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

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

Nuclear power You know the general idea Fuel enrichment: increasing the proportion of U-235 Fissionable: can undergo nuclear fission Fissile: fissionable by low K E 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 -> K E (water) ->K E (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 v 3 A = area swept by blades (ᴨr 2 ) = density of air v = wind velocity

Wave power Oscillating water column (OSW) Power = ½ A 2 g v A = wave amplitude = 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 (4ᴨr 2 ) 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 = σAT 4 σ: Stefan-Boltzmann constant (5.67 x10 -8 Wm -2 K - 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 = eσAT 4

Surface heat capacity Measurement of how much energy is required to heat up 1 m 2 of a surface by 1°C C s = Q/AΔT C s : 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= [(I in – I out ) Δt]/C s

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)

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