Renewable Power Systems
Wind & PV Basics
15 October 2007
Dr Peter Mark Jansson PP PE
Aims of Today’s Lecture
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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.univnantes.fr/physique/perso/gtulloue/Sun/motio
n/Declination_a.html
Declination responsible for daylength
• 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 1100m)
• 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
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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
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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)
Tcell
 NOCT  20 
 Tamb  
S
0.8


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+05
Wind production
PV production
MegaWatts
1.00E+04
1.00E+03
1.00E+02
1.00E+01
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Year
Wind Market
16000
14000
12000
10000
8000
6000
4000
2000
0
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
MegaWatts
Annual Installed Wind Capacity
Year
PV Market
PV Module Shipments
MegaWatts
2000
1500
1000
500
0
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
Year
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
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PV Materials
Silicon
Ga-As
Cd-Te
In-P
Band Gap
1.12 eV
1.42 eV
1.5 eV
1.35 eV
Wavelength
1.11 m
0.87 m
0.83 m
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
cell
Incoming Photons
Top Electrical Contacts
electrons 
- - - - Accumulated Negative Charges - - - -
n-type
Holes
E-Field
+
-
p-type
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
Depletion
Region
Electrons
+ + + Accumulated Positive Charges + + +
Bottom Electrical Contact
I 
PV Module Performance
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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)
Tcell
 NOCT  20 
 Tamb  
S
0.8


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
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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
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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
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> 10 to 40 kW
> 40 to 100 kW
> 100 to 500 kW
> 500 up to 700 kW
$2.50 - $3.15/watt
$2.25 - $2.50/watt
$2.00 - $2.30/watt
$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:

1kw
Energy  0.3  Average wind power (W/m 2 )  (Rotor length m)2  8760 h/yr 
4
1000W
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 Classifications
Wind Power Average
Class
Speed m/s
Average
Speed mph
10-m Power 50-m Power
Density W/m2 Density W/m2
1
2
3
4
5
6
7
0-9.8
0-100
0-200
9.8-11.4
100-150
200-300
11.4-12.5
150-200
300-400
12.5-13.4
200-250
400-500
13.4-14.3
250-300
500-600
14.3-15.7
300-400
600-800
15.7-21.5
400-1000
800-2000
0-4.4
4.4-5.1
5.1-5.6
5.6-6.0
6.0-6.4
6.4-7.0
7.0-9.5
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 farms
At 6.5 m/s, electricity
can be below
• $0.07/kWh
True Wind Solutions
2007 NJCEP Rebates
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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
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Turbine: $24,750
Tower: $6,800
Install/Misc: $5,500
NJCEP Rebate (60%): $22,230
Net Cost : $14,820
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15 year electric cost: 5.5¢/kWh
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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
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New Jersey Anemometer Loan Program
• Regional Data from the South Available OnLine
• http://www.rowan.edu/cleanenergy
New Jersey Wind Power - ACUA