • Reliable

  • No fuel costs + low running costs

Disadvantages:

  • Big environmental impact due to flooding valley (rotting vegetation releases greenhouse gases) and possible loss of habitat for some species

  • Reservoirs can look bad when they dry up

  • High initial costs

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Pumped storage

  • Most large power stations have huge boilers which must be kept running all night even though demand is very lowsurplus of electricity at night - very difficult to keep spare energy for later use

  • ‘Spare’ night-time electricity is used to pump water up to a higher reservoir

  • This can be released quickly during periods of peak demand, such as evenings, to supplement the steady delivery from big power stations

  • ‘Spare’ electricity is used to transfer energy back to water’s GPE stores, so it can generate more electricity when needed by flowing through dam

<ul><li><p>Most large power stations have <strong>huge boilers</strong> which must be kept running <strong>all night</strong> even though demand is <strong>very low</strong> → <strong>surplus </strong>of electricity at night - very <strong>difficult </strong>to <strong>keep </strong>spare energy for <strong>later use</strong></p></li><li><p>‘Spare’ <strong>night-time electricity</strong> is used to pump water up to a <strong>higher reservoir</strong></p></li><li><p>This can be <strong>released quickly</strong> during periods of <strong>peak demand</strong>, such as evenings, to supplement the <strong>steady delivery</strong> from big power stations</p></li><li><p>‘Spare’ electricity is used to transfer energy back to water’s <strong>GPE stores</strong>, so it can generate more electricity when needed by flowing through dam </p></li></ul>
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