Physics - P1.4 - Generating Electricity

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P1.4.1 - Fuel for Electricity

  • Most power stations - water heated to produce steam -> steam drives a turbine, coupled to an electrical generator that produces electricity
  • Energy from burning fossil fuels - long-dead biological material
  • Some gas-fired power stations - hot gas power drive turbine - switched on/off quickly
  • Biofuel - fuel obatained from (recently) living organisms - used in small scale gas-fired power stations - renewable
  • Nuclear power station - uranium(/plutonium) used as fuel - uranium atom can undergo nuclear fission - releases lots of energy - lots of uranium nuclei = lots of fission reactions - energy used to heat water -> steam
  • Energy released/kg in nuclear power station > energy released/kg in gas-fired power station
  • Nuclear power stations - no greenhouse gases, radioactive waste
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P1.4.2 - Energy from Wind and Water

  • Renewable energy - never be used up
  • Use energy from wind and water to drive turbines directly
  • Wind - wind passes over blades -> rotate -> drive generator
  • Water - obtained from falling water, waves or tides, hydroelectric power - water collected in a reservoir -> water flows downhill -> turns turbines -> times of low demand, surplus electricity used to pump water back to top - energy is stored
  • Wave - movement of waves on sea used to generate electricity - movement drivesfloating turbine -> turns generator -> electricity delivered to grid system by onshore cable
  • Tidal - barrage built across river estuary -> water at high tide trapped behind it -> released to fall to lower sea -> drives turbines
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P1.4.3 - Power from the Sun and the Earth

  • Solar energy - travels from sun to earth as electromagnetic radiation
  • Solar cell - transfer sun energy -> electrical energy, each cell only produces small amount of energy - useful to power small devices (eg. watches, calculators), can join large numbers together to form solar panel
  • Water heated directly by sun as it flows through solar heating panel
  • Solar power tower - uses thousands of mirrors to reflect sunlight onto water tank to heat water -> steam
  • Geothermal energy - produced instide the earth by radioactive processes - heats surrounding rock - in volcanic areas, deep holes drilled -> cold water pumped down to hot rocks -> heated -> returns to surface as steam -> drive turbines that turn generators
  • In few parts of the world - hot water comes to surface naturally - used to heat nearby buildings
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P1.4.4 - Energy and the Environment

  • Coal, oil, gas and uranium - non-renewable - rate they are being used > rate they are being produced
  • Oil and gas - run out in ~50 years, coal will last longer
  • Renewable energy sources - won't run out - can be produced as fast as they're used
  • Scientists investigating ways to reduce environmental impact of using fossil fuels - eg. sulfur removed from fuel before burning, capturing CO2 and storing in old oil and gas fields, instead of releasing it into atmosphere
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P1.4.4 - Different Energy Resources

  • Coal - bigger reserve, reliable, non-renewable, produces CO2 and SO2
  • Oil - reliable, non-renewable, produces CO2 and SO2
  • Gas - reliable, non-renewable, produces CO2
  • Nuclear - no polluting gases, reliable, non-renewable, hazardous nuclear waste, (small) risk of nuclear accident
  • Wind - renewable, no polluting gases, free, requires turbines, not reliable
  • Falling water - renewable, no polluting gases, free, reliable where wet, only works in certain areas, damming - floods and affects local ecology
  • Waves - renewable, no polluting gases, free, reliable, few suitable areas, building barrages affects local ecology
  • Solar - renewable, no polluting gases, free, reliable, need many solar cells
  • Geothermal -  renewable, no polluting gases, free, economically viable in few places, drilling is difficult and expensive
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P1.4.5 - The National Grid

  • National Grid - dristributes electricity in Britain, network of pylons and cables that connect power stations to homes, schools, factories and other buildings, whole country connected - power stations switched in/out of grid according to demand
  • Cables carried over long distances in countryside, supported by overhead pylons, in towns - cables buried underground
  • National Grid voltage - 132000V, power station electricity - 25000V
  • Step-up transformers - increase voltage before electricity is transmitted across National Grid - transmission at high voltage = decreased wasted energy = efficient system
  • Step-down transformers - reduces voltage (230V) to be sent into homes - dangerous to supply electricity at high voltages
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P1.4.6 - Big Energy Issues

  • Constant amount of electricity provided by nuclear, coal- and oil-fired power stations - base load demand
  • Electricity demand varies over summer and winter (heating)
  • Variable demand met using gas-fired power stations, pumped storage schemes and renewable energy resources
  • Low demand - energy stored by pumping water to top of reservoir of pumped storage schemes
  • Start up times - different for each power station - gas-fired have shortest -> oil -> coal -> nuclear power stations have longest
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