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

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 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 𝜌 v3 • A = area swept by blades (ᴨr2) • 𝜌 = density of air • v = wind velocity

Wave power • Oscillating water column (OSW) • Power = ½ A2 𝜌 g v • 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

Topic 8: Energy, Power and Climate Change