Energy, power and climate change Great website

8.1 Energy degradation and power generation 1. Hot gas will cause the piston to move. Thermal energy may be completely converted to work in a single process 2.But one stroke of the piston does not provide much energy. Continuous conversion of this energy into work requires a cyclical process and this involves the transfer of some energy from the system. This is called DEGRADED ENERGY and is not available to do useful work SANKEY Diagram – 25% efficient – note the degraded energy – brown arrows

Production of electrical power 1.Heat source 2.Steam generation 3.Turbines 4.Generator 5.Transmission lines Hyperlink Electrical energy is produced by coils rotating in a magnetic field.

World use of energy sources 91% Non- renewable Oil, Coal, Gas, - emit CO 2 Nuclear. The SUN is the prime energy source for world energy. Only approximate values are needed

Energy density of fuels: The amount of energy that can be extracted per Kg of Fuel – influences choice of fuel Energy in MJ/Kg Nuclear/Uranium 90,000,000 Crude Oil 42 Coal Wood 17 Gas 54 NOTE: The energy density values will be provided in the questions on the paper.

8.3 Fossil fuel power production Industrialization in the 19 th century led to a higher rate of energy usage, leading to industry being developed near to large deposits of fossil fuels. Efficiency Coal 35 – 42% Natural Gas 45 – 52% Oil 38 – 45% Advantages – easy to transport, used in home for heating, cheap in comparison with other sources. Disadvantages – coal fired stations need large amounts of fuel, pollution – acid rain, greenhouse gases, oil spills and fires, mining dangers for health.

Nuclear power Each fission reaction releases neutrons that are used in further reactions when slowed down: low-energy neutrons (≈ 1 eV) cause further fission leading to a chain reaction. Fast neutrons Critical mass: minimum mass required for a sustained chain reaction

Controlled nuclear fission (power production) Uncontrolled nuclear fission (nuclear weapons). Natural U-235 (used for fission) occurs as 0.7% abundance (99.3% U-238) Enriched fuel contains 2.3% U-235, used in power production and increases the efficiency and power output/Kg of nuclear reactors.

graphite moderator boron control rod heat exchanger fuel element channel steel concrete hot gas reactor core cold gas charge face The moderator slows the neutrons down to enable them to allow further fission The control rods absorb neutrons to control the power level The heat exchanger isolates the water from the coolant and lets the hot gas boil the water. E K Fission fragments -> heat (gas, then water) -> E K(turbines)

Fast breeder reactors using plutonium The U-238 can capture neutrons and is converted to Pu-239 The Pu-239 is fissionable by fast neutrons Therefore, the reactor can breed its’ own fuel Risks and safety issues: Meltdown – This is when the power goes out of control and the reactor blows up. This may happen if the coolant is “interrupted”, or the control rods are removed. The waste produced is radioactive, and is hazardous to living things. It is expensive to store. The half life of some products is very long. Uranium mining - Because uranium ore emits radon gas, uranium mining can be more dangerous than other underground mining.radon The plutonium produced can be used for weapons manufacture.

Nuclear fusion The plasma needs to be at a temperature of about 10 8 K and has a high density. It is difficult to confine and maintain the plasma. Can be contained by a magnetic field.

Solar power 1. photovoltaic cell (radiant to electrical) There are 2 types of solar power In a sunny climate, you can get enough power to run a 100W light bulb from just one square metre of solar panel. Good for remote situations. 2. Solar water heating The Sun is used to heat water in glass panels on the roof (radiant to thermal). This means you don't need to use so much gas or electricity to heat your water at home. Solar power received on earth is less if: You are not at the Equator It is not mid summer

Hydroelectric power RENEWABLE (PE to KE to Electrical energy water storage in lakes Advantages Once the dam is built, the energy is virtually free. No waste or pollution produced. Much more reliable than wind, solar or wave power. Water can be stored above the dam ready to cope with peaks in demand. Hydro-electric power stations can increase to full power very quickly, unlike other power stations. Electricity can be generated constantly Disadvantages The dams are very expensive to build. However, many dams are also used for flood control or irrigation, so building costs can be shared. Building a large dam will flood a very large area upstream, causing problems for animals that used to live there. Finding a suitable site can be difficult - the impact on residents and the environment may be unacceptable. Water quality and quantity downstream can be affected, which can have an impact on plant life.

Tidal water storage (PE to KE) Doesn't cause pollution, doesn't need fuel A tidal barrage is very expensive to build Only works when tide is going in or out A tidal barrage affects a large area There are very few places that you could sensibly build a Tidal barrage Underwater turbines may be a better bet than a barrage - they are cheaper and don't have the huge environmental impact Pump storage Electrical + PE to KE to electrical energy. It's a way of storing energy for when you need it in a hurry.

Wind power The wind blows the propeller around, which turns a generator to produce electricity Wind Power is renewable Doesn't cause pollution, doesn't need fuel Need a lot of generators to get a sensible amount of power Need to put them where winds are reliable. Energy = ½ mv 2 Mass per sec = ρ x volume = ρ x Area x speed = ρπr 2 v Energy/s = ½ ρπr 2 v x v 2 = ½ ρπr 2 v 3 The wind does not stop after passing through the turbine, therefore not all the energy can be harnessed (max = 59%)

Wave power (OWC) Hyperlink Energy can be extracted from waves in a number of waves including an Oscillating Water Column Advantages The energy is free - no fuel needed, no waste produced. Not expensive to operate and maintain. Can produce a great deal of energy. Disadvantages Depends on the waves - sometimes you'll get loads of energy, sometimes almost nothing. Must be able to withstand very rough weather Needs a suitable site, where waves are consistently strong. Volume of water in red area = a x λ/2 x L Mass = Volume x density(ρ) Number of waves per sec = v/λ Loss of GPE of the wave per sec = mgh = (a x λ/2 x L x ρ) x g x a x v/λ a λ L Power per unit length = ½ a 2 ρgv

Solar constant The sun radiates 3.9x10 26 W The Earth is a distance of 1.5x10 11 m from the sun Calculate the power per m 2 reaching the Earth. I = 3.9x10 26 W 4π(1.5x10 11 ) 2

albedo SurfaceTypical Albedo Fresh asphalt0.04 Conifer forest (Summer) 0.08,0.09 to 0.15 Worn asphalt0.12 Deciduous trees 0.15 to 0.18 Bare soil0.17 Green grass0.25 Desert sand0.40 New concrete0.55 Fresh snow0.80–0.90 The albedo also varies with factors like season latitude cloud cover The average value on Earth is 0.3

Greenhouse effect and greenhouse gases Short λ not absorbed Long λ absorbed Main greenhouse gases: water vapour, carbon dioxide, methane, N 2 O. Each has a natural - livestock and plants, and man made origin - Burning of fossil fuels, fertilisers and deforestation.

Molecular mechanisms: Absorption of IR radiation Carbon dioxide, water vapour, methane, nitrous oxide, and a few other gases are greenhouse gases. They all are molecules composed of more than two component atoms, bound loosely enough together to be able to vibrate with the absorption of heat. The resonant or natural frequency of greenhouse gases is in the IR region

Black-body radiation is the radiation emitted by a perfect emitter. λ max x T = Wien’s constant Stefan–Boltzmann law P = Power emitted from a surface. σ = Stefan–Boltzmann constant A = Surface area of emitting body T = Temperature of the emitter

Emissivity The Earth is not a perfect Black Body radiator (or absorber). The emissivity (e) is defined as Surface heat capacity (C s ) is the energy required to raise the temperature of unit area of a planet’s surface by one degree, and is measured in J m –2 K –1.

Climate change model The change of a planet’s temperature over a period of time is given by: (incoming radiation intensity – outgoing radiation intensity) × time / surface heat capacity. Predictions

Describe some possible models of global warming. A range of models has been suggested to explain global warming, including: Changes in the composition of greenhouse gases in the atmosphere. Increased solar flare activity. Cyclical changes in the Earth’s orbit. Volcanic activity. Hyperlink Enhancement of the greenhouse effect is caused by human activities. The generally accepted view of most scientists is that human activities, mainly related to burning of fossil fuels, have released extra carbon dioxide into the atmosphere.

Evidence of Global warming International ice core research produces evidence of atmospheric composition and mean global temperatures over thousands of years (ice cores up to 420,000 years have been drilled in the Russian Antarctic base, Vostok).

Some of the mechanisms that may increase the rate of global warming. Global warming reduces ice/snow cover, which in turn reduces the albedo, which increases the rate of heat absorption. It also increases evaporation. Temperature increase reduces the solubility of CO 2 in the sea and increases atmospheric concentrations Deforestation reduces carbon fixation and uptake of CO 2 The coefficient of volume expansion(γ) is the fractional change in volume (V) per degree change in temperature (T). γ=1/V o (ΔV/ΔT)

Possible reasons for a predicted rise in mean sea-level. Precise predictions are difficult to make due to factors such as: anomalous expansion of water different effects of ice melting on sea water compared to ice melting on land. One possible effect of the enhanced greenhouse effect is a rise in mean sea-level Climate change is an outcome of the enhanced greenhouse effect.

Possible solutions to reduce the enhanced greenhouse effect Greater efficiency of power production. Replacing coal and oil with natural gas. Carbon dioxide capture and storage. Use of hybrid vehicles. Increase use of renewable energy sources and nuclear power. Use of combined heating and power systems. International efforts: Intergovernmental panel on climate change. Kyoto protocol Asia-Pacific partnership on clean development and climate.