Transcript Topic 8: Energy, Power and Climate Change

Topic 8: Energy, Power and
Climate Change
Nina
8.1 Energy degradation and power
generation
• Continuous conversion of energy requires a
cyclical process
• Degraded energy: transferred to the
surroundings and no longer available
• Sankey diagrams
• Basic idea of a power station – rotating coils in
magnetic fields
Sankey diagrams
8.2 World energy sources
Percentage use
Gas
24%
Nuclear
6%
Coal
25%
Biomass
4%
Other
8%
Hydroelectric
3%
Oil
37%
Other
1%
Energy density
• Energy density (J kg-1) =
(energy released from fuel [Joules])/(mass of
fuel used [kg]) (not given in DB)
• Discuss how this influences the choice of fuel
• Also know all but a few sources of energy
originate in the sun somehow
Efficiency of fossil fuels
Maximum Efficiency
60%
50%
40%
30%
20%
10%
0%
Maximum Efficiency
Coal PS
42%
Oil PS
45%
Gas PS
52%
Nuclear power
• You know the general idea
• Fuel enrichment: increasing the proportion of
U-235
• Fissionable: can undergo nuclear fission
• Fissile: fissionable by low KE neutrons
• Moderator (eg water): slows neutrons down
• Control rod (eg boron): absorbs neutrons
Nuclear power (2)
• Know that U-235 fission results in neutrons
that can be captured by U-238, which decays
into Pu-239 which can then be used as fuel in
other reactors
• Know general risks/ethical issues (controlled
power station vs chain reaction/bomb)
• Know why we can’t (yet) do nuclear fusion
Solar power
• Photovoltaic cell (PV): produces electrical
energy
• Solar panel: produces thermal energy
• Know of seasonal/regional variations in solar
power (further from the equator, less intense
power)
Hydroelectric power
• GPE -> KE (water) ->KE (turbines) -> electrical E
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Lake/dams version (“water storage in lakes”)
Tidal version (“tidal water storage”)
Pumping version (“pump storage”)
Know the three different schemes
Wind power
• Know basic features (nacelle with generator,
rotor blades)
• Power delivered= ½ A 𝜌 v3
• A = area swept by blades (ᴨr2)
• 𝜌 = density of air
• v = wind velocity
Wave power
• Oscillating water column (OSW)
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• Power = ½ A2 𝜌 g v
A = wave amplitude
𝜌 = water density
g = gravity
v = wave velocity
Greenhouse effect
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Inverse square law: I = power/A
I: Intensity
Power of source
Area of sphere around source (4ᴨr2)
• Albedo: proportion of energy reflected compared to
the total energy received (equation given in data
book). Know relative snow/ocean albedo
• Average earth albedo: 30%
Greenhouse gases
• Methane, water vapour, carbon dioxide,
nitrous oxide (natural and man-made origins)
• Resonance between gases’ natural frequency
of oscillation and infrared emitted by Earth
• Gases ‘trap’ infrared and reemit it in all
directions (among which back to Earth)
Black body radiation
• Absorbs all radiation and reflects none: black
when cold.
• When hot emits radiation at all wavelengths.
‘Perfect’ emitter.
• Power emitted by a black body = σAT4
• σ: Stefan-Boltzmann constant (5.67 x10-8 Wm-2K4)
• A: surface area of the emitter
• T: temperature of the emitter (K)
Emissivity (e)
• How well a surface emits radiation
• Between 0 and 1. Perfect emitter has
emissivity of 1
• -> power emitted by any body = eσAT4
Surface heat capacity
• Measurement of how much energy is required
to heat up 1 m2 of a surface by 1°C
• Cs= Q/AΔT
• Cs: surface heat capacity
• Q: energy necessary
• A: land area
• ΔT: temperature difference
Global warming
• Change of a planet’s temperature over a
period of time:
• ΔT= [(Iin – Iout) Δt]/Cs
Global warming (2)
• International ice core research
• Coefficient of volume expansion
• International efforts:
– Intergovernmental Panel on Climate Change (IPCC)
– Kyoto Protocol
– Asia-Pacific Partnership on Clean Development
and Climate (APPCDC)
In conclusion: READ THE
SYLLABUS
http://gradegorilla.com/IBclimate/cli
mate1.php