Living for the Future

Living for the Future

1. Solar Energy

   • Photocells
     • Robust, little maintainance
     • Solar fuel, no long cables
     • No pollituon
     • P-N silicon junction
       • P-type has absence of free electrons
       • N-type has excess free electrons
       • Photons excite electrons
         • Electric current produced
     • (-) No energy when dark/cloudy
     • Output:
       • Light intensity
       • Surface area
       • Distance from light source
     • DRAW OUT
   • Passive heating
     • Glass lets in shorter IR radiation
       • IR absorbed by walls and floor, heat up
         • IR re-emitted at longer wavelength
           • Glass reflects longer wavelength IR inside
   • Wind energy
     • Windspeed dependent
       • Will not work in too little/too much wind
     • No CO2
     • Noisy. take space, "NIMBY"

2. Generating Electricity

   • The Dynamo effect
     • Wire coil in a magnetic field = Current
       • Induced current
     • Increasing the effect:
       • Faster moving magnet
       • More wire coils
       • Stronger magnet
     • To reverse current:
       • Rotate magnet in opp. direction
       • Reverse magnet polarity
     • Either the coil OR the magnets can move
     • Always AC
     • DRAW OUT
   • Power Stations
     • Water boils to steam
       • High-pressure steam drives turbine
         • Turbine drives Generator
   • Energy Efficiency
     • Energy lost at each stage
     • Efficiency = Useful output / Total input

3. Global Warming

   • Most electromagnetic waves pass through atmosphere
     • IR absorbed at short wavelengths by Earth
       • Re-emitted at long wavelengths
         • Long wavelengths trapped
           • CO2
             • Volcanic eruptions
             • Forest fires
             • Organic decay
             • Oceans emit it
             • Respiration
   • Greenhouse Gases
     • Methane
       • Decay lacking oxygen
       • Wetlands, oceans
     • CO2
     • Water vapour = Most potent
       • Occurs naturally
   • Dust : Two effects
     • Factory smoke traps IR
       • Temp. Increases
     • Volcanic ash reflects IR
       • Temp. falls

4. Fuels for Power

   • Measuring power
     • Appliances use a certain amount of power per second
     • Power = Voltage x Current
       • Watts
     • Energy supplied = Power x Time
       • Kilowatt Hours (kWh)
   • Cost of Energy
     • Cost = Energy used x Cost per kWh
     • Often lower rates at night (off-peak)
   • Choices of Sources
     • Availability
     • Ease of extraction
     • Environmental effect
     • Risks associated
   • The National Grid
     • Transformers step up VOLTAGE to 400,000v
       • Transport electricity in powerlines
         • Transformers step down energy for consumer
     • High current heats up wires
       • Heat = Energy loss
         • Transformers allow higher [Voltage] and lower [Ampage]
           • Lowers energy lost
           • Keeps cost down
           • "When a transformer increases voltage, the ampage is reduced - Wires don't heat up, and therefore less energy is lost to the environment (sink)."
   • PRACTICE EQUATIONS

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