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

Oil37%

Coal25%

Gas24%

Nuclear6%

Biomass4%

Hydroelectric3%

Other1%

Percentage use

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

Coal PS Oil PS Gas PS0%

10%

20%

30%

40%

50%

60%

Maximum Efficiency

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

• 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 v𝜌 3

• A = area swept by blades (ᴨr2)• 𝜌 = density of air• v = wind velocity

Wave power

• Oscillating water column (OSW)

• Power = ½ A2 g v𝜌• A = wave amplitude• 𝜌 = water density• g = gravity• v = wave velocity

Greenhouse effect

• 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-2K-4)• 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/climate1.php