lecture 10
TRANSCRIPT
Advanced Power Systems
ECE 09.402.02 and ECE 09.504.02Lecture 10: PV System Designs
2 April 2007
Dr Peter Mark Jansson PP PE
Project Help• This page offers many tools specifically for small wind
• http://www.renewwisconsin.org/wind/windtoolbox.html
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
PathFinder and Assistant
www.solarpathfinder.com
Sun Path diagram
Maximize your Solar Window
CURRENT-VOLTAGE (I-V) CURVE
Standard Test Conditions – (STC) 25°C (77°F) cell temperature and 1000 W/m² insolation
Important Points: Maximum Power Point ( Vmp , Imp ) Open Circuit Voltage ( Voc ) Short Circuit Current ( Isc )
Voc
VOLTAGE TERMINOLOGY
Nominal Voltage → 12 V (A PV panel that is sized to charge a 12V battery, but reads
higher than 12V)
Maximum Power Voltage (Vmax/Vmp)→17V-18V
under STC (A 12V module will read 17V 18V under MPPT conditions)
Open Circuit Voltage (Voc) → 20V-22V (This is seen in the early morning, late evening, and while testing the module)
EFFECTS OF TEMPERATUREFahrenheit To Celsius Conversion:
___˚C = (5/9)( ___˚F - 32) OR ___˚F = (9/5)( ___˚C) +32
0
0.5
1
1.5
2
2.5
5 10 15 20Volts
Am
ps
25° C30° C40° C50° C60° C70° C 80° C
3
25
Example: 25˚C = (5/9) (77˚F - 32)
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
Other I-V Curves
SunPower
WATTAGE COMPARISON
BP Solar Monocrystalline
Uni-Solar Amorphous
BP Solar Polycrystalline
Source: http://www.bp.com/solar
Source: http://www.bp.com/solar
Source: http://www.uni-solar.com
SunPower Back Contact
220 Watts ____________________________________________________________
61.4 in x 31.4 in
___________________________________________________________________
33.1 lbs.
175 Watts ____________________________________
62.8 in x 31.1 in
___________________________________________________
34 lbs.
160 Watts_____________________________________
62.8 in x 31.1 in
_______________________________________________
33.1 lbs.
64 Watts _________________________________________________ _
53.8 in x
29.2 in ______________________________________________________
20.2 lbs.
Source:www.sunpowercorp.com/
JUNCTION BOXES
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
SERIES CONNECTIONS
Loads/sources wired in series:• Voltages are additive• Current is equal
(through all parts of the circuit)• One interconnection wire is used
between two components (Negative connects with positive)
• Combined modules make a “series-string”
• Leave the series string from a terminal not used in series connection
PARALLEL CONNECTIONSLoads/sources are wired in parallel:
• Voltage remains the same
• Currents are additive• Two interconnection wires are used
between two components (positive to positive and negative to negative)
• Leave from any parallel terminal to the next system component
MODULES WIRED IN SERIES – and PARALLEL
Note: In reality, this system would require series fusing for only 2 series strings and under can go
without fusing by NEC
MODULES WIRED FOR HIGH VOLTAGE
____V
____A
17V x 8 = 136
4
Use the Same Modules
• Significant reductions in output can be observed when using dissimilar modules
• It can be done but you must be very careful in your analysis and design to see if it is worth it
DISSIMILAR MODULES IN SERIES
DISSIMILAR MODULES IN PARALLEL
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
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
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
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
Wiring the System
Utility Interactive PV
Utility Interactive with Battery
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
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
Maximum Power Trackers
NJ Incentives
• NJ Clean Energy Program• 40% rebate for grid connected systems up to
10kW• Smaller rebates for increments above 10kW
• Net Metering to 2 MW
• Solar Renewable Energy Certificates• NJ RPS requires • Currently trading about $250/MWh
Economic / Market Impacts
• Systems would have 25-30 year payback
• With NJCEP reduces to 14 year
• With SREC could be less than 10 year
• Let’s see an example…
Grid Connected System Sizing
See Sample PV System Wiring Diagram
Stand-Alone PV System Designs
Grounding
All equipment should be grounded
All Stainless and copper components – UL & outdoor rated
Bonded to an Earth ground
Specifying Inverter
1. Watts output AC – total connected watts of PV• STC Rating
2. DC voltage window – array voltage• 100-600 Volts DC typical (based on modules, Grid-tied
systems have a high voltage window)
3. Output voltage• 120V / 240V (residential)
• 120V/ 240V/ 208V/ 480V (3-phase for commercial)
4. Frequency – 60hz (U.S.) or 50 hz (Europe)
VOLTAGE INPUT FOR BATTERYLESS GRID-TIED INVERTERS
1. Series string voltage needs to fit the inverter’s input window
2. Voltage in a series string varies with temperature
3. If PV array voltage is lower than inverter’s window no energy production
4. If PV voltage exceeds inverter’s window could damage unit or void warranty
AVAILABLE GRID-TIED INVERTERS
SMASource: www.sma-america.com XANTREX
Source: www.xantrex.com
FRONIUS Source: www.fronius.com
PV POWERED Source: www.pvpowered.com
POWER ONESource: www.power-one.com
SOLECTRIASource: www.solren.com
KACOSource: www.kacosolar.com
AVAILABLE GRID-TIED (WITH BATTERIES) INVERTERS
Source: www.outbackpower.com
Grid-Tied with Batteries
OUTBACKSource: www.sma-america.com
SMA
XANTREX
Source: www.xantrex.com Source: www.beaconpower.com
BEACON
Inverter/Module Sizing Tools
• SMA• http://www.sma-america.com/#
• Fronius• http://www3.fronius.com/worldwide/usa.solarel
ectronics/support/tool.html
INVERTER SPECIFICATION EXAMPLE
Specifications for the Xantrex GT3
Maximum AC Power Output 3000 Watts
AC Output Voltage (Nominal) 240 VAC
AC Output frequency (Nominal) 60 Hz
DC Input Voltage Range 195-600 VDC
CEC Efficiency 94%
Source: www.xantrex.com/
EFFICIENCY vs. kWhOUTPUT OF INVERTER
Only looking at efficiency can be misleading, other things to consider:
1. MPPT effectiveness (Start up ability during intermittent clouds)
2. KWh output in high temperature
3. Product reliability
4. DC Voltage Window & Start-Up point
How NOT to fuse…
Assure the Hot Leg is Fused
A safe installation has only its hot or (+) conductor fused and its grounding conductor continuously bonded from appliance frames and metal boxes to ground.
How much will PV System Make?
• PVWatts Tool• http://rredc.nrel.gov/solar/codes_algs/PVWATTS/
New homework
• HW #8– due next Monday 9 Apr
• now posted on web
• 9.1, 9.2, 9.4, 9.5, 9.6
Lab Assignment 1
• Specify an 8 kw System for Atlantic City
• Where roof is south facing of 1200 SF
• And plot monthly output
• (According to PVWatts)