Renewable Power Systems

Wind & PV Basics

15 October 2007

Dr Peter Mark Jansson PP PE

Aims of Today’s Lecture

• Solar resources & basics

• PV materials & cell operation

• PV technology

• Wind resources

Solar declination

Period of cycle Date Solar Declination

Vernal equinox 21 March 0.0o

Summer solstice 21 June 23.4o

Autumnal equinox 21 September 0.0o

Winter solstice 21 December -23.4o

NOTE: Tropic of Cancer is 23.45o (N Latitude), Tropic of Capricorn is -23.45o (S Lat.)

Nice link – Solar Declination

• http://www.sciences.univ-nantes.fr/physique/perso/gtulloue/Sun/motion/Declination_a.html

Declination responsible for day-length

• North of latitude 66.55o (the Arctic circle) the earth experiences continuous light at the summer solstice

• South of latitude -66.55o (the Antarctic circle) the earth experiences continuous darkness at the summer solstice

• North of latitude 66.55o (the Arctic circle) the earth experiences continuous darkness at the winter solstice

• South of latitude -66.55o (the Antarctic circle) the earth experiences continuous light at the winter solstice

Rule of Thumb

• Maximum annual solar collector performance (weather independent):• Achieved when collector is facing equator, with a

tilt angle equal to latitude (north or south latitude)• Why?

• In this geometry (the collector facing the equator with this tilt angle) the solar radiation it receives will be normal to its surface at the two equinoxes

Solar position in sky

• Sun’s location can be determined at any time in any place by determining or calculating its altitude angle (N) and its azimuth.

• Azimuth is the offset degrees from a true equatorial direction (south in northern hemisphere), positive in morning (E of S) and negative after solar noon (W of S).

Azimuth-s and Altitude-N

Technology Aid

• Sun Path Diagrams• Solar PathFinderTM

• SunChart

• Allows location of obstructions in the solar view and enables estimation of how much reduction in annual solar gain that such shading provides

Sun Path diagram

Maximize your Solar Window

Magnetic declination

• When determining true south with a magnetic compass it is important to know that magnetic south and true (geometric) south are not the same in North America, (or anywhere else).

• In our area, magnetic south is +/- 12o west of true south

Source: http://www.ngdc.noaa.gov/seg/geomag/jsp/struts/calcDeclination

Orientation and Incoming Energy

Flux changes based on module orientation

• Fixed Panel facing south at 40o N latitude• 40o tilt angle: 2410 kWh/m2

• 20o tilt angle: 2352 kWh/m2 (2.4% loss)• 60o tilt angle: 2208 kWh/m2 (8.4% loss)

• Fixed panel facing SE or SW (azimuth)• 40o tilt angle: 2216 kWh/m2 (8.0% loss)• 20o tilt angle: 2231 kWh/m2 (7.4% loss)• 60o tilt angle: 1997 kWh/m2 (17.1% loss)

Benefits of tracking

• Single axis –• 3,167 kWh/m2

• 31.4% improvement over fixed at 40o N latitude

• Two axis tracking –• 3,305 kWh/m2

• 37.1% improvement over fixed at 40o N latitude

Total Solar Flux

• Direct Beam• Radiation that passes in a straight line through the

atmosphere to the solar receiver (required by solar concentrator systems) 5.2 vs. 7.2 (72%) in Boulder CO

• Diffuse• Radiation that has been scattered by molecules and

aerosols in the atmosphere

• Reflected• Radiation bouncing off ground or other surfaces

Solar Resources - Direct Beam

Solar Resources – Total & Diffuse

Annual Solar Flux variation

• 30 – years of data from Boulder CO

• 30-year Average: 5.5 kWh/m2 /day

• Minimum Year: 5.0 kWh/m2 /day• 9.1% reduction

• Maximum Year: 5.8 kWh/m2 /day• 5.5% increase

Benefits of Real vs. Theoretical Data

• Real data incorporates realistic climatic variance• Rain, cloud cover, etc.

• Theoretical models require more assumptions• In U.S. – 239 sites have collected data, 56 have

long term solar measurements (NREL/NSRDB)• Globally – hundreds of sites throughout the world

with everything from solar to cloud cover data from which good solar estimates can be derived (WMO/WRDC)

Solar Flux Measurement devices

• Pyranometer• Thermopile type (sensitive to all radiation)• Li-Cor silicon-cell (cutoff at 1100m)• Shade ring (estimates direct-beam vs. diffuse)

• Pyrheliometer• Only measures direct bean radiation

PV History

• 1839: Edmund Becquerel, 19 year old French physicist discovers photovoltaic effect

• 1876: Adams and Day first to study PV effect in solids (selenium, 1-2% efficient)

• 1904: Albert Einstein published a theoretical explanation of photovoltaic effect which led to a Nobel Prize in 1923

• 1958: first commercial application of PV on Vanguard satellite in the space race with Russia

Historic PV price/cost decline

• 1958: ~$1,000 / Watt

• 1970s: ~$100 / Watt

• 1980s: ~$10 / Watt

• 1990s: ~$3-6 / Watt

• 2000-2007: • ~$1.8-2.5/ Watt (cost)• ~$3.50-4.75/ Watt (price)

PV cost projection

• $1.50 $1.00 / Watt

• 2006 2008

• SOURCE: US DOE / Industry Partners

PV Module Prices

Source: P. Maycock, The World Photovoltaic Market 1975-1998 (Warrenton, VA: PV Energy Systems, Inc., August 1999), p. A-3.

PV technology efficiencies

• 1970s/1980s 2003 (best lab efficiencies)

• 3 13% amorphous silicon

• 6 18% Cu In Di-Selenide

• 14 20% multi-crystalline Si

• 15 24% single crystal Si

• 16 37% multi-junction concentrators

PV Module Performance

• Temperature dependence• Nominal operating cell temperature (NOCT)

SNOCT

TT ambcell

8.0

20

Tc = cell temp, Ta = ambient temp (oC), S = insolation kW/m2

PV Output deterioration

• Voc drops 0.37%/oC

• Isc increases by 0.05%/oC

• Max Power drops by 0.5%/oC

PV Module Shipments

Wind & PV Markets (’94 -’06)Market for Wind & PV

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Year

Me

ga

Wa

tts

Wind production

PV production

Wind Market

Annual Installed Wind Capacity

02000400060008000

10000120001400016000

Year

Meg

aWat

ts

PV Market

PV Module Shipments

0

500

1000

1500

2000

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Year

Meg

aWat

ts

Amorphous Si

Amorphous Si

Cadmium Telluride

Multi-crystalline Si

Multi-crystalline Si

Single Crystal Si

Semi-Conductor Physics

• PV technology uses semi-conductor materials to convert photon energy to electron energy

• Many PV devices employ • Silicon (doped with Boron for p-type material

or Phosphorus to make an n-type material)• Gallium (31) and Arsenide (33)• Cadmium (48) and Tellurium (52)

p-n junction

• When junction first forms as the p and n type materials are brought together mobile electrons drift by diffusion across it and fill holes creating negative charge, and in turn leave an immobile positive charge behind. The region of interface becomes the depletion region which is characterized by a strong E-field that builds up and makes it difficult for more electrons to migrate across the p-n junction.

Depletion region

• Typically 1 m across• Typically 1 V• E-field strength > 10,000 V/cm

• Common, conventional p-n junction diode• This region is the “engine” of the PV Cell

• Source of the E-field and the electron-hole gatekeeper

Band–gap energy

• That energy which an electron must acquire in order to free itself from the electrostatic binding force that ties it to its own nucleus so it is free to move into the conduction band and be acted on by the PV cell’s induced E-field structure.

Band Gap (eV) and cutoff Wavelength

• PV Materials Band GapWavelength

• Silicon 1.12 eV 1.11 m

• Ga-As 1.42 eV 0.87 m• Cd-Te 1.5 eV 0.83 m• In-P 1.35 eV 0.92 m

Photons have more than enough or not enough energy

• Sources of PV cell losses (=15-24%):• Silicon based PV technology max()=49.6%

• Photons with long wavelengths but not enough energy to excite electrons across band-gap (20.2% of incoming light)

• Photons with shorter wavelengths and plenty (excess) of energy to excite an electron (30.2% is wasted because of excess)

• Electron-hole recombination within cell (15-26%)

p-n junction

• As long as PV cells are exposed to photons with energies exceeding the band gap energy hole-electron pairs will be created

• Probability is still high they will recombine before the “built-in” electric field of the p-n junction is able to sweep electrons in one direction and holes in the other

Generic PV cellIncoming Photons

E-Field

Electrons

Holes

+ + + Accumulated Positive Charges + + +

- - - - Accumulated Negative Charges - - - -

Depletion Region

Bottom Electrical Contact

Top Electrical Contacts

+ + + + + + + + + - - - - - - - - -

I

electrons

p-type

n-type

PV Module Performance

• Standard Test Conditions

• 1 sun – 1000 watts/m2 = 1kW/m2

• 25 oC Cell Temp

• AM 1.5 (Air Mass Ratio)

• I-V curves

• Key Statistics: VOC, ISC, Rated Power, V and I at Max Power

PV specifications (I-V curves)

• I-V curves look very much like diode curve

• With positive offset for a current source when in the presence of light

From cells to modules

• Primary unit in a PV system is the module

• Nominal series and parallel strings of PV cells to create a hermetically sealed, and durable module assembly

• DC (typical 12V, 24V, 48V arrangements)

• AC modules are available

From Cells to Arrays

PV Module Performance

• Temperature dependence• Nominal operating cell temperature (NOCT)

SNOCT

TT ambcell

8.0

20

Tc = cell temp, Ta = ambient temp (oC), S = insolation kW/m2

PV Output deterioration

• Voc drops 0.37%/oC

• Isc increases by 0.05%/oC

• Max Power drops by 0.5%/oC

BP 3160

• Rated Power : 160 W

• Nominal Voltage: 24V

• V at Pmax = 35.1

• I at Pmax = 4.55

• Min Warranty: 152 W

• NOTE: I-V Curves

Remember

• PV modules stack like batteries• In series Voltage adds,

• constant current through each module

• In parallel Current adds, • voltage of series strings must be constant

• Build Series strings first, then see how many strings you can connect to inverter

Wiring the System

PV system types

• Grid Interactive – and BIPV• Stand Alone

• Pumping

• Cathodic Protection

• Battery Back-Up Stand Alone• Medical / Refrigeration

• Communications

• Rural Electrification

• Lighting

Grid Interactive

Grid-interactive roof mounted

Building Integrated PV

Stand-Alone – First House

Remote

PV – Grid Active Rebates

• 2007 NJCEP Rebates• PV Systems < 10 kW $3.50 - $4.10/watt• Maximum incentive (60% of system costs)• Systems > 10kW

• > 10 to 40 kW $2.50 - $3.15/watt• > 40 to 100 kW $2.25 - $2.50/watt• > 100 to 500 kW $2.00 - $2.30/watt• > 500 up to 700 kW $1.75 - $1.85/watt

NJ Wind Resources

Wind Turbines

Wind Turbines

• A wind turbine obtains its power input by converting the force of the wind into a torque acting on the rotor blades.

• The amount of energy which the wind transfers to the rotor depends on the density of the air, the rotor area, and the wind speed.

Wind Turbines

• A wind turbine will deflect the wind before it even reaches the rotor plane which means that all of the energy in the wind cannot be captured using a wind turbine.

Wind Power and Wind Speed (v)

• Power/Energy is proportional to v3

• Why?

Wind Turbine Energy

The annual energy delivered by a wind turbine can be estimated by using the equation:

1000W

1kwh/yr m) length (Rotor

4)(W/m power windAverageEnergy 22 87603.0

The cost of electricity will vary with wind speed. The higher the average wind speed, the greater the amount of energy, and the lower the cost of electricity

Wind Power ClassificationsWind Power Class

Average Speed m/s

Average Speed mph

10-m Power Density W/m2

50-m Power Density W/m2

1 0-4.4 0-9.8 0-100 0-200

2 4.4-5.1 9.8-11.4 100-150 200-300

3 5.1-5.6 11.4-12.5 150-200 300-400

4 5.6-6.0 12.5-13.4 200-250 400-500

5 6.0-6.4 13.4-14.3 250-300 500-600

6 6.4-7.0 14.3-15.7 300-400 600-800

7 7.0-9.5 15.7-21.5 400-1000 800-2000

Delaware Bay / Coastal Wind Speeds

•Areas along shore or in mountains may be ideal for wind power•Wind speeds as low as:4.5 -5.5 m/s for res farms/comm >6.0 m/s can be used for power farmsAt 6.5 m/s, electricity can be below

• $0.07/kWhTrue Wind Solutions

2007 NJCEP Rebates

• Wind and Sustainable Biomass Systems• Systems < 10 kW $5.00/watt• Maximum incentive (60% of system costs)• Systems > 10kW • First 10 kW $3.00/watt• > 10 to 100 kW $2.00/watt• > 100 to 500 kW $1.50/watt• > 500 kW, up to 1000 kW $0.15/watt• Maximum incentive (30% of system costs)

10 kW Bergey Turbine in NJ

• Class 3 winds at ground – 5.5 m/s, 24 m (80ft) – 6.3 m/s aloft

• Power generated is ~18,000 kWh/year

• Turbine: $24,750

• Tower: $6,800

• Install/Misc: $5,500

• NJCEP Rebate (60%): $22,230

• Net Cost : $14,820

• 15 year electric cost: 5.5¢/kWh• Simple Payback: ~ 7.5 years

New Jersey Anemometer Loan Program

• USDOE, NJBPU/NJCEP, Rutgers and Rowan University have partnered to offer free wind energy analysis to farms seriously considering wind

• 1 – year onsite wind measurement• Tower and anemometer installed at no

charge• Contacts: • NJCEP: Alma Rivera 1.973-648-7405 or email:

alma.rivera@bpu.state.nj.us• Rowan: Dr. Peter Mark Jansson 1.856.256.5373 or email:

jansson@rowan.edu• Rutgers: Dr. Michael R. Muller 1.732.445.3655 or email:

muller@caes.rutgers.edu

New Jersey Anemometer Loan Program

• Regional Data from the South Available OnLine

• http://www.rowan.edu/cleanenergy

New Jersey Wind Power - ACUA