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Energy Units and Probability Laws

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Energy Units and Probability Laws Energy & Sustainability Lecture 3: Rules of the Game Energy units and conversion Factors And a few more words On probability January 20, 2009 Previous Class Summary reminder of last class . The laws of nature are absolute . Two ground rules concerning energy: ① Energy cannot be created or destroyed (1st law of TD) ② Conversion of high‐grade to low‐grade energy is irreversible and unavoidable (2nd law of TD) . Energy comes in many forms Before We Come to the Units A few more words for our dictionary • Primary energy: The total content of the original energy resource – Fossil fuels: coal, oil, and natural gas – Biofuels: wood, straw, dried dung etc. – Nuclear power – Renewable Energies: Geothermal and hydroelectric, solar and wind power Before We Come to the Units (2) A few more words for our dictionary • Renewable Energy: aka regenerative energies are those energy sources or energy carriers that are lasting/sustainable. They will be continually available within human timescales as opposed to fossil fuels and atomic fuel, which all came about only after millions of years of geological processes. • Geothermal energy cannot be counted as a regenerative energy source, but its use is equated with renewable energy. ??? Before We Come to the Units (3) A few more words for our dictionary • Energy consumption: Conversion of primary energy into heat, electrical energy, light, or into the kinetic energy of a moving vehicle Units • In 1960, agreement on a single set of units: the Système Internationale d’Unités – SI - Three main base units: m, kg, s - Derived units: • Speed: m/s • Energy: 1 J = 1 N x 1 m = 1 kg x m2/s2 • Everyday life: 1 J rather small quantity, roughly the amount needed to toss a mid‐size apple one meter vertically upwards • Other systems: tonnes or tons of oil or coal, cubic meters of gas, kilowatt‐hours, terrawatt‐years, therms, calories etc. Units • Large numbers: 103 106 109 1012 1015 1018 Units of power and energy . 1 W = 1 J/ 1 s . example: 600 W water heater is converting electrical energy into heat at a rate of 600 J in each second . 1 TW = 1 million million W = 1012 W . Example: we, the world population, with our consumption rate of ~ 16 TW , convert 16 trillion joules of primary energy every second into forms of energy we want ( + waste heat) . 1 kWh is the amount of energy converted in one hour at a rate of one kilowatt . 1 kWh = ? J From total world energy consumption to average consumption per capita • Energy consumption 16 TW in 2005 ‐> per capita consumption in kW? • Daily per capita consumption in MJ? • Result: the average person uses the energy equivalent of over 5 liters of oil Quantities of Energy Units based on oil Units based on c oal other units History • Publication of national and international energy data ‐> development of the 2nd half of the 20th century • But records of dealings in commodities are as old as trade itself • Dominant energy source ‐> units, ex. Britain: – Into the eighties: tonnes of coal equivalent – Since seventies: tonnes of oil equivalent Tonnes, tons, and short tons • 1 tonne (or metric tonne) = 1000 kg = 2205 lb • 1 ton = 1016 kg = 2240 lb • 1 short ton = 907 kg = 2000 lb • 1 lb = ? kg Units Based on Oil • 1 tonne of oil equivalent (1 toe) is the heat energy released in the complete combustion of 1000 kg of oil • Varies between crude oil from different regions, but a commonly used world average is: 1 toe ≈ 41.88 GJ ≈ 42 GJ ( I have also seen 45 GJ) • 1 barrel comes from the size of the barrels used to carry oil from the world’s first drilled well in Pennsylvania (1860s): – 1 barrel (bbl) = 42 US gal = 35 imperial gal ≈ 160 l – How is a barrel of oil related to a tonne of oil? volume ‐> mass, different densities of crude oil from different regions again world average: 1 tonne ≈ 7.33 bbl - 1 barrel of oil equivalent (1 boe) ≈ 5.71 GJ - Oil industry ‐> million barrels daily (Mbd) (exercise world energy use) Units Based on Oil (2) Energy dentsity Energy content per content per tonne liter petrol 44 GJ lower 33 MJ Crude oil 42 GJ higher 36 MJ Units Based on Coal • 1 tonne of coal equivalent (1 tce) is the heat energy released in burning of 1000 kg of coal • Coal is much more variable than crude oil: energy per tonne ranges from less than 20 GJ to over 30 GJ • Often adopted: 1 tce ≈ 28 GJ The BTU and Related Units The BTU and Related Units • The British Thermal Unit: 1 BTU is the heat energy needed to warm 1 pound of water by 1 degree Fahrenheit: 1 BTU = 1055 J ≈ 1 kJ • Multiples : therm = 105 BTU quad = quadrillion BTU = 1015 BTU = 1.055 EJ The Calorie and Related Units • The Calorie: 1 Calorie is the heat energy needed to warm 1 g of water by 1 degree Celsius: 1 cal ≈ 4.2 J 252 cal ≈ 1 BTU 1 kcal ≈ 1 Cal • Food energy to support an adult 2000 Cal: (exercise) Because of the Laws of Probability • Probabilities and uncertainties in the microscopic world of atoms and molecules are the heart of the 2nd law! • Large number of microscopic elements + Random behavior Macroscopic average behavior No eccentricity in the Macro World ! Probability and Entropy • The 2nd Law for isolated, random systems with a large number of elements (like our Universe): – “Disorder is much more probable than order” – “ the direction of spontaneous change as a result of random influence is from order (low probability) to disorder (high probability)” • Entropy is the a quantitative measure of the extent of disorder in a system Likely and Unlikely .
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