Photovoltaic Systems Engineering - Ali Karimpourkarimpor.profcms.um.ac.ir/imagesm/354/stories/pv/lec5_grid connected... · Photovoltaic systems engineering 6 The principles (Rule

Ali Karimpour & Reza Bakhshi 2016

2

0

16

Photovoltaic systems engineering

Photovoltaic Systems

Engineering

Reza Bakhshi

Ph.D. student

Ferdowsi University of Mashhad

Ali Karimpour

Associate Professor

Ferdowsi University of Mashhad


2

0

16


2

Lecture 5

The principles of grid connected

PV systems designing


2

0

16


The definition of GCPV system designing

Consider a PV array with the specific brand and size as well as the

inverter brand. The “designing of a GCPV system” defines as the

inverter size determination and configuration selection. In

configuration selection, the number of PV panels in each string,

number of string connected to the inverter input and number of

used input should be calculated. These electrical constraints should

be checked in order to:

3

Maximum available output energy extraction (work in MPP)

Safe performance of inverter in different weather conditions


2

0

16


4

Solar inverter Grid

Np

Ns

The definition of GCPV system designing

Design targetThe determination of:

N : number of inverters

N : the number of PV panels in each

string

N : number of string connected to the

inverter input

number of used input

inv

p

s


2

0

16


5

The principles (Rule 1)

Inverter sizing

Sizing factor = nominal DC power of PV array / nominal output power of inverter

Inverter number Sizing factor Suitable for high radiation levels

Inverter number Sizing factor Suitable for low radiation levels

Too much inverters results in non economic performance

Low inverter numbers results in inverter disconnection


2

0

16


6


Inverter sizing

Sizing factor = nominal DC power of PV array / nominal output power of inverter

This parameter should be limited to 0.8 and 1.2 (some cases in tighter interval).

In most designs, small tolerance for the PV array size can be considered in order

to find the feasible designs.

This tolerance can be 2% of the nominal power.


2

0

16


7


Inverter protection against over voltage

The lower number of series panel is limited so that even in the lowest

temperature (Vpv,OCmax), the string highest voltage, i.e. open–circuit

voltage (VOC), does not exceed the inverter maximum input voltage

(Vinv,max):

max,

max,

OCpv

inv

SV

VN

)](1[ ,min,,max, STCCCOCOCSTCpvOCpv TTVV


2

0

16


8


Inverter protection against over current

The total output current of inverter input is limited so that it is protected

from overcurrent. The worst case for string current, i.e. the most at the

maximum radiation level (Ipv,max) can be calculated as follows:

),min( max,

max,

max,

p

pv

inv

p NI

IN

STC

STCpvpvS

SII max

,max,

Maximum strings

equipped for each input


2

0

16


9


Inverter operation in MPP

An important goal of electrical constraints is to guarantee the optimal

performance of the solar system, or in other words PV array MPP voltage

optimum allocation in the inverter MPP voltage interval. This should be

done, especially in conditions of high radiation level that mostly coincides

with high temperature. To do this, the string MPP voltage of the mth input

should be greater than the lowest MPP voltage interval of the inverter

(Vinv,MPPmin):

min,

min,

MPPpv

MPPinv

SV

VN

)](1[ ,max,,min, STCCCMPPMPPSTCpvMPPpv TTVV


2

0

16


10

The summary

For a specific PV array size:

1. Determine the inverter numbers due to the sizing factor limitation

2. Divide the PV panels to the inverters

3. Calculate the minimum MPP voltage and maximum OC voltage of

PV module as well as maximum PV current

4. Determine the minimum and maximum series panel in each string

5. Determine the maximum parallel strings

6. Find Ns and Np so that Ns×Np equals to the PV panels per inverter

7. If you fail in (6), Try to change the inverter numbers and find another

Ns and Np

8. If you fail in (7), Try to change the PV array size and find Ns and Np


2

0

16


11

GCPV system design

Growatt 10000UE

Example 6.1: Design a 20 kWp GCPV system with the following PV

panel and inverter. The site location is Bojnourd with -20 °C, 45 °C and

1100 W/m as the lowest ambient temperature, highest ambient temperature

and maximum available irradiance.

2


2

0

16


12

GCPV system design

Yingli 255W


2

0

16


13

GCPV system design

Solution:

Initially, we should calculate the maximum open-circuit voltage, minimum

MPP voltages as well as the maximum MPP current.

)](1[ min,,max, STCCVOCSTCpvOCpv TTVVOC

VV OCpv 3.409.14.38)]253020()01.033.0(1[4.38max,

)](1[ max,,min, STCCVMPPSTCpvMPPpv TTVVOC

VV MPPpv 4.252.54.30)]253045()01.033.0(1[4.30min,


2

0

16


14

GCPV system design

Solution:



STC

MPPSTCpvMPPpvS

SII max

,max,

AI MPPpv 06.91000

110024.8max,


2

0

16


15

GCPV system design

Them ,the limitations on the series panel and string number should be

computed:

12 24

2

3.40

1000

4.25

300SN

06.9

20PN

06.9

20PN

3.40

1000

4.25

300SN

max,

max,

min,

min,

OCpv

inv

S

MPPpv

MPPinv

V

VN

V

V

max,

max,

MPPinv

inv

PI

IN


2

0

16


16

GCPV system design

By considering the allowable sizing factor, the feasible designs will be as

follows:

Npv Np Ns Ppv (W) Ninv Pinv (W) Sizing factor

63 3 21 16065 2 20000 0.8032

76 4 19 19380 2 20000 0.9690

80 4 20 20400 2 20000 1.0200

94 4 23, 24 23970 2 20000 1.1985

The inverter number should be 2.

Suppose we can change the PV module numbers to achieve different sizing

factor values.


2

0

16


17

GCPV system design

...

...

23

24

...

...

23

24


2

0

16


18

GCPV system design


2

0

16


19

GCPV system design


panel and inverter. The site location lowest ambient temperature, highest

ambient temperature and maximum available irradiance are -14°C, 36°C

and 1250 W/m.2

Yaskawa–Solectria Solar PVI 28TL


2

0

16


20

GCPV system design

Trina Solar TSM-PD14 310W


2

0

16


21

GCPV system design

Solution:




2

0

16


22

GCPV system design

Solution:




2

0

16


23

GCPV system design

Them , the limitations on the series panel and string number should be

computed:

16 21

4

Min (4,4)=4

Per tracker


2

0

16


24

GCPV system design

By considering the allowable sizing factor, we have:

Npv Np Ns Ppv (W) Ninv Pinv (W) Sizing factor

2100 5 21 651,000 20 560,000 1.162

2070 5 18 641,700 23 644,000 0.996

2080 5One with 20

Others with 18644,800 23 644,000 1.00

.

.

.

The feasible designs will be as follows:


2

0

16


25

GCPV system design

...

20

...

5

...

18

...

5

One with 20 series panel 22 with 20 series panel

One inverter with 20 series panel 22 inverters with 18 series panel


2

0

16


26

GCPV system design

Real project was installed in Oklahoma City (USA) at 2015.


2

0

16


27

GCPV system design


panel and inverter. The site location is somewhere with -40 °C, 30 °C and

1100 W/m as the lowest ambient temperature, highest ambient temperature

and maximum available irradiance.

2

Powador 20.0 TL3 (Kaco)


2

0

16


28

GCPV system design

TSM-PA05 - Trina Solar


2

0

16


29

GCPV system design

Solution:



)](1[ min,,max, STCCVOCSTCpvOCpv TTVVOC

VV OCpv 366.41166.42.37)]253040()01.032.0(1[2.37max,

)](1[ max,,min, STCCVMPPSTCpvMPPpv TTVVOC

VV MPPpv 02.2628.33.29)]253030()01.032.0(1[3.29min,


2

0

16


30

GCPV system design

Solution:



STC

MPPSTCpvMPPpvS

SII max

,max,

AI MPPpv 833.81000

110003.8max,


2

0

16


31

GCPV system design

Them , the limitations on the series panel and string number should be

computed:

8 24

2

366.41

1000

02.26

470SN

03.8

6.18PN

03.8

6.18PN

366.41

1000

02.26

470SN

max,

max,

min,

min,

OCpv

inv

S

MPPpv

MPPinv

V

VN

V

V

max,

max,

MPPinv

inv

PI

IN


2

0

16


32

GCPV system design

For Psys=40 kWp the panel number (Npv) are 40 kWp÷235Wp=170

Also, by considering the allowable sizing factor, we have: Ninv=2

We have two inverters, so each one should have 170÷2=85 panels.

For 4 available strings, 85÷4=21.25 panels should be considered to

every string.

To have a feasible design we connect 21 panels in 6 strings (4 strings of

1st inverter and one MPPT of the 2nd inverter) and 22 panels for

remained strings (2nd MPPT of the 2nd inverter)


2

0

16


33

GCPV system design

To have a feasible design we

connect 21 panels in 6 strings

(4 strings of 1st inverter and one

MPPT of the 2nd inverter) and

22 panels for remained strings

(2nd MPPT of the 2nd inverter)...

...

21

24

...

...

21

22

22

...

...

21

24

...

...

21

21

21

1st inverter 2nd inverter


2

0

16


Exercise

34

5.1 Present at least two designs for 30 kWp GCPV system with

following equipment:

Q Cells Q.Pro BFR-G3 250 and SMA Sunny Boy 9000TL-US

5.2 Design at least two configurations for 270 kWp GCPV system

with following equipment:

Canadian Solar CS6X-305P and Fronius Symo 24.0-3 480

5.3 Design a 5 MWp GCPV system with following equipment:

Hanwha HSL 72 305 and Eaton Power Xpert Solar 1670

Of course you need to download the datasheets from internet.


2

0

16


References

35

Bakhshi R., Sadeh J., Mosaddegh H–R., “Optimal economic designing of

grid-connected photovoltaic systems with multiple inverters using linear and

nonlinear module models based on Genetic Algorithm”, Renewable Energy,

Vol. 72, pp. 386–394, December 2014.

A. Kornelakis and Y. Marinakis, “Contribution for optimal sizing of grid-

connected PV-systems using PSO”, Renewable Energy, vol. 35, no. 6, pp.

1333–1341, June 2010.

www.solarprofessional.com

Documents

Photovoltaic Systems Engineering - Ali Karimpourkarimpor.profcms.um.ac.ir/imagesm/354/stories/pv/lec5_grid connected... · Photovoltaic systems engineering 6 The principles (Rule