pv modules and arrays

7/27/2019 PV Modules and Arrays

1/29

1FSEC

2002

Pho tovo l taic Modules and Arrays


2/29

2FSEC

2002

Photovol taic Modules and Arrays

! Typical PV modules range in size from around 0.5 m2 to

over 3 m2 surface area, with peak power output of 50 to300 watts dc. Area power densities range from 80-120

W/m2.

! Most commercially available crystalline and multi-

crystalline PV modules have 36 cells in series, and have

open-circuit voltages of 20-22 volts dc, and designed for

battery charging applications. Most listed modules can

be connected in series up to 600 volts DC.! Some thin-film modules have open circuit voltages as

high as 100 volts dc, and may use multiple parallel

module connections per source circuit.


3/29

3FSEC

2002

Current-Vo ltage (I-V) Charac teris t ic

! The current-voltage (I-V) characteristic is the basic

descriptor of photovoltaic device performance.! The I-V characteristic represents an infinite number of

current-voltage (direct-current, DC) operating points, and

varies with solar radiation and cell temperature.

! All listed PV modules are required to have certain

parameters included on module label perNEC.


4/29

4FSEC

2002

Current(A)

Voltage (V)

x

Voc

Isc

Vmp

Imp Pmp

PV Modu le or A rray I-V Curve

Power = Current x Voltage


5/29

5FSEC

2002

PV Modu le Perfo rmance Parameters

! PV module performance is given by the following

parameters:" open-circuit voltage (Voc)

" short-circuit current (Isc)

" maximum power voltage (Vmp)

" maximum power current (Imp)

" maximum power (Pmp)

" fill factor (ff)


6/29

6FSEC

2002

Module Perform ance Speci f ications

! Module performance only has meaning when the rating

conditions are specified.! All PV modules are rated at Standard Test Conditions

(STC)

" Irradiance: 1000 W/sq.m

" Cell temperature: 25 C

! Module IV parameters at STC must be on module listing

label per NEC 690.51.


7/29

7FSEC

2002

Standard Test Cond it ions (STC)

! All PV modules are rated at STC.

" Irradiance: 1000 W/m2

" Cell temperature: 25o C

! Module IV parameters at STC must be on module listing

label per NEC.


8/29

8FSEC

2002

Other Modu le Reference Cond it ions

! Standard Operating Conditions (SOC)

" Irradiance: 1,000 W/m2

" Cell temperature: NOCT

! Nominal Operating Conditions (NOC)


" Cell temperature: NOCT

! Nominal Operating Cell Temperature (NOCT)


" Ambient Temp: 20o C" PV Array: open circuit

" Wind Speed: 1.0 m/s


9/29

9FSEC

2002

Effec ts o f STC, SOC and NOC on

Typ ical IV Curve

Voltage (V)

Curren

t(A)

STC

SOC

NOC


10/29

10FSEC

2002

Response to Electr ical Load

! The electrical load connected to a PV device determines

its operating point.! For example, if a battery is connected to a PV device,

the battery voltage sets the operating voltage for that PV

device.

! In a grid-connected PV system, the inverter loads the PV

array at its maximum power point.

! The electrical load resistance that operates a PV device

at its maximum power point is equal to Vmp/Imp (ohms).


11/29

11FSEC

2002

Effect o f Resis t ive Load on PV

Module Operat ing Point

Voltage

Cu

rre

nt

Load Lines ofConstant

Resistance

Decreasing load resistance

Increasing load

resistance

Isc: R = 0

Voc: R = infinity


12/29

12FSEC

2002

Response to Load:

Example

! Q:The maximum power voltage and maximum power

current for a PV module are 15 volts and 3 amps,respectively.

! What is its maximum power and what resistive load is

required to operate the PV module at the maximum

power point?


13/29

13FSEC

2002

Response to Load:

Example (con t.)

! A:From Ohms Law, the resistance is equal to the

voltage divided by the current:15 volts / 3 amps = 5 ohms

(R = V / I)

! The power is calculated by the product of the voltageand current:

15 volts x 3 amps = 45 watts

(P = V x I)


14/29

14FSEC

2002

Response to Solar Irradiance

! Changes in irradiance (solar power) significantly affect

the current and power output of a PV device, but have amuch smaller effect on the voltage.

! The fact that the voltage varies little with changing

sunlight levels makes PV devices well-suited for battery

charging applications.


15/29

15FSEC 2002

Response to Solar Irradiance

Voltage

Cu

rren

t

1000 W/m2

750 W/m2

500 W/m2

250 W/m2

Current increases withincreasing irradiance

Voltage changes little

with irradiance

Maximum power voltage

changes little with

irradiance

IV Curves at Constant Temperature


16/29

16FSEC 2002

Response to Irradiance: Example

! Q:What would the maximum power output be under 600

W/m2 irradiance for a PV module producing 50 wattsmaximum power at 1000 W/m2?

! A:Power output is generally proportional to irradiance,

therefore the maximum power at 600 W/m2 irradiance is:

50 Watts * 600 / 1000 = 30 Watts


17/29

17FSEC 2002

Response to Temperature

! Increasing cell temperature results in a significant

decrease in voltage, however current output increasesslightly. For crystalline silicon PV devices:

" Voltage is affected by approx -0.45% per degree C

" Current is affect by approximately +0.1% per degree C

! The net effect for most PV devices is decreasing power

output with increasing cell temperature.

! Higher cell operating temperatures reduce cell output,

efficiency and lifetime. Colder operating environmentsresult in higher operating voltages.


18/29

18FSEC 2002

Response to Temperature

Voltage

Cu

rren

t

T = 25 oC

T = 50 oC

T = 0 oC

Increasing temperature

reduces voltage


reduces power output


increases current


19/29

19FSEC 2002

Sim ilar PV Dev ices in Series

! When similar devices are connected in series,

the voltages add and the current is the same asone device.

Vseries = VA + VB

Iseries = IA = IB

Pos (+) (-) (+) Neg (-)

Pos (+)

Neg (-)

A B


20/29

20FSEC 2002

I-V Curves fo r Sim ilar PV Dev ices in

Series

Voltage (V)

Curren

t(A)

A, B A + B

V = VA + VBI = IA = IB


21/29

21FSEC 2002

Sim ilar PV Dev ices in Paral lel

! When similar devices are connected in parallel, the

individual currents add, while the voltage is the same asfor one device.

A

B

Pos (+)Neg (-)

Vparallel = VA = VB

Iparallel = IA + IB


22/29

22FSEC 2002

I-V Curves fo r Sim ilar PV Dev ices in

Parallel

V = VA = VB

I = IA + IBA, B

Voltage (V)

Curren

t(A) A + B


23/29

23FSEC 2002

Bui ld ing a PV Array

! Modules are connected in series and in parallel to obtain

a desired current, voltage and power output of the array.! First, build series strings to obtain desired system

voltage.

! Next, parallel the number of strings required to achieve

the array current and power output.


24/29

24FSEC 2002

Bui ld ing a PV Array

Voltage (V)

C

urrent

(A)


25/29

25FSEC 2002

PV Modu le Perfo rmance Parameters

Current(A)

Voltage (V)

x

Voc

Isc

Vmp

Imp Pmp


26/29

26FSEC 2002

Curren t Standards Related to

Photovol taic Modules

! IEEE 1262: Recommended Practice for Qualification of

Photovoltaic (PV) Modules! UL 1703: Standard for Safety for Flat-Plate Photovoltaic

Modules and Panels

! ASTM E1036/E1036M-96e2: Standard Test Methods for

Electrical Performance of Non-concentrator Terrestrial

Photovoltaic Modules and Arrays Using Reference Cells


27/29

27FSEC 2002

PV Module Markings

! 690.51 Modules

" Modules shall be marked with identification of terminals or leadsas to polarity, maximum overcurrent device rating for module

protection, and with the following ratings:

" (1) Open-circuit voltage

" (2) Operating voltage" (3) Maximum permissible system voltage

" (4) Operating current

" (5) Short-circuit current

" (6) Maximum power


28/29

28FSEC 2002

Typ ical Module Label Requ ired by

National Elec tr ical Code

Siemens Solar IndustriesCamarillo, CA 93011

MODEL M55PHOTOVOLTAIC MODULE

AT 1000 W/M2 SOLAR IRRADIANCEAND 25oC CELL TEMPERATURE

30B9 LISTED

MAX. POWER SHORT CKT. RATED53 WATTS 3.35 A 3.05 A

MAX. SYST. OPEN CKT. V. OPEN CKT. RATED600 VOLTS 21.7 V 17.4 V

FIRE RATING SERIES FUSECLASS C 5 A

FIELD WIRING BYPASS DIODECOPPER ONLY, 14 AWG MIN. INSTALLATION GUIDEINSULATED FOR 75 C MIN. 233-701500-20

MADE IN U.S.A.


29/29

29FSEC 2002

pv modules and arrays

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