Advanced Power Systems

1
Advanced Power Systems

• ECE 09.402.02 and ECE 09.504.02
• Lecture 9 Solar and PV Basics
• 26 March 2007
• Dr Peter Mark Jansson PP PE

2
admin announcements

• Four weeks until Final Project Reports due
• Mid-Term returned today
• HWs and LMs up front
• Project Feedback up front

3
See revised class schedule

• Final Presentation Dates
• 23 and 30 April, 7 May 2007
• You May Be Called for ANY WEEK
• One Date reserved for PV system tour

4
Mid Term Exam Grades

• Average 72
• Min 56
• Max 89
• HWs still outstanding, late is better than 0

5
New homework

• HW 8 due next Monday 2 Apr
• To be posted on web
• Renewable Efficient Electric Power Systems
  pp. 439- 443
• 7.1, 7.2, 7.3, 7.4, 7.5, 7.6, 7.8, 7.17
• Renewable Efficient Electric Power Systems
  pp. 502- 504
• 8.1, 8.5, 8.6, 8.7

6
Aims of Todays Lecture

• Part One complete summary of ch. 7 concepts
• Solar Rsources
• Overview of Chapter 8 PV Cells/Modules
• Short break at 600 p.m.
• Part Two
• Complete Chapter 8 PV Cells/Modules

7
Key Concepts from Chapter 7

• The Solar Spectrum
• Our Star the Sun
• 1.4 million km diameter
• 3.8 x 1020 MW of electromagnetic energy
• Blackbody radiation depends on temperature
• The Sun 5800 oK
• The Earth 288 oK

8
Plancks and Stefan-Boltzmann Laws
9
Wiens Displacement Rule
?max wavelength at which the spectrum reaches
its maximum point
10
What is peak wavelength of Sun?
11
What is peak wavelength of Earth?
12
Earth receives Sunlight reflects Earthlight

• The Earths atmosphere reacts very differently
  to the much longer wavelengths emitted by the
  Earths surface compared with the relatively
  shorter wavelengths arriving from the Sun. This
  difference is the fundamental factor responsible
  for the greenhouse effect Masters, p. 387

13
LM 1

• What are peak radiation wavelengths from the
  Moons dark side (assume -35o C) and from its
  bright side (assume 45o C)?

14
Solar declination
where n 1(Jan1), 32 (Feb1), 60(Mar1),etc.
Source The American Ephemeris and Nautical
Almanac
15
Solar declination
NOTE Tropic of Cancer is 23.45o (N Latitude),
Tropic of Capricorn is -23.45o (S Lat.)
16
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

17
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

18
Maximum Performance on Any Day

• Maximum solar performance
• Achieved when collector is facing equator, with a
  tilt angle equal to 90o - ?N
• What is ?N ? Altitude angle angle between the
  sun and the local horizon directly beneath the
  sun at solar noon

19
LM 2

• Today is 26 March (n85), if we wanted to
  optimize our collection of solar radiation today
  what tilt angle would we have used on our modules
  here in Glassboro?
• Assume latitude 39.7o

20
Solar position in sky

• Suns 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).

21
Solar Hour angle (H)

• Solar Hour angle (H) is the number of degrees the
  earth must rotate before the sun will be directly
  above your local meridian (due true south for
  most of us).

22
Solar position in sky
where ?altitude, ?S azimuth, Llatitude, ?
declination, Hhour angle
Note In spring summer in early morning and
late afternoon azimuth may be greater than 90o,
so must be tested
23
Solar position in sky
Note In spring summer, in the early morning
and in the late afternoon azimuth may be greater
than 90o, so azimuth angle ?s must be tested
where Llatitude, ?declination, Hhour angle
24
Azimuth-?s and Altitude-?N
25
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
• We will visit this again in PV system design

26
Sun Path diagram
27
Maximize your Solar Window
28
LM 3

• Find the altitude angle and azimuth angle for the
  sun at 300pm solar time in Boulder CO (latitude
  40o) on the day of the summer solstice
• L 40, H -45, ? 23.45

29
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

30
Source http//www.ngdc.noaa.gov/seg/geomag/jsp/st
ruts/calcDeclination
31
Total Solar Flux (units)

• kWh/m2
• Most common
• 316.95 Btu/ft2
• 85.98 langleys
• langley
• 1 cal/cm2
• 41.856 kjoules/m2
• 0.01163 kWh/m2
• 3.6878 Btu/ft

32
Orientation and Incoming Energy
33
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)

34
Benefits of tracking

• Single axis
• 3,167 kWh/m2
• 31.4 improvement at 40o N latitude
• Two axis tracking
• 3,305 kWh/m2
• 37.1 improvement at 40o N latitude

35
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

36
Solar Resources - Direct Beam
37
Solar Resources Total Diffuse
38
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

39
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)

40
LM 4

• Using Table 7.8 on page 426, determine the June
  monthly production of a 20 efficient PV system
  with only 25 loss of sun due to cloudy weather
  under the following conditions
• 20 m2 w/ single axis tracker
• 20 m2 south facing at 20o tilt angle
• 20 m2 laying flat on a horizontal roof

41
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

42
Key Concepts of Chapter 8

• Photovoltaic history
• PV technologies materials
• Semiconductor physics
• Generic PV cell IV Curves
• From Cells ? Modules ? Arrays
• Series and Parallel configurations

43
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
  

44
Historic PV price/cost decline

• 1958 1,000 / Watt
• 1970s 100 / Watt
• 1980s 10 / Watt
• 1990s 3-6 / Watt
• 2000-2004
• 1.8-2.5/ Watt (cost)
• 3.50-4.75/ Watt (price)

45
PV cost projection

• 1.50 ? 1.00 / Watt
• 2005 ? 2008
• SOURCE US DOE / Industry Partners

46
PV Module Prices
Source P. Maycock, The World Photovoltaic Market
1975-1998 (Warrenton, VA PV Energy Systems,
Inc., August 1999), p. A-3.
47
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

48
PV Module Performance

• Temperature dependence
• Nominal operating cell temperature (NOCT)

Tc cell temp, Ta ambient temp (oC), S
insolation kW/m2
49
PV Output deterioration

• Voc drops 0.37/oC
• Isc increases by 0.05/oC
• Max Power drops by 0.5/oC

50
LM 5

• Estimate Cell temperature, open circuit voltage,
  and maximum power output for a 150-watt BP2150S
  module (see Table 8.3, p. 475) under conditions
  of 1 sun (1 kW/m2) and ambient temperature of 30
  oC, NOCT for module is 47 oC
• At 25 C Voc 42.8

51
PV Module Shipments
52
Wind PV Markets (94 -06)
Wind production PV production
53
Wind Market
54
PV Market
55
LM 6

• How does the cost of PV technology (price) in
  1970, compare with todays PV module prices in
  /Watt? Write your answer as a price in each
  period and a percentage reduction that occurred
  during those three decades.

56
Amorphous Si
57
Amorphous Si
58
Cadmium Telluride
59
Multi-crystalline Si
60
Multi-crystalline Si
61
Single Crystal Si
62
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)

63
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.

64
Depletion region

• Typically 1 ?m across
• Typically 1 V
• E-field strength gt 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

65
Bandgap 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 cells induced E-field
  structure.

66
Band Gap (eV) and cutoff Wavelength

• PV Materials Band Gap Wavelength
• 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

67
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)

68
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

69
Generic PV cell
Incoming Photons
Top Electrical Contacts
electrons ?
- - - - Accumulated Negative Charges - - - -
n-type
Holes
E-Field
Depletion Region


- - - - - -
- - -
Electrons
p-type
Accumulated Positive Charges
Bottom Electrical Contact
I ?
70
LM 7

• What is maximum potential efficiency of a silicon
  based PV cell?
• What are the three major sources of the losses?

71
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

72
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

73
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

74
From Cells to Arrays
75
PV Module Performance

• Temperature dependence
• Nominal operating cell temperature (NOCT)

Tc cell temp, Ta ambient temp (oC), S
insolation kW/m2
76
PV Output deterioration

• Voc drops 0.37/oC
• Isc increases by 0.05/oC
• Max Power drops by 0.5/oC

77
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

78
LM 8

• Estimate Cell temperature, open circuit voltage,
  and maximum power output for a 150-watt BP2150S
  module (see Table 8.3, p. 475) under conditions
  of 1 sun (1 kW/m2) and ambient temperature of 30
  oC, NOCT for module is 47 oC
• At 25 C Voc 42.8

79
From modules to arrays

• Method
• First Determine Customer Needs (reduce)
• Determine Solar Resource (SP, model, calcs)
• Select PV Modules or
• Select DC-AC Inverter
• Look for Maximum Power Tracking Window
• Max DC voltage Current
• Assure Module Strings Voc and Isc meet inverter
  specifications

80
See Mesa Environmental Solar Audits

• Spreadsheet Customer Monthly Consumption
• Determine potential Shade Free Sites
• ID source for local Solar Resource Info
• Model (PVWATTS, PV FCHART, NJCEP)
• Weather Service Data
• Actual measurements from region

81
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

82
Match Modules With Inverter

• Find Optimal Fit of Series Strings
• TO BE IN MAX POWER TRACKING WINDOW
• Assure module s do not exceed Voc
• Find Optimal of Strings in Parallel
• TO MEET MODULE POWER RATING
• CURRENT TO BE LESS THAN MAX Isc
• Are Modules and Inverter a good match?
• Overall Hardware Utilization efficiency

83
Putting it all Together

• Customer Needs (energy usage ? reduce)
• PV System Design Requirements
• Solar Resource Assessment
• Potential Sites on Customer Property
• PV Module Inverter Selection
• Wiring Diagram
• System Economic Analysis

84
Wiring the System
85
Key Concepts of Chapter 9

• Photovoltaic system types
• Resistive loads for I-V curves
• Maximum Power Point Trackers
• Interfacing with Utility - Inverters
• NJ Incentives
• Grid Connected System Sizing
• Stand-Alone System Design

86
PV system types

• Grid Interactive and BIPV
• Stand Alone
• Pumping
• Cathodic Protection
• Battery Back-Up Stand Alone
• Medical / Refrigeration
• Communications
• Rural Electrification
• Lighting

87
Grid Interactive
88
Grid-interactive roof mounted
89
Building Integrated PV
90
Stand-Alone First House
91
Remote
92
Maximum Power Trackers
93
NJ Incentives

• NJ Clean Energy Program
• 70 rebate for grid connected systems up to 10kW
• Smaller rebates for increments above 10kW
• Net Metering to 100kW
• Solar Renewable Energy Certificates
• NJ RPF requires 2 MW 2004 ? 10 MW 2008
• Currently trading about 200/MWh

94
Economic / Market Impacts

• Systems would have 25-30 year payback
• With NJCEP reduces to 10 year
• With SREC could be less than 7 year
• Lets see an example

95
Grid Connected System Sizing

• See Solar/Electric Audit
• See Sample PV System Wiring Diagram

96
Stand-Alone PV System Design
97
New homework

• HW 8 due next Monday 11 Apr
• now posted on web
• 9.1, 9.2, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 9.11
• 9.16

98
Resistive loads and I-V curves