Photovoltaic Systems Engineeringkarimpor.profcms.um.ac.ir/imagesm/354/stories/pv/lec3...Ali...

Ali Karimpour & Reza Bakhshi 2016

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Photovoltaic systems engineering

Photovoltaic Systems

Engineering

Reza Bakhshi

Ph.D. student

Ferdowsi University of Mashhad

Ali Karimpour

Associate Professor

Ferdowsi University of Mashhad


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2

Lecture 3

PV cell model


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Diode

P-N junction in forward biased

3

10

kT

qV

d eII

I0 is the reverse saturation current (A), V is the voltage across the diode (V)

q is the electron charge (1.602×10-19 C)

T is the junction temperature in Kelvin (K)

k is the Boltzmann’s constant (1.381×10-23 J/K)


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Solar cell model

4

Diode current (Shockley)

Component of currentdue to photons

10

kT

qV

d eII

10

kT

qV

l eIII

lI


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5

Solar cell model

10

kT

qV

l eIII


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I-V characteristics of PV cell

V-I equation:

6

Open circuit voltage:

Short circuit current:

10

kT

qV

l eIII

00

0 lnlnI

I

q

kT

I

II

q

kTV ll

oc

lsc II


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7

Maximum power of a PV cell is labeled as the maximum power point

(MPP). The power, voltage and current corresponding to this point are

named P , V and I .

Characteristics of PV cell (Maximum power)

MPP MPPMPP


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8

)1(0

kT

qV

l eIIVP

I-V characteristics of PV (Power)


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9

STC and NOCT

STC: Standard test condition

It is the cell temperature equals to 25°C, at AM 1.5 irradiance conditions,

G=1.0 kW/m2.

The PV cell performance depends mainly to temperature and irradiance.

The characteristics and performance of PV cells have been presented in two

conditions:

NOCT: Nominal Operating Cell Temperature

It is the cell temperature at an ambient temperature 20°C, at AM 1.5

irradiance conditions, G=0.8 kW/m2 and a wind speed less than 1 m/s.


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10

PV cell temperature computation

For PV cell analysis, we need to determine its temperature. Since the ambient

temperature (T ) data rather than the cell temperature is available, the relation

between these two parameters is needed. The cell temperature can be determined

by two following equations:

A

GTT AC

8.0

20NOCT

30 AC TT


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The cell current relates linearly to the illumination level, whereas its

voltage is approximately independent of irradiance.

1.5 AMat kW/m1),(/)( 2

0 STCSTCSTC GGIGGGI


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The cell temperature rise results in voltage and power decreases. Also, it

doesn't roughly affect the PV cell current. The temperature influence have

been determined by some temperature coefficients presented in the

datasheet.


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Temperature coefficient

Short circuit current (α) 0.04 %/˚C

Open circuit voltage (β) -0.46 %/˚C

Maximum power point power (γ) -0.32 %/˚C

In some cases, the temperature

coefficient of maximum power

point voltage has also been

presented.


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13

The PV cell voltage and current in STC have been presented in the

datasheet. The voltage and current in any arbitrary radiation and

temperature level can be easily computed by temperature coefficients

and following relations:

Voltage and current calculation

1

21122 )()(

G

GGIGI

)](1[)( STCSTC TTVTV This equation is valid for both MPP and

open circuit voltages.

)](1[),( STCSTC

STC TTG

GPGTP

This equation is valid for both MPP and

short circuit currents.


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Power versus voltage for a PV cell for 4 illumination levels

PV cell power by irradiance


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Temperature dependence of the power vs. voltage curve for a PV cell

C0.5%/ decreasepower Cell

PV cell power by temperature


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Cell, Module and Array

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Below5 W

5-more than 300 W 100-Kw range


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Suitable for

12 V Battery

Suitable for

24 V Battery

Cell, Module and Array (Making a module)


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Blocking diode

Cell, Module and Array (Blocking diode)


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Bypass diode

Cell, Module and Array (Bypass diode)


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Combine bypass diode and blocking diode

Blocking

diode

Bypass

diode

Cell, Module and Array


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Sample PV module datasheet (QCell company)

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Example


Find the MPP current, voltage and power of the STP 275S modeule

manufactured by Suntech company in the 750 W/m and 45 °C2


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Example


1

21122 )()(

G

GGIGI

)(9852.28)1148.2(1.31)45(

)]2545()01.034.0(1[1.31)45(

VV

V

)](1[),( STC

STC

STC TTG

GPGTP

2

)(6375.61000

75085.8)750(2 AI



)](1[)( STCSTC TTVTV

)(39.1926375.69852.28 WIVP MPPMPPMPP


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Example


)](1[),( STC

STC

STC TTG

GPGTP

2



)(3375.189

)]2545()01.041.0(1[1000

750275)/750,45( 2

W

mWCP


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25

10

kT

qV

l eIII

AISC 2

V0.596V if

OC

83.0FF

0.82-0.5

Cell Real

I-V characteristics of PV (Fill factor)


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PV cell conventional models

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PV Conventional Model

Rs : Semiconductor material, the

metal grid, collecting bus.

Rp : Small leakage of

current through a resistive

path in parallel with the

intrinsic device.

The more accurate model


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Equivalent circuit parameters calculation

27

Deriving equivalent circuit parameters

SCSC II measure then 0VLet ?


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Deriving equivalent circuit parameters



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Changing parameters in a PV cell



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Maximum power of a PV module is not equal with n*maximum power of one cell.

At SC condition one cell produce power and one cell dissipate this power.



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For other equipment, the efficiency shows the ration of output work (power) to the

input energy (power). This parameter shows the required area to produce specified

STC power for photovoltaic systems.

Efficiency concept

31

Consider two 200Wp panels with 10% and

20% efficiencies. The area of these modules

can be easily computed:

STC: 1000 W per m2

2

Module 1: Power per m =1000×0.1=100 W

So, required area for 200 W is 2 m

This value is 1 m for Module 2.

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2

Higher efficiency shows lower required area

to produce a specific power in STC.


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Exercise

32

3.1. Voltage and current of a module with 36 cells are given in the next slide.

(At 1 kW/m2, 25 ºC)

a) Plot V-I curve.

b) Determine Isc and Voc.

c) Plot the P-V curve for the cell.

d) Find Pmax of the module.

e) Find parameters of equivalent circuit.

f) Find reverse saturation current.

g) Determine RL(Load resistance) to work in maximum power.

i) Repeat a, c, d, g at 0.4 kW/m2.

h) Plot V-I curve of the derived model and compare it with part a


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Exercise

34

3.2. Consider a PV module with following characteristics. Figure presented in

next slide shows a daily irradiance and temperature curves at the location that PV

module has been installed.

a) Compute the output power of PV module for every hour and plot the output

power graph.

b) Determine the daily available energy and generated energy.

c) Calculate the peak sun hours.


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Exercise

35

Inso

lati

on

le

ve

l

Am

bie

nt te

mp

era

ture

1000

600

500

350350

200 200 5

10

15

20

25

8 10 12 14 16 179 11 13 15


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References

36

V. L. Brano, A. Orioli, G. Ciulla and A. di Gangi, “An improved five-

parameter model for photovoltaic modules”, Solar Energy Materials and Solar

Cells, vol. 94, no. 8, pp. 1358–1370, August 2010.

M. G. Villalva, J. R. Gazoli and E. R. Filho, “Comprehensive approach to

modeling and simulation of photovoltaic arrays”, IEEE Transactions on

Power Electronics, vol. 24, no. 5, pp. 1198–1208, 2009.

www.q-cells.com

Photovoltaic Systems Engineeringkarimpor.profcms.um.ac.ir/imagesm/354/stories/pv/lec3...Ali...

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