Energy Science Fundamentals PDF

Lecture 2 Energy Science Fundamentals EMAN 204 1 Lecture 2  Source Resource Energy end use Solar PV Wind Wave Hydro Solar Biomass Electricity ra...

Lecture 2 Energy Science Fundamentals EMAN 204 1 Lecture 2  Source Resource Energy end use Solar PV Wind Wave Hydro Solar Biomass Electricity radiation Coal Oil Mechanical Includes motion transport Gas Solar thermal Heat/Pressure Nuclear Nuclear decay Geothermal Moon’s gravitational Tidal pull EMAN 204 4 Lecture 2 EMAN 204 5 Lecture 2 Units Force newtons – F= m a, Units: [N]=[kg] [m]/[s]2 Energy joules, watt-hours, kWh, MWh etc 1 – Kinetic energy: 𝐾𝐸 = 𝑚𝑣 2 , Units: [J]=[kg] [m/s]2 2 – Work: 𝑊 = 𝐹𝑥, (force times distance) Units: [J]=[Nm]= [kg] [m]2/[s]2 Power watts = joules/sec- kW, MW 𝑑𝑊 𝑑𝑥 – Rate of change of work: = 𝐹 = 𝐹𝑉 Units [W]=[J]/[s] = 𝑑𝑡 𝑑𝑡 [N][m]/[s]=[kg] [m]2/[s]3 Temperature (kelvin) – degrees Celsius/kelvin (0°C = 273 K) EMAN 204 7 Lecture 2 Some common units of energy Unit Abbreviation Value in kJ Joule J 0.001 Kilowatt-hour kWh 3600 British thermal unit Btu 1.055 Kilocalorie kcal 4.184 Tonne of oil equivalent toe 41,868 Electron-volt eV 1.6 x 10-12 EMAN 204 8 Big Numbers - prefixes Prefix Example Kilo x103 (Thousand) Rooftop solar PV panels 2- 3.5 kW under full sun Mega x106 (Million) A utility scale wind turbine: 2 MW Giga x109 (Billion) Huntly power station: 0.9 GW NZ electricity consumption ~5 GW Tera x1012 (Trillion) NZ annual electricity consumption ~40 TWh Peta x1015 NZ consumes about 600 PJ/year Exa x 1018 World consumes about 500 EJ/year EMAN 204 9 Lecture 2 Energy Science: Energy vs Power Energy Δ𝐸 Energy Measured in joules (J or kWh) 1 litre of petrol: 32,000,000 J= Δ𝑡 32 MJ Time Energy to boil 1 litre of water: 2,260 kJ Δ𝐸 𝑑𝐸(𝑡) Power: gradient of a 𝑃(𝑡) = lim = ∆𝑡→0 Δ𝑡 𝑑𝑡 energy vs time curve Power = Rate of energy production or use Power Measured in watts (W)=joules/second Toaster 700 W Time ti tf 𝑡𝑓 Energy: area under a 𝐸 𝑡𝑓 − 𝐸(𝑡𝑖 ) = න 𝑃 𝑡 𝑑𝑡 𝑡𝑖 power vs time curve EMAN 204 10 Lecture 2 Mass balance 𝑚ሶ 𝑖𝑛 𝑑𝑚𝑐𝑣 Rate of change 𝑚ሶ 𝑜𝑢𝑡 in mass in Mass flow 𝑑𝑡 Mass flow system (kg/s) into system out of system (kg/s) (kg/s) System (Control volume) Boundary 𝑑𝑚𝑐𝑣 Mass balance: = 𝑚ሶ 𝑖𝑛 − 𝑚ሶ 𝑜𝑢𝑡 𝑑𝑡 Steady state: No change in mass in the system Mass flow in = mass flow out 𝑑𝑚𝑐𝑣 𝑚ሶ 𝑖𝑛 = 𝑚ሶ 𝑜𝑢𝑡 =0 𝑑𝑡 EMAN 204 12 Lecture 2 Energy balance 𝑃𝑖𝑛 𝑑𝐸𝑐𝑣 Rate of change 𝑃𝑜𝑢𝑡 in energy in Energy flow 𝑑𝑡 Energy flow system (J/s) into system out of system (J/s) (J/s) System (Control volume) Boundary 𝑑𝐸𝑐𝑣 Energy balance: = 𝑃𝑖𝑛 − 𝑃𝑜𝑢𝑡 𝑑𝑡 𝑃𝑖𝑛 and 𝑃𝑜𝑢𝑡 are energy flows (in J/s or W) or power into and out of control volume. Could be heat, work or energy associated with mass flow (e.g. thermal, kinetic, or potential energy) EMAN 204 13 Lecture 2 Energy balance 𝑃𝑖𝑛 𝑑𝐸𝑐𝑣 Rate of change 𝑃𝑜𝑢𝑡 in energy in Energy flow 𝑑𝑡 Energy flow system (J/s) into system out of system (J/s) (J/s) System (Control volume) Boundary 𝑑𝐸𝑐𝑣 Energy balance: = 𝑃𝑖𝑛 − 𝑃𝑜𝑢𝑡 𝑑𝑡 Steady state: No change in energy in the system Energy flow in = energy flow out 𝑑𝐸𝑐𝑣 𝑃𝑖𝑛 = 𝑃𝑜𝑢𝑡 =0 𝑑𝑡 EMAN 204 14 Lecture 2 Energy efficiency Many processes involve conversion of energy from one form into another. Usually some energy will be “lost” as a form that is not useful to us (e.g. heat). Useful energy out Energy efficiency = Energy input EMAN 204 16 Efficiency of energy conversion Steady-state conversion process 𝑃𝑙𝑜𝑠𝑠 No change in system 𝑃𝑜𝑢𝑡 𝑃𝑖𝑛 energy System Boundary Energy balance: 0 = 𝑃𝑖𝑛 − 𝑃𝑜𝑢𝑡 − 𝑃𝑙𝑜𝑠𝑠 Efficiency: 𝑃𝑜𝑢𝑡 𝑃𝑖𝑛 − 𝑃𝑙𝑜𝑠𝑠 𝑃𝑙𝑜𝑠𝑠 𝜂= = =1− 𝑃𝑖𝑛 𝑃𝑖𝑛 𝑃𝑖𝑛 EMAN 204 17 Lecture 2 Energy efficiency Energy is lost at each step of an energy system: – Extraction of the natural resource – the primary energy (e.g. coal from a mine, wind by a turbine). – Conversion into a useful form of energy (e.g. electricity generation, refining oil into fuels). – Transmission / transport to the end user (e.g. via power lines, pipelines or tanker). – Consumption of energy, i.e. conversion to the final desired form (e.g. electricity into light; fuel into motion). EMAN 204 22 Typical energy efficiencies Modern coal power station 40% Nuclear power station 30% Modern gas power station (CCGT) 55% Geothermal power station 10% Wind turbine 40% Solar photovoltaic panel 20% Concentrated solar power station 20% Solar thermal panel 50% Internal combustion engine 25% EMAN 204 23  Electricity generation Electricity transmission LED bulb Transmission losses: 4 J Electricity: Waste heat: Electricity 40 J 29 J delivered: 36 J Coal in: Light: 7 J 100 J Waste heat: 60 J EMAN 204 24  Oil Refining Internal Combustion Engine Motion: Vehicle 21 J motion: 20 J Gasoline: 85 J Crude oil: 100 J Waste heat: 64 J Refinery losses: 15 J EMAN 204 25  Oil Refining Internal Combustion Vehicle Engine Human motion: 1 J Motion: Vehicle 21 J motion: 20 J Gasoline: 85 J Crude oil: 100 J Waste heat: 64 J Refinery losses: 15 J EMAN 204 26  Source Resource Energy end use Solar PV Wind Wave Hydro Solar Biomass Electricity radiation Coal Oil Mechanical motion Gas Solar thermal Heat/Pressure Nuclear Nuclear decay Geothermal Moon’s gravitational Tidal pull EMAN 204 27 Lecture 2  Mechanical to Electrical: How a generator works (1) (2) (4) (3) Source: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/genhow.html#c1 EMAN 204 28 Lecture 2  Electrical to Mechanical: How an electrical motor works (1) (2) (3) ሶ 𝜏𝜔 𝑊= Mechanical work is given by torque times rotation rate Source: http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/mothow.html#c1 EMAN 204 29 Lecture 2 Summary Energy can be converted from one form to another but not destroyed Control volume analysis – application of 1st law. Efficiency: Energy out Power out h= = Energy in Power in Physical laws place restrictions on efficiency of energy conversion (will see more of this) EMAN 204 32 Lecture 2 Homework - Wind Which country has the highest installed wind capacity per capita? What percentage of electricity does wind power supply in that country? EMAN 204 34 Lecture 2