Advanced Power Systems

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Advanced Power Systems

• ECE 0909.402-01, 0909.504-01
• Lecture 9 PV Basics
• 4 April 2005
• Dr. Peter Mark Jansson PP PE
• Associate Professor Electrical and Computer
  Engineering

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admin announcements

• fortnight until Final Project Reports due
• Mid-Term returned this week
• HWs and LMs up front
• After you review project leave at front
• Electronic Copy of Your Project Proposals due to
  me by email this Wednesday

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See revised class schedule

• Posted on Web
• NEXT WEEK
• Weather dependent field trip 12 kV walk
• Final Presentation Dates
• 18 April, 25 April, 2 May, 9 May
• You May Be Called for ANY WEEK
• One Date reserved for PV system tour

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Mid Term Exam Grades

• Average 86
• Min 78
• Max 96
• HWs still outstanding, late is better than 0

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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

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Aims of Todays Lecture

• Part One complete summary of ch. 8 concepts
• PV Cells/Modules
• Overview of Chapter 9 PV System
• Short break at 600 p.m.
• Part Two
• Complete Chapter 9 Sample PV Design Calculations

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Solar Resources - Direct Beam
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Solar Resources Total Diffuse
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Key Concepts of Chapter 8

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

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Wind PV Production (96-02)
Wind production PV production
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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)

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PV cost projection

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

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LM 1

• 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.

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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

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Amorphous Si
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Amorphous Si
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Cadmium Telluride
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Multi-crystalline Si
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Multi-crystalline Si
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Single Crystal Si
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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)

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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.

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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

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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.

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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

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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)

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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

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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 ?
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LM 2

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

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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

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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

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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

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PV Module Performance

• Temperature dependence
• Nominal operating cell temperature (NOCT)

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

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

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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

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LM 3

• 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

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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

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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

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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

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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

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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

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Wiring the System
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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

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PV system types

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

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Grid Interactive
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Grid-interactive roof mounted
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Building Integrated PV
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Stand-Alone First House
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Remote
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Maximum Power Trackers
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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

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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

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Grid Connected System Sizing

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

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Stand-Alone PV System Design
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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

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Resistive loads and I-V curves