Environmental Physics PHYS 1149
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This 39 page Class Notes was uploaded by Geo Mayer on Monday October 12, 2015. The Class Notes belongs to PHYS 1149 at Georgia Southern University taught by Anand Balaraman in Fall. Since its upload, it has received 39 views. For similar materials see /class/222053/phys-1149-georgia-southern-university in Physics 2 at Georgia Southern University.
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Date Created: 10/12/15
Chapter 10 Indirect from the Sun Water Wind and Biomass Solar Reflected flow sunlight 31 Infrared radiation 69 Tidal flow Tidal energy 00017 Energy of winds and currems Geothermal 0008 flow 0025 Photosynthesis 008 FIGURE 108 Energy Environment and Climate Copyright WiW Norton amp Company 2008 101 Indirect Solar Power Solar energy powers many of Earth s natural process 23 of solar energy goes into evaporating water 1 goes into increasing the internal energy of atmosphere 008 is captured by plantsphotosynthetic organisms So energy of flowing water moving air and Biomass are indirect forms of solar energy Hyd ropower Hydropower has a long history Greeks used it to derive mechanical energy Used to grind grains hammer iron saw wood weaving cloth Unrivaled source of mechanical energy before steam engine Also a main source of electrical energy in the past 40 in early 19005 33 in 19505 7 today Wind Biofuel 3 5 a i I Hydro Waste 47 FIGURE 1001 Energy Environment and Climate Copyright WW Norton amp Company 2006 Indirect Solar Energy Small pie graph at left shows that indirect solar energy supplies 8 percent of US net energy production Larger pie shows the contributions from different forms of indirect solar energy 101 Hydropower Source 23 of solar energy is 78 Wsqm Phase change of water 25 MJkg Nearly onefourth of the solar energy incident on Earth goes into evaporating water This is the source of the flowing water whose energy we capture with hyd ropower technologies FIGURE 1003 Energy Envilonmenl and Climate Cupyrighl ww Nanon a Company 2008 101 Hyd ropower Hydropower has a long history and today it sooe supplies some 17 A 500 percent of the world s 400 electrical energy mostly soo from dams built on rivers of H Africa North South Asia Europe America America FIGURE 1004 t and Climat Energy Environmen e Copyright WW Norton amp Company 2008 101 Hyd ropower Overshot Waterwheel Hydroelectric Dam Electric generator Stream Trough Reservoir Head Stream a FIGURE WG05 ergy Envilonment and Climate FIGURE WG06 Envilonment and Climate En Energy Copwighl wwv Norton amp Company 2000 Copwighl wwv Norton amp Company 2000 101 Hyd ropower aThe John Day Dam on the Columbia River in Oregon is a lowhead dam with a high flow rate b The Hoover Dam on the Colorado River at the ArizonaNevada border is a highhead dam with a lower flow rate FIGURE 10707 com Egrlrizizzmzszzm EaCh pFOdUCES just over 2 GW of hydroelectric power 101 Hydropower Hydropower represents energy ofthe highest quality and hydroelectric power generation produces essentially no pollution 0 In principle we can convert water s mechanical energy to electrical energy with 100 efficiency Why don t we have to worry about losses due to the second law of thermodynamics 101 Hydropower However hydropower dams alter river ecosystems and tropical installations may emit methane that contributes to climate change The construction of a hydroelectric dam floods terrestrial vegetation and when submerged vegetation decays and produces methane The hydroelectric resource is almost fully utilized especially in the developed world 102 Wind Power Wind is another indirect form of solar power Wind ranges from local breezes to air currents that encircle the globe History of wind power use Egyptians used sail boats in 3500 BCE Huge ships of 19th century used energy at a rate of 75 MW more than the largest wind turbines Land based windmills in China 4000 years ago 10000 windmills in England by 1750 Before rural electrification in 19305 wind mill pumped water in American fields Dutch wind mills are well known 102 Wind Fastest growing source of energy Roughly one percent of the incident solar energy goes into wind The power available from wind increases as the cube of the wind speed FIGURE wH Energy Environment and Climate Copyright WW Norton amp Company 2008 Wind Power Atmospheric Circulation Cells Hadlee Cell Equator 30 deg South moving surface winds Tropical Easterlies Mid Latitude Cell 30 60 deg North moving surface winds Westerlies Polar Cell 60 deg Pole South moving surface winds Polar Easterlies 102 Wind air motion FIGURE 1010 Energy Environment and Climate Copyright WW Norton amp Company 2008 102 Wind Class Wind power V nd speed WmZ ls meAwN l FIGURE 1012 Wind Power Annual average wind power map Wind power classes and average wind speed Wind variability and why average velocity is not a good measure of average wind power Accounting for this the US wind energy potential is several times the current energy requirement 06 of US land can give 20 of US energy requirement 12 of the world power through wind in 2020 102 Wind Modern wind turbines have electric power outputs of up to several megawatts and they re often grouped into wind farms with tens hundreds or thousands of turbines FiGURE 1013 102 Wind aSome of the four thousand wind turbines at California s San Gorgonio Pass b This much smaller installation in Sea rsburg Vermont is more controversial because of its ridgetop location Wind Power Not all the power locked in wind can be harnessed Albert Betz in 1919 derived an expression for the maximum extractable power 2a1aquot2 Rho vquot3 Betz Power Coefficient 59 Horizontal shafts 45 Vertical axes 30 Power coefficient also depends on ratio of the speed of blade tip to wind speed 102 Wind Total wind power 1 pv3 Maximum extractable power 59 of total Fraction of total wind power l O 02 04 06 08 1 Airspeed ratio a Power output MW 025 102 Wind Rated power Rated cm 393 3 speed Cutout spee speed i l l I l 0 5 10 15 20 25 30 35 Wind speed ms Energy Environmen an ima e Copyright wwv Norlon amp Company 200a High wind speeds could overpower a wind machine s electric generator or even damage the turbine blades There s also a minimum speed at which a turbine begins generating power 102 Wind Payback time is 2 3 months Wind s predominant environmental impact is aesthetic although wind turbines may also kill migrating birds and bats Ice throw problems They also pose a challenge for power distribution as the production from a wind turbine may increase or decrease dramatically within a number of hours 102 Wind Today wind is the fastest growing energy source and it provides a significant portion of the electrical energy in several European World wind capacity GW countries 20 10 Unlike direct solar 0 r o u D ED 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 alternatives Wind IS often economically competitive with conventional energy sources FIGURE 101 5 Energy Environment and Climate Copyrigm o ww Norion amp Company 200a 103 Biomass Most ancient form of energy source Domestication of fire between 16 MYA 078 MYA Wood was the main source of energy before coal took over in 1880 Photosynthesis stores energy at a rate of 133 TW which is 10 times the current energy consumption Nearly half of it comes from land plants They store energy at a rate of 051 Wsqm Energy stored in Earth s biomass is 15 10quot22 J which is 35 times the current annual energy requirements 103 Biomass Biomass contains solar energy captured by plants in the process of photosynthesis Earth s plants capture solar energy at about ten times the rate of human energy consumption Biomass may be burned directly for heat or electric power generation Decomposition of organic waste biomass releases combustible methane 103 Biomass Photosynthesis is a complex process that begins with a red chlorophyll absorbing solar energy Energy causes electron transfer that initiates a chain reaction Uses 466 10quot 18J of solar energy to combine 6 molecules of water and 6 molecules of C02 to make glucose 6HzO 6C02 E 9 C6H1206 602 103 Biomass 0 Different plant and bacterial species respond to different parts of spectrum For green plants energy absorption has two peaks One at 400 nm blue and the other one at 700 nm red So plants appear green Photosynthesis is not very efficient Spectral efficiency Inefficiency due to exothermic reactions involved in photosynthetic chain reaction 103 Biomass Primary Productivity Rate at which plants store solar energy Varies with plant type Insolation availability of water and minerals etc Gross Primary Productivity Primary productivity for the whole Earth Its value is estimated to be 133 TW Net Primary Productivity Half the energy produced by plants are consumed by the plants themselves for their functioning So Net Primary Productivity is half the Gross Primary Productivity 103 Biomass Using too much of planet s primary productivity endangers biosphere We need some of it to feed ourselves build shelter and cloth ourselves Energy stored in dry biomass is the same and is independent of origin Energy content Pure Glucose 16 MJkg Wood 20 MJkg Grass 1619 MJkg 103 Biomass Harnessing Biomass Simple way is to burn it Indoor air pollution is reduced by the invention of chimney in the 12th century Franklin stove invented in 1740 by Benjamin Franklin Efficient burning of wood requires chippingpelletting 200 wood powered electric plants operating in US generating 28 GW of energy 1 of US electricity comes from wood burning 103 Biomass Transportation accounts for M of the total energy consumption Only fossil fuels are useful in the transportation sector Alternatives to fossil fuels are bio fuels Biomass can be processed to give bio fuels Bio fuels are of two category Ethanol Biodiesel 103 Biomass Fermentation and chemical processing yield biofuels of which ethanol and biodiesel are most important Biomass and biofuels produce air pollutants although for some pollutants the amounts are lower than with fossil fuels 103 Biomass Bio Fuels 2 of US gasoline is bio fuel based 30 of Brazilian gasoline is bio fuel based 0 Lacking in fossil fuels but endowed with abundant vegetation and warm climate Brazil opted for Bio fuels in 1975 Today it meets 30 of its fuel requirements through Bio fuels and exports excess production mainly to US and India BioFuel Ethanol Ethanol results in the fermentation of plant sugars Yeasts and other microbes do the fermentation to yield ethanol Ethanol is produced in USA with Corn which was found to have poor EROEI 11 2005 energy bill passed in US increases subsidies for Ethanol production hoping that the production will be doubled by 2012 Cellulose based Ethanol will have better EROEI Brazil uses Sugar cane which has better EROEI 410 India has significant potential BioFuel BioDiesel Biodiesel is most popular in Europe Biodiesel uses only the oil bearing seeds of a plant not the entire plant Biodiesel is mainly vegetable oil and fats InIUS Biodiesel is mainly Soybean oil and recycled cooking or Cooking oil is more viscous because ofthe presence of Glycerin Transesterification removes Glycerin and reduces the viscosity of biodiesel Biodiesel is often blended with petrol BS 320 3100 pure biodiesel 1 Most engines work up to 320 1 First diesel engine designed by Rudolph Diesel ran on groundnut oil World ethanol production billion liters 103 Biomass 30 25 Brazil United States and Canada European Union World 20 O 1975 AI 1 980 1 985 1 990 Year 1 995 2000 Energy Environment and Climate Copyright WW Norton amp Company 2008 103 Biomass Petrol l Diesel ULSD 2002 El BeeiEIOH l I Straw BOH l I Cereal EIOH 1 ll Rapeseed Biodiesel l I Wood HzlGaSlf39 l E Wood E10HHydrol 1 1 Wood MeOH oasm l I Wood FTAdiesel Gasif Waste Oil Biodiesel l 5 H2 Wind 13 O 20 40 50 8 0 160 12 0 kg C02 equiv per 6 fuel Depending on how it s grown and harvested biomass may be carbon neutral But unsustainable or energyintensive harvesting and processing mean that some biomass operations entail significant carbon emissions 103 Biomass Biomass generated as crops must compete with farmland that may normally be used to grow crops for food Switchgrass is emerging as an quotenergy crop that doesn t take up prime farmland