Renewable and Non-Renewable Energy Sources: Comparison and Analysis, Study notes of Physics

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TOPIC 8 ENERGY PRODUCTION ENERGY SOURCES PRIMARY SOURCES: all types of unprocessed energy sources that can be found in nature SECONDARY SOURCES: processes / exploited to mechanical work / electrical forms EG: electricity RENEWABLE SOURCES: readily replenished - a fuel that is creased faster / equally fast as it is consumed EG: solar energy / wind energy NON-RENEWABLE SOURCES: a fuel that is consumed faster than it is created - will be depleted EG: fossil fuels / nuclear fuel RENEWABLE ENERGY SOURCES NON-RENEWABLE ENERGY SOURCES ● solar power ● wind power ● hydroelectric power ● tidal power ● geothermal ● biomass ● coal ● oil ● natural gas ● nuclear power SPECIFIC ENERGY (Es): amount of energy that can be extracted from a unit mass of fuel ⇒ energy / mass ENERGY DENSITY (Ed): amount of energy that can be extracted from a unit volume of fuel mass ⇒ energy / volume FUEL SPECIFIC ENERGY (Es) J kg¯¹ ENERGY DENSITY (Ed) J m¯³ uranium - 235 7.0 x 10¹³ 1.3 x 10¹⁸ hydrogen 1.4 x 10⁸ 1.0 x 10⁷ natural gas 5.4 x 10⁷ 3.6 x 10⁷ gasoline 4.6 x 10⁷ 3.4 x 10¹⁰ kerosene 4.3 x 10⁷ 3.3 x 10¹⁰ diesel 4.6 x 10⁷ 3.7 x 10¹⁰ coal 3.2 x 10⁷ 7.2 x 10¹⁰ SANKEY DIAGRAMS: show the energy transfer & loss ⇒ width of each arrow is proportional to the amount of energy transfer ENERGY DEGRADATION ● while energy may be completely converted into work in a single process, a CYCLICAL PROCESS is required to convert thermal energy to work continuously ● in accordance with the 2ND LAW OF THERMODYNAMICS, some energy will be lost to the surroundings & cannot be used to perform useful work DEGRADED ENERGY: unavailable energy FOSSIL FUELS: produced by the decomposition of buried animals & plant material due to pressure & bacteria EG: oil / coal / natural gas ADVANTAGES DISADVANTAGES + ↑ power output ⇒ ↑ energy density + large reserves of nuclear fuels + nuclear power stations do not produce ghgs - radioactive waste products are difficult to dispose of - major public health hazard should ‘something go wrong’ - problems associated with uranium mining - possibility of producing materials for nuclear weapons SOLAR POWER SOLAR PANELS: collect heat from the Sun which is used to heat the H₂O in pipes underneath ● flat collecting surface ● coating: ↓ reflection ● black surface below collects sunlight which heats up the H₂O in the pipe underneath for use in the house ADVANTAGE: cheap DISADVANTAGE: bulky PHOTOVOLTAIC CELLS: convert light directly into electricity ● sunlight incident on photovoltaic cell makes the e¯ excited ⇒ establish a potential difference ADVANTAGES DISADVANTAGES + ‘free’ + inexhaustible + clean - ↓ power output - works during the day only - affected by cloudy weather - ↓ power output - requires large area - initial $$ ↑ HYDROELECTRIC POWER: power derived from moving masses of H₂O ● H₂O falls from a reservoir down to a power station ⇒ PE to KE ● the falling H₂O passes through turbines ⇒ KE to electric energy * when energy is not in demand (eg: during the night), the H₂O can be pumped back up PUMPED STORAGE SYSTEM PEAK HOURS: power plant produces energy - H₂O falls OFF-PEAK HOURS: power plant consumes electricity - H₂O pumped back up ● efficiency is not 100% ⇒ need more energy to pump up than is produced ● during off-peak hours, cheap electricity is used from elsewhere ⇒ demand is ↓ ● energy ‘stored’ in the form of GPE for use at peak times ADVANTAGES DISADVANTAGES + ‘free’ + inexhaustible + clean - very dependent on location - requires drastic changes to the environment causing local ecology - initial $$ high WIND POWER: power derived from moving masses of air ⇒ typically ∼30% of the power carried in wind is converted to energy BIGGEST LOSS OF EFFICIENCY: wind cannot be stopped completely by the turbine ⇒ not all KE is transferred ADVANTAGES DISADVANTAGES + ‘free’ + inexhaustible + clean - dependent on local wind conditions - aesthetic problems - large infrastructures - noise problems 1. mass of air = ƿAvΔT 2. KE of air = ½mv² = ½ƿAvΔtv² = ½ƿAΔtv³ 3. power = E/Δt = ½ƿAv³ THERMAL ENERGY TRANSFER CONDUCTION: transfer of energy due to ↑ energy e¯ colliding with neighbouring molecules CONVECTION EG: air over a hot radiator in a room is heated, expands & rises, transferring warm air to the rest of the room - cold air takes its place through convection currents & the process repeats RADIATION: transfer of energy through electromagnetic induction BLACK-BODY RADIATION ● all bodies with a finite (Kelvin) T°C radiate energy in the form of EM radiation (due to oscillating electric charges) STEFAN-BOLTZMAN LAW ENERGY BALANCE ● at EQUILIBRIUM, the energy input must be equal to the energy output ● the effects of the Earth's atmosphere on its mean surface T°C ⇒ GREENHOUSE EFFECT TEMPERATURE AT EARTH’S SURFACE 1) the Earth radiates power from the entire surface area of its spherical shape, so the power radiates is: 2) assume the Earth is a black body ⇒ 𝜺 = 1 3) equating the incident & outgoing intensities, we get: 4) solving the equation, we get: 5) T = -17°C * actual average T°C of the Earth surface = 288K / 15°C THE GREENHOUSE EFFECT GREENHOUSE GASES: CO₂ / CH₄ / H₂O / N₂O ⇒ found in the Earth’s atmosphere ⇒ both natural & man-made origins ● by using WIEN’S DISPLACEMENT LAW with T=288K, we find that the peak 𝝺 that is radiated by the Earth is in the INFRARED REGION ● infrared radiation is STRONGLY ABSORBED by greenhouse gases ○ e¯ transition between the MOLECULAR ENERGY LEVELS ○ the energy difference corresponds to energy of photons with infrared 𝝺 ● the absorbed radiation is eventually RE-RADIATED IN ALL DIRECTION ⇒ some of the re-radiated energy is absorbed by the Earth again causing the surface to be warmer GREENHOUSE GAS NATURAL SOURCES ANTHROPOGENIC SOURCES H₂O evaporation of H₂O from oceans / rivers / lakes irrigation O₂ forest fires / volcanic eruptions / evaporation of H₂O from oceans burning fossil fuels in power plants & cars / burning forests CH₄ wetlands / ocean / lakes & rivers / termites flooded rice fields / farm animals / processing of coal / natural gas & oil / burning biomass N₂O forests / oceans / soil & grasslands burning fossil fuels / manufacture of cement / fertilisers / deforestation (↓ of nitrogen fication in plants)