power optimization and monitoring in photovoltaic systems

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.

perry.tsao@nsc.com

For product info on Solarmagic™:Visit solarmagic.com or

Email solarmagic.com

Questions?

Perry Tsao

National Semiconductor Corp.

perry.tsao@nsc.com

For product info on Solarmagic™:Visit solarmagic.com or

Email solarmagic.com