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Description of how power optimizers work and the benefits of monitoring in PV systems.Presented at the IEEE Santa Clara Valley Power Electronics Society meeting Jan 20, 2010.http://ewh.ieee.org/r6/scv/pels/archive/2010meetings.html
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Power Optimization and Monitoring in Photovoltaic SystemsPower Optimization and Monitoring in Photovoltaic Systems
Perry Tsao, Ph.D.
January 20, 2010
Perry Tsao, Ph.D.
January 20, 2010
OutlineOutline
• Photovoltaic (PV) System Basics– PV Cells and characteristics– Max Power Point Tracking (MPPT)– PV system mismatch– Power Electronics Architectures in PV Systems
• Power Optimizers– What is a power optimizer and how does it work?
• Monitoring systems– Why do I need a monitoring system? What could possibly go
wrong?
• Photovoltaic (PV) System Basics– PV Cells and characteristics– Max Power Point Tracking (MPPT)– PV system mismatch– Power Electronics Architectures in PV Systems
• Power Optimizers– What is a power optimizer and how does it work?
• Monitoring systems– Why do I need a monitoring system? What could possibly go
wrong?
Circuit model for a PV cellCircuit model for a PV cell
+
P
Dep
letio
n re
gion
+ + + + ++
N
- - - - - - -
Photon
+
-
IL
RS
RP
Icell
Vcell
+
-
IL proportional to # of photons generating EHPs =>
IL proportional to irradiance (W / m^2)
Under normal operating conditions:
PV Cell I-V Curve and P-V CurvePV Cell I-V Curve and P-V Curve
IL
RS
RP
Icell
Vcell
+
-
ISC
VOC
(VMP , IMP) (VMP , PMP)
• I-V and P-V curves for multicrystalline PV cell under standard test conditions
• 1000 W/m2, 27°C, air mass 1.5 (light spectrum)
Conventional Grid-tied PV arrayConventional Grid-tied PV array
Inverter
To grid
• PV Cells connected in series in a panel
• PV panels connected in series strings
• Strings connected in parallel to inverter input
• Max power point tracking function implemented in inverter
Centralized Max Power Point TrackingCentralized Max Power Point Tracking
• Inverter adjusts input impedance to keep panels at peak power setpoints Vmp and Imp
• Sometimes it’s simple…
I-V and P-V curve for unshaded panels
Centralized Max Power Point TrackingCentralized Max Power Point Tracking
…sometimes it’s complicated• Shading or other conditions can
create multiple peaks in P-V curve
I-V and P-V curve for shaded and unshaded panels
Shading 15% of panel area reduces power by 33%
Shade in Residential InstallationsShade in Residential Installations
9
Mismatch in a Commercial InstallationMismatch in a Commercial Installation
• Challenges:
– Vent pipes
– Orientation of modules
due to roof curve
• Commercial installations
often restricted in size
because of shade and
irregular roof shapes
• Challenges:
– Vent pipes
– Orientation of modules
due to roof curve
• Commercial installations
often restricted in size
because of shade and
irregular roof shapes
10
Dust and Precipitate SoilingDust and Precipitate Soiling
“Flagpole” Example – Munich, Germany“Flagpole” Example – Munich, Germany
12
Case Study – Impact of ShadingCase Study – Impact of Shading
Shade pattern Shade Power Loss- (1x9) Power Loss- (3x3)
0.15% 3.7% 1.7%
2.6% 16.7% 7%
• 9 Photowatt PW1650 panels, multi-crystalline,1.5kW
• 72 cells per panel72 cells per panel
• 4 bypass diodes (1 for every 18 cells)4 bypass diodes (1 for every 18 cells)
• Connected to a SMA Sunny Boy SB1100 grid-tied inverterConnected to a SMA Sunny Boy SB1100 grid-tied inverter
• Tested in two configurationsTested in two configurations
• Single string of 9 panels (1x9)Single string of 9 panels (1x9)
• 3 strings of 3 panels each (3x3)3 strings of 3 panels each (3x3)
Source: EFFECTS OF SHADOW ON A GRID CONNECTED PV SYSTEMN. Chaintreuil, F. Barruel, X. Le Pivert, H. Buttin, J. MertenINES R.D.I., Laboratory for Solar Systems (L2S). Proceedings of the 23rd EU PVSEC, 2008.
13
Case Study – Impact of ShadingCase Study – Impact of Shading
Shade pattern Shade Area % Power Loss- (1x9) Power Loss- (3x3)
13.9% 22.2% 36.8%
11.1% 36.5% 30.5%
12.5% 18.3% 17%
Source: EFFECTS OF SHADOW ON A GRID CONNECTED PV SYSTEMN. Chaintreuil, F. Barruel, X. Le Pivert, H. Buttin, J. MertenINES R.D.I., Laboratory for Solar Systems (L2S) Proceedings of the 23rd EU PVSEC, 2008.
How come shade affects power so much?How come shade affects power so much?
• Example: single string of 3 cells without bypass diodes• Example: single string of 3 cells without bypass diodes
• Same current through each cell
• Small currents through diodes and Rp
II11=5A=5AII11=5A=5A
II22=5A=5AII22=5A=5A
II33=5A=5AII33=5A=5A
Id1
Id3
Id2
How come shade affects power so much?How come shade affects power so much?
• Example: single string of 3 cells without bypass diodes• Example: single string of 3 cells without bypass diodes
• “Extra” current in unshaded cells flows through inherent diode
Id1 ≈ I1 - I2
• A single shaded cell reduces current and power for all cells in string
II11=5A=5AII11=5A=5A
II22=2.5A=2.5AII22=2.5A=2.5A
II33=5A=5AII33=5A=5A
Power Electronic Architectures for Grid-tied PVPower Electronic Architectures for Grid-tied PV
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPP
T
MPP
T
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPTM
PP
T
MP
PT MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
MPPT
Central inverter
String inverter
Panel inverter
Power Optimizer (Series)
String Optimizer
Power Optimizer (Parallel)
17
SolarMagic™ Power Optimizers – SM1230SolarMagic™ Power Optimizers – SM1230
PVModule
PVModule
PVModule
DC
AC
PVModule
PVModule
PVModule
PVModule
PVModule
PVModule
SolarMagic: Single String Operation Inverter InteractionSolarMagic: Single String Operation Inverter Interaction
• SolarMagic Maintains Max Power Over Inverter Voltage Range
• SolarMagic Maintains Max Power Over Inverter Voltage Range
P
Inverter VoltageMin Max
w/o SolarMagic
w/ SolarMagic
19
35.5V @ 3.8A
ExampleExample
PVPanel
PVPanel
PVPanel
PVPanel
PVPanel
200W
200W
200W
200W
200W
30V @ 6.7A
30V @ 6.7A
30V @ 6.7A
30V @ 6.7A
30V @ 6.7A
150V
0V
PVPanel
PVPanel
PVPanel
PVPanel
PVPanel
25W
135W
135W
135W
135W
6.6V @ 3.8A
35.5V @ 3.8A
150V
0V
35.5V @ 3.8A
35.5V @ 3.8A
Before After
1000
W
565W
20
33.3V @ 6A
ExampleExample
PVPanel
PVPanel
PVPanel
PVPanel
PVPanel
SM
SM
SM
SM
SM200W
200W
200W
200W
200W
30V @ 6.7A
30V @ 6.7A
30V @ 6.7A
30V @ 6.7A
30V @ 6.7A
150V
0V
PVPanel
PVPanel
PVPanel
PVPanel
PVPanel
SM
SM
SM
SM
SM100W
200W
200W
200W
200W
16.7V @ 6A
33.3V @ 6A
150V
0V
33.3V @ 6A
33.3V @ 6A
Before After
1000
W
900W
Panel output =30V @ 6.7A
Panel output =27V @ 3.7A
When to use power optimizersWhen to use power optimizers
• Mismatches– Shade– Aging– Dust / soiling / bird droppings– Different panel types– Clouds– Temperature variation across the array– Difference in reflected ambient light– Snow– Damaged panels– Difference in panel azimuth or tilt
• Design flexibility– Different string lengths– Different panel orientations
• Mismatches– Shade– Aging– Dust / soiling / bird droppings– Different panel types– Clouds– Temperature variation across the array– Difference in reflected ambient light– Snow– Damaged panels– Difference in panel azimuth or tilt
• Design flexibility– Different string lengths– Different panel orientations
Different String LengthsDifferent String Lengths
• When do you need it?– Multiple rooftops of different orientation and size
– Get more panels on your roof!
• When do you need it?– Multiple rooftops of different orientation and size
– Get more panels on your roof!
Different Orientations Within A StringDifferent Orientations Within A String
• When do you need it?– Small rooftops where only one string is practical
• Japan
• San Francisco Row House
– Rooftops with obstacles
• When do you need it?– Small rooftops where only one string is practical
• Japan
• San Francisco Row House
– Rooftops with obstacles
PV System MonitoringPV System Monitoring
• Why do I need monitoring? What could possibly go wrong? – Bad connectors– Ground faults– Panel damage– Rodent damage– Inverter failures– Blown fuses– Disconnected strings– Someone forgot to turn on the inverter– Weeds grow and create shade– Moss grows on your panels– Birds build a nest on your panels– Dirt accumulation– DC arc faults– Fires– Trees grow and create shade– Panels fall down– Theft– Wind damage– Your neighbor puts up a flagpole
• Why do I need monitoring? What could possibly go wrong? – Bad connectors– Ground faults– Panel damage– Rodent damage– Inverter failures– Blown fuses– Disconnected strings– Someone forgot to turn on the inverter– Weeds grow and create shade– Moss grows on your panels– Birds build a nest on your panels– Dirt accumulation– DC arc faults– Fires– Trees grow and create shade– Panels fall down– Theft– Wind damage– Your neighbor puts up a flagpole
It Takes a Complete Solution forMaximum System PerformanceIt Takes a Complete Solution forMaximum System Performance
Power Optimization
Monitoring Smart Management
Random Performance
Feel Good With Random Performance
Predictable But not Optimal Performance
Maximum Assured Performance (ROI)
High Performance
SolarMagic™ Power Optimization
Power Optimizer SmartPanel
SolarMagic™ Monitoring
InternetInternet
WeatherStation
SmartCombiner
AC Meter
Solar Operations
Center
SolarMagic™ Product Portfolio
InternetInternet
Power Optimizer
WeatherStation
SmartCombiner
AC Meter
SmartPanel Solar Operations
Center
String Manager
29
Thank youThank you
Questions?
Perry Tsao
National Semiconductor Corp.
For product info on Solarmagic™:Visit solarmagic.com or
Email solarmagic.com
Questions?
Perry Tsao
National Semiconductor Corp.
For product info on Solarmagic™:Visit solarmagic.com or
Email solarmagic.com
