Energy Principleshttp://www.nasa.gov

A J BothA.J. BothDept. of Environmental SciencesRutgers University

• Preamble

Energy can exist in different forms

E b t f d f f t thEnergy can be transferred from one form to another

Each energy transition has its own efficiencyEach energy transition has its own efficiency

Energy transfer should only be evaluated within a gy ysystem defined by boundaries

Th i h i ifi l d d iThe 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 Sodium lamp 25-30%g essu e Sod u a p 5 30%Gasoline combustion engine 25-30%Diesel engine 35-40%gSolar panel (PV) 10-20%Wind generator 20-35%Fuel cell 35-50%Coal fired power plant 25-35%G fi d l t 35 45%Gas fired power plant 35-45%Nuclear power plant 30-35%Solar thermal collector 2 30%Solar thermal collector 2-30%Natural gas fired heater 80-95%

Energy Quantities

• Btu measurements and quantities

Amount in Btu Typical measurementThousand Btu (103) Space heater output (1/hr)Thousand Btu (10 ) Space heater output (1/hr)

Heat energy of a fuel (1/unit)Million Btu (106) Per capita energyMillion Btu (10 ) Per capita energy

consumption of some countries (1/yr)

Billion Btu (109) Energy consumption of a US office park

Trillion Btu (1012) Energy consumption of all railroads (US or Europe)

Q d illi Bt (1015) E ti fQuadrillion Btu (1015) (Quads)

Energy consumption of an entire country (1/yr)

• SI measurements and quantitiesP fi S b l F t E lPrefix Symbol Factor Examplemicro μ 10-6 microns, visible wavelength

3milli m 10-3 mA, current flow from a single PV cell

kilo k 103 kWh home energy consumptionkilo k 103 kWh, home energy consumptionMega M 106 MW, output of a wind turbineGi G 109 GW t t f l tGiga G 109 GW, output of a power plantTera T 1012 TW, world’s power plantsP t P 1015 PJ l tiPeta P 1015 PJ, annual energy consumption

by US railroadsExa E 1018 EJ annual energy consumptionExa E 1018 EJ, annual energy consumption

by an entire country

Energy Conversions

http://www.iftp-berlin.dehttp://www.celsias.com http://www.ecoworld.com

• Several useful conversion factors

From: To: Multiply byBtu J 1 054 4Btu J 1,054.4Btu cal 252Btu/h W (J/s) 0.293hp (mech) W 745.7hp (boiler) Btu/h 33,445.7ft m 0 3048ft m 0.3048gal L 3.79lb kg 0.454

• Temperatureconversionsconversions and scales

ºC = (ºF – 32)·5/9C = ( F – 32) 5/9

ºF = 9/5·ºC + 32F = 9/5 C + 32

K = ºC + 273 15K = C + 273.15

http://www.magnet.fsu.edu

• Second Law of Thermodynamics:

Heat flows from a hot to a cold objectA given amount of heat can not beA given amount of heat can not bechanged completely into energy to do work

In other words: If you put a certain amount of energy into a system you can not get allof energy into a system, you can not get allof it out as work.

YOU CAN’T BREAK EVEN!!(No perpetuum mobile perpetual motion )(No perpetuum mobile, perpetual motion…)

• Heating values

Lower heating value (LHV): amount of heat released

[MJ/kg] HHV LHV

H2 142.2 120.2during combustion without including the latent heat of vaporization

2

NG 52.2 47.1of vaporization

Higher heating value (HHV):

propane 50.2 46.3

gasoline 46.5 43.4Higher heating value (HHV): amount of heat releasedduring combustion including

g

diesel 45.8 42.8

the latent heat ofcondensation

coal 24.0 22.7

biomass 16-21 15-20http://hydrogen.pnl.gov

TypicalConversion

• Heating fuels

Fuel Efficiency (%)* Heat ValueElectricity 95-100 3 413 Btu/kWhElectricity 95 100 3,413 Btu/kWhNatural gas** 80 1,000 Btu/ft3Propane 80 91,000 Btu/galNo. 2 fuel oil 75 140,000 Btu/galNo. 6 fuel oil (pre-heat) 75 150,000 Btu/galH d l ( th it ) 65 13 000 Bt /lbHard coal (anthracite) 65 13,000 Btu/lbSoft coal (bituminous) 65 12,000 Btu/lbHard wood (dry)*** 65 7 000 Btu/lbHard wood (dry) 65 7,000 Btu/lbWood 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 ft3 of natural gas = 1 therm*** 20% moisture: oak ~ 26,000,000 Btu/cord (8 by 4 by 4 feet)

http://www.biomassrules.com• Energy content and pricing

Switchgrass $150.00 $/Ton $9.32

• On-farm grown biofuels

Crop Yield (gal of ethanol per acre; good soils)

Energy ratio (Qin:Qout)

Sugar cane 700-850 1:8Miscanthus 800-1,800* 1:6,Switchgrass 1,000-1150* 1:4Soybean 50 70 (biodiesel) 1:3Soybean 50-70 (biodiesel) 1:3

Rape seed 100-140 (biodiesel) 1:3

Sugar beet 550-700 1:2

Corn 300-400 1:1.3Corn 300 400 1:1.3

*Can be grown on marginal soils

Electrical EnergyElectrical Energy

240/120 V8,000 V240,000 V12,000 V

http://sol.sci.uop.edu

• Electric circuits: useful equations

V = I · R (Ohm’s Law)P = V · I = I2 · R

V = voltage [V] volt meterI = current [A] ammeterI = current [A] ammeterR = resistance [Ω] ohmmeterP = power [W] watt meterP = power [W] watt meter

Energy = Power · Time [J] http://www.dansdata.comEnergy = Power Time [J]

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

one directional

loadtime

one directional+_

Alternating

time

V IAlternatingcurrent

V, Imax

360°

two directional

load~time0 90° 180° 270°

360

one cycle

• Alternating current:

Vi = Vmax · sin(θ)Vi = instantaneous voltageθ = phase angle

Frequency: number of cycles per secondunit: [Hz] (60 Hz in the US)

Effective (apparent) voltage and current:Vrms = Vmax/√2 Irms = Imax/√2

• Electric generator (AC)

http://www eng cam ac ukhttp://upload.wikimedia.org

http://www.eng.cam.ac.uk

Mechanical Energy

http://commons.wikimedia.org

• 2-stroke gasoline enginehttp://www.parsunoutboard.co.uk

http://larrysmowershop.comhttp://commons.wikimedia.org

• 4-stroke gasoline engine

Fuel injectionFuel injection

1 Intake1. Intake2. Compression3 Expansion3. Expansion4. Exhaust

http://en.wikipedia.org

• Diesel engine

http://www.filmgreen411.comp g

http://static.howstuffworks.com

• Combined cyclepower plantpower plant

Solar EnergyMuehlhausen, Germany, 10 MW

http://www.solarfreaks.com19.3% efficient!

• Impact of solar altitude on surface radiation

Sun Sun

342 W/m2342 W/m2

45º

342 W/m2 242 W/m2cos(45º) = 0.707

1 m2 1.41 m2

242 W/m2 = cos(45°)·342 W/m2

• Solar altitude (α)by time of day 70

80

90

s)

Winter solsticeEquinoxSummer solsticeby time of day

For 40º N latit de 30

40

50

60

ar a

ltitu

de (d

egre

e

For 40º N latitude(NJ EcoComplex)

0

10

20

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

Sola

sinα = sin(L)sin(δ) + cos(L)cos(δ)cos(h)L = latitude

Time of the day (hr)

90L latitudeδ = declination angleh = hour angle

50

60

70

80

(deg

rees

)

Winter solsticeEquinoxSummer solstice

For 5º N latitude

g

20

30

40

50

Sola

r alti

tude

(

For 5 N latitude0

10

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Time 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

Wind Energy

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 speedClass Density

W/m2

Upper speedm/s (mph)

DensityW/m2

Upper speedm/s (mph)

1 0-100 4.4 (9.8) 0-200 5.6 (12.5)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)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)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

7 400 1000 9.4 (21.1) 800 2000 11.9 (26.6)

• Wind speedand power

u/uR = (z/zR)α

and power

u/uR (z/zR)α = 1/7u = wind speedu wind speedz = heightR = referencee e e ce

Typical referenceh i htheights: 10, 30, 50 m

http://www.awea.org

• Calculating wind turbine power

E ½ 2 [J]Ekin = ½ m v2 [J]

Mass flow rate m = v A ρ [kg/s].

ρ [ g ]

Power = energy/time [W = J/s]

Power = ½ ρ A v3 Cp Ng Ngb [W]Cp = coefficient of performancep p

0.59 max (Betz limit)0.35 for a good designg g

Ng = generator efficiency (50-80%)Ngb = gearbox/bearing efficiency (≤ 95%)gb g g y ( )

Wind power density: P/A = ½ ρ v3 [W/m2]

• NJ wind resources (30 m)

Most viable wind generation sites:

At the shoreOff-shore

Atlantic City

http://www.rowan.edu

http://farm3.static.flickr.com

Thank You!!!Questions?