Energy Principles http://www.nasa.gov AJ A.J. Both Dept. of Environmental Sciences Rutgers University
Preamble Energy can exist in different forms Energy can be transferred from one form to another Each energy transition has its own efficiency Energy transfer should only be evaluated within a system defined by boundaries The systems view has significantly expanded in recent years (global warming/climate change)
Converting energy to work or heat http://images.irondealer.com
Typical (overall) conversion efficiencies Incandescent lamp 5-10% High Pressure e Sodu Sodium lamp 25-30% Gasoline combustion engine 25-30% Diesel engine 35-40% Solar panel (PV) 10-20% Wind generator 20-35% Fuel cell 35-50% Coal fired power plant 25-35% Gas fired power plant 35-45% Nuclear power plant 30-35% Solar thermal collector 2-30% Natural gas fired heater 80-95%
Energy Quantities
Btu measurements and quantities Amount in Btu Thousand Btu (10 3 ) Typical measurement Space heater output (1/hr) Heat energy of a fuel (1/unit) Million Btu (10 6 ) Per capita energy consumption of some countries (1/yr) Billion Btu (10 9 ) Energy consumption of a US office park Trillion Btu (10 12 ) Energy consumption of all railroads (US or Europe) Quadrillion Btu (10 15 ) Energy consumption of an (Quads) entire country (1/yr)
SI measurements and quantities Prefix Symbol Factor Example micro μ 10-6 microns, visible wavelength milli m 10-3 ma, current flow from a single PV cell kilo k 10 3 kwh, home energy consumption Mega M 10 6 MW, output of a wind turbine Giga G 10 9 GW, output t of a power plant Tera T 10 12 TW, world s power plants Peta P 10 15 PJ, annual energy consumption by US railroads Exa E 10 18 EJ, annual energy consumption by an entire country
Energy Conversions http://www.celsias.com http://www.iftp-berlin.de http://www.ecoworld.com
Several useful conversion factors From: To: Multiply by Btu J 1,054.4 4 Btu cal 252 Btu/h W (J/s) 0.293 hp (mech) W 745.7 hp (boiler) Btu/h 33,445.7 ft m 0.3048 gal L 3.79 lb kg 0.454
Temperature conversions and scales ºC =(ºF 32) 5/9 ºF =9/5 ºC +32 K=ºC + 273.15 http://www.magnet.fsu.edu
Second Law of Thermodynamics: Heat flows from a hot to a cold object A given amount of heat can not be changed completely into energy to do work In other words: If you put a certain amount of energy into a system, you can not get all of it out as work. YOU CAN T BREAK EVEN!! (No perpetuum mobile, perpetual motion )
Heating values Lower heating value (LHV): amount of heat released during combustion without including the latent heat of vaporization Higher heating value (HHV): amount of heat released during combustion including the latent heat of condensation [MJ/kg] HHV LHV H 2 142.2 120.2 2 NG 52.2 47.1 propane 50.2 46.3 gasoline 46.5 43.4 diesel 45.8 42.8 coal 24.0 22.7 biomass 16-21 15-20 http://hydrogen.pnl.gov
Heating fuels Fuel Typical Conversion Efficiency (%)* Heat Value Electricity 95-100 3,413 Btu/kWh Natural gas** 80 1,000 Btu/ft 3 Propane 80 91,000 Btu/gal No. 2 fuel oil 75 140,000 Btu/gal No. 6 fuel oil (pre-heat) 75 150,000 Btu/gal Hard coal (anthracite) 65 13,000 Btu/lb Soft coal (bituminous) 65 12,000 Btu/lb Hard wood (dry)*** 65 7,000 Btu/lb Wood chips 60 3,800 Btu/lb * Higher efficiencies are reported for some high-efficiency models Higher efficiencies are reported for some high-efficiency models ** 100 ft 3 of natural gas = 1 therm *** 20% moisture: oak ~ 26,000,000 Btu/cord (8 by 4 by 4 feet)
Energy content and pricing http://www.biomassrules.com Switchgrass $150.00 $/Ton $9.32
On-farm grown biofuels Crop Yield (gal of ethanol per acre; good soils) Energy ratio (Q in :Q out ) Sugar cane 700-850 1:8 Miscanthus 800-1,800* 1:6 Switchgrass 1,000-1150* 1:4 Soybean 50-70 (biodiesel) 1:3 Rape seed 100-140 (biodiesel) 1:3 Sugar beet 550-700 1:2 Corn 300-400 1:1.3 *Can be grown on marginal soils
Electrical Energy 12,000 V 240,000 V 8,000 V 240/120 V http://sol.sci.uop.edu
Electric circuits: useful equations V = I R (Ohm s Law) P = V I = I 2 R V = voltage [V] volt meter I = current [A] ammeter R = resistance [Ω] ohmmeter P = power [W] watt meter Energy = Power Time [J] http://www.dansdata.com Electric bill: kwh = (P/1000) T(with T in[hrs]) Electric bill: kwh = (P/1000) T (with T in [hrs]) (1 kwh = 3,600,000 Joules)
DC versus AC Direct current V, I + _ load one directional time Alternating current VI V, max two directional 360 ~ load 0 90 180 270 time one cycle
Alternating current: V i = V max sin(θ) V i = instantaneous voltage θ = phase angle Frequency: number of cycles per second unit: [Hz] (60 Hz in the US) Effective (apparent) voltage and current: V rms = V max / 2 I rms = I max / 2
Electric generator (AC) http://www.eng.cam.ac.uk ac http://upload.wikimedia.org
Mechanical Energy http://commons.wikimedia.org
2-stroke gasoline engine http://www.parsunoutboard.co.uk http://commons.wikimedia.org http://larrysmowershop.com
4-stroke gasoline engine Fuel injection 1. Intake 2. Compression 3. Expansion 4. Exhaust http://en.wikipedia.org
Diesel engine http://www.filmgreen411.com http://static.howstuffworks.com
Combined cycle power plant
Solar Energy Muehlhausen, Germany, 10 MW 19.3% efficient! http://www.solarfreaks.com
Impact of solar altitude on surface radiation Sun Sun 342 W/m 2 45º 342 W/m 2 cos(45º) = 0.707 242 W/m 2 1 m 2 1.41 m 2 242 W/m 2 = cos(45 ) 342 W/m 2
Solar altitude (α) by time of day For 40º N latitude (NJ EcoComplex) sinα = sin(l)sin(δ) + cos(l)cos(δ)cos(h) 90 L = latitude 80 δ = declination angle 70 60 h = hour angle 50 s) Sola ar altitude (degree (degrees) 90 80 70 60 50 40 30 20 10 0 20 For 5º N latitude Solar altitude ( 40 30 10 Winter solstice Equinox Summer solstice 0 1 2 3 4 5 6 7 8 9 101112131415161718192021222324 Time of the day (hr) Winter solstice Equinox Summer solstice 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time of the day (hr)
Cross section of PV cell Photograph courtesy Jack Rabin, NJAES http://www.esru.strath.ac.uk
http://www.unendlich-viel-energie.de
HAWT Wind Energy http://siteresources.worldbank.org
http://sosenergy.com
Classes of wind power density 10 m (33 ft) 50 m (164 ft) Class Density Upper speed Density Upper speed W/m 2 m/s (mph) W/m 2 m/s (mph) 1 0-100 4.4 (9.8) 0-200 5.6 (12.5) 2 100-150 5.1 (11.5) 200-300 6.4 (14.3) 3 150-200 5.6 (12.5) 300-400 7.0 (15.7) 4 200-250 6.0 (13.4) 400-500 7.5 (16.8) 5 250-300 6.4 (14.3) 500-600 8.0 (17.9) 6 300-400 7.0 (15.7) 600-800 8.8 (19.7) 7 400-1000 9.4 (21.1) 800-2000 11.9 (26.6) Source: http://www.eia.doe.gov
Wind speed and power u/u = α R (z/z R ) α = 1/7 u = wind speed z = height R = reference eee Typical reference heights: ht 10, 30, 50 m http://www.awea.org
Calculating wind turbine power E kin = ½ m v 2 [J]. Mass flow rate m = v A ρ [kg/s] Power = energy/time [W = J/s] Power = ½ ρ A v 3 C p N g N gb [W] C p = coefficient of performance 0.59 max (Betz limit) 0.35 for a good design N g = generator efficiency (50-80%) N gb = gearbox/bearing g efficiency ( 95%) Wind power density: P/A = ½ ρ v 3 [W/m 2 ]
NJ wind resources (30 m) Most viable wind generation sites: At the shore Off-shore Atlantic City http://farm3.static.flickr.com http://www.rowan.edu
Thank You!!! Questions?