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© ABB Group January 30, 2017| 2CDC 003 023 N0201 | Slide 2

Photovoltaic systems Technical Standards

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Photovoltaic technologyIEC and Local Standard – PV Modules

Reference TitleIEC61215 Siliconterrestrialphotovoltaic(PV)modules– Design

qualificationandtypeapproval

IEC 61646Thin-filmterrestrialphotovoltaic(PV)modules- Design qualification and type approval

IEC61730-1Photovoltaic (PV) module safety qualification - Part 1:Requirements for construction

IEC 61730-2Photovoltaic (PV) module safety qualification - Part 2:Requirements for testing

UL 1703 Standard for Flat-Plate Photovoltaic Modules and Panels

IEC61701 Saltmistcorrosiontestingofphotovoltaic(PV) modules

IEC 61345 UVtestforphotovoltaic(PV)modules

IEC 62716 Photovoltaic(PV)modules-Ammonia corrosiontesting

IEC 61853-1Photovoltaic (PV) module performance testing andenergyrating-Part 1: Irradianceand temperature performancemeasurements and power rating

EN50380Datasheetandnameplateinformationfor photovoltaicmodules

EN 50548 Junctionboxesforphotovoltaicmodules

IEC 60068-2-68Environmental testing - Part 2-68: Tests - Test L:Dustandsand

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Photovoltaic technologyIEC and Local Standard – Inverters

Reference TitleIEC 62109-1

Safety of power converters for use in photovoltaicpowersystems - Part 1:General requirements

IEC 62109-2Safetyofpowerconvertersforusein photovoltaicpowersystems-Part2:Particular requirementsforinverters

UL1741Standard for Inverters, Converters, Controllers andInterconnection System Equipment for Use WithDistributedEnergyResources

EN 50530 Overallefficiencyofgridconnected photovoltaicinverters

EN 50524

Data sheet and name plate for photovoltaic invertersThis EuropeanStandarddescribes data sheet andname plate informationforphotovoltaicinverters ingrid parallel operation

IEC62116

Utility-interconnectedphotovoltaicinverters

- Test procedure of islanding prevention measures

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Photovoltaic technologyIEC and Local Standard – EMC

Reference Title

IEC61000-3-2

Electromagnetic compatibility (EMC) - Part 3-2: Limits -Limits for harmonic current emissions(equipment inputcurrent≤16A perphase)

IEC 61000-3-12

Electromagnetic compatibility (EMC) - Part 3-12: Limits -Limits for harmonic currents produced by equipmentconnected to publiclow-voltage systems with input current >16 A and≤ 75 Aper phase

IEC61000-2-2

Electromagnetic compatibility (EMC) - Part 2-2:Environment - Compatibility levels for low-frequencyconducted disturbances andsignallinginpublic low-voltagepowersupply systems

IEC61000-3-3

Electromagnetic compatibility (EMC) - Part 3-3: Limits -Limitation of voltage changes,voltagefluctuationsandflickerinpublic low- voltagesupplysystems,forequipmentwith ratedcurrent≤16Aperphaseandnotsubject toconditionalconnection

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Photovoltaic technologyIEC and Local Standard – EMC

Reference Title

IEC 61000-3-11

Electromagnetic compatibility (EMC) - Part 3-11:Limits -Limitation of voltagechanges, voltage fluctuations and flicker inpublic low-voltage supply systems - Equipment with ratedcurrent≤75Aandsubject to conditional connection

IEC61000-6-1

Electromagnetic compatibility (EMC) -

Part6-1:Generic standards-Immunity for residential,commercialandlight-industrial environments

IEC 61000-6-2Electromagnetic compatibility (EMC) - Part6-2:Genericstandards- Immunity for industrial environments

IEC61000-6-3Electromagneticcompatibility(EMC)-Part 6-3:Genericstandards-Emissionstandard forresidential,commercialandlight-industrial environments

IEC 61000-6-4Electromagnetic compatibility (EMC) - Part 6-4:Genericstandards-Emissionstandard for -industrial environments

IEC/TR61000-3-14

Electromagnetic compatibility (EMC) - Part3-14:Assessmentofemissionlimits forharmonics, interharmonics,voltagefluctuationsandunbalancefortheconnectionofdisturbinginstallations toLV power systems

IEC/TR61000-3-6

Electromagneticcompatibility(EMC)-Part 3-6:Limits-Assessmentofemissionlimits fortheconnectionofdistortinginstallations toMV,HVandEHVpowersystems

IEC/TR61000-3-7

Electromagnetic compatibility (EMC) - Part

3-7:Limits-Assessmentofemissionlimitsfor theconnectionoffluctuating installations to MV,HVandEHVpowersystems

IEC/TR61000-3-13Electromagnetic compatibility (EMC) - Part3-13:Limits -Assessmentofemission limits for the connection ofunbalanced installations to MV,HV and EHV power systems

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Photovoltaic technologyIEC and Local Standard – Cables and Connectors

Reference TitleEN 50618 Electriccablesforphotovoltaicsystems

EN50521Connectorsforphotovoltaicsystems-Safetyrequirementsandtests

UL 6703OutlineofInvestigationforConnectorsforUseinPhotovoltaic Systems

UL 6703AOutlineof InvestigationforMulti-Pole ConnectorsforUseinPhotovoltaicSystems

CEI 20-91

Fire retardant and halogen free electric cable withelastomeric insulation and sheath for rated voltagesnotexceeding 1 000 V a.c and 1 500 V d.c for use in photovoltaicsystem (PV)

AK 411.2.3 Requirements for cables for PV systems

2 Pfg 1169 /08.2007 Requirementsforcablesforuseinphotovoltaic- systems

UL854 StandardforService-EntranceCables

2Pfg 1940 /11.12Requirements for cables for use on AC- applicationsin renewable energy systems

UL 4703 OutlineofInvestigationforPhotovoltaicWire

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Photovoltaic technologyIEC and Local Standard – Switchgears and Controlg.

Reference TitleIEC/TR 61439-0

Low-voltage switchgear and controlgear assemblies- Part 0:Guidancetospecifyingassemblies

IEC 61439-1Low-voltage switchgear and controlgearassemblies - Part 1: General rules

IEC 61439-2Low-voltage switchgear and controlgearassemblies - Part 2: Power switchgearandcontrolgear assemblies

IEC 61439-3Low-voltage switchgear and controlgear assemblies - Part 3:Distribution boards intended to beoperatedbyordinarypersons (DBO)

IEC61439-5Low-voltage switchgear and controlgearassemblies - Part 5: Assemblies for powerdistribution in public networks

IEC61439-6 Low-voltage switchgear and controlgear assemblies- Part 6: Busbar trunking systems (busways)

IEC 61439-7Low-voltage switchgear and control gear assemblies - Part 7:Assemblies for specific applications such as marinas, campingsites, market squares, electric vehicles charging stations

IEC 60947-3Low-voltage switchgear and control gear - Part 3:Switches, disconnectors, switch-disconnectors and fuse-combination units

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Photovoltaic technologyIEC and Local Standard – HV Switch. and Controlg.

Reference Title

IEC 62271-1 High-voltage switchgear and controlgear - Part 1:Common specifications

IEC62271-100High-voltage switchgear and controlgear - Part 100:Alternating current circuit-breakers

IEC62271-103High-voltage switchgear and controlgear - Part 103:Switchesfor ratedvoltagesabove 1 kVup to and including52 kV

IEC62271-200

High-voltage switchgear and controlgear -

Part 200: AC metal-enclosed switchgear and controlgearfor rated voltages above 1 kV and up to and including 52 kV

IEC62271-202High-voltage switchgear and controlgear - Part 202:High-voltage/low-voltage prefabricated substation

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Photovoltaic technologyIEC and Local Standard – Transformers

Reference TitleIEC60076-8 Power transformers - Part 8: Application guide

IEC 60076-11Power transformers - Part 11: Dry-typetransformers

IEC 60076-13Power transformers- Part 13: Self-protected liquid-filled transformers

EN 50541-1Three phase dry-type distribution transformers 50 Hz, from100 kVA to 3150kVA, withhighest voltage for equipmentnot exceeding 36 kV - Part 1:Generalrequirements

IEC 61558-1Safety of power transformers, power supplies, reactorsand similar products - Part 1: General requirements andtests

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Photovoltaic technologyIEC and Local Standard – Electrical Installation

Reference TitleIEC60364-1

Low-voltage electrical installations - Part 1: Fundamentalprinciples, assessment of general characteristics, definitions

IEC60364-4-41Low-voltage electrical installations - Part 4-41: Protection forsafety - Protection against electric shock

IEC60364-4-42Low-voltage electrical installations - Part

4-42:Protectionforsafety-Protectionagainst thermaleffects

IEC60364-4-43Low-voltage electrical installations - Part

4-43: Protection for safety - Protection against overcurrent

IEC60364-4-44Low-voltageelectrical installations -Part4-44: Protectionforsafety-Protectionagainstvoltage disturbances and electromagnetic disturbances

IEC60364-5-52Low-voltage electrical installations - Part 5-52: Selection anderection of electrical equipment - Wiring systems

IEC60364-5-53Electricalinstallationsofbuildings-Part5-53: Selectionanderectionofelectricalequipment- Isolation,switchingandcontrol

IEC60364-5-54Low-voltage electrical installations - Part 5-54: Selection anderection of electrical equipment- Earthing arrangements and protective conductors

IEC60364-6 Low-voltage electrical installations - Part 6: Verification

IEC60364-7-712

Electrical installations ofbuildings-Part

7-712:Requirements for special installations or locations - Solarphotovoltaic (PV) power supply systems

IEC/TS 62548 Photovoltaic (PV) arrays - Design requirements

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Photovoltaic technologyIEC and Local Standard – Electrical Installation

Reference TitleIEC62446

Gridconnectedphotovoltaicsystems-Minimum requirementsforsystemdocumentation, commissioningtestsandinspection

IEC 61829Crystalline silicon photovoltaic (PV) array - On- sitemeasurement of I-V characteristics

IEC 62305-1 Protectionagainst lightning - Part 1: General principles

IEC62305-2 Protection against lightning - Part 2: Risk management

IEC62305-3Protection against lightning - Part 3: Physical damage tostructures and life hazard

IEC 62305-4Protection against lightning - Part 4: Electrical and electronicsystems within structures

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Photovoltaic technologyIEC and Local Standard – Mounting structure

Reference Title

UL2703Outline of Investigation for Mounting Systems, MountingDevices, Clamping/Retention Devices, and GroundLugs forUse withFlat- Plate Photovoltaic Modules and Panels

UL 790Standard for Standard Test Methods for Fire TestsofRoofCoverings

UL 1897 Standard for Uplift Tests for Roof Covering Systems

UL2703Outline of Investigation for Mounting Systems, MountingDevices, Clamping/Retention Devices, and GroundLugs forUse withFlat- Plate Photovoltaic Modules and Panels

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Photovoltaic technologyIEC and Local Standard – Grid Connection

Reference Title

EN 50160 Voltagecharacteristicsofelectricitysupplied bypublicelectricitynetworks

EN50438Requirementsfortheconnectionofmicro- generators inparallelwithpublic low-voltage distribution networks

EN 61727Photovoltaic (PV) systems - Characteristics of the utilityinterface

IEC TS 62548: Photovoltaic (PV) arrays –Design requirements

• IEC 60228:2004, Conductors of insulated cables• IEC 60269-6, Low-voltage fuses – Part 6: Supplementary requirements for fuse-links for the

protection of solar photovoltaic energy systems• IEC 60287 (all parts), Electric cables – Calculation of the current rating• IEC 60332-1-2:2004, Tests on electric and optical fibre cables under fire conditions – Part 1-2: Test for vertical flame

propagation for a single insulated wire or cable – Procedure for 1 kW pre-mixed flame• IEC 60364-5-54:2011, Low-voltage electrical installations – Part 5-54: Selection and erection of electrical equipment –

Earthing arrangements and protective conductors• IEC 60364 (all parts), Low-voltage electrical installations• IEC 60364-4-41:2005, Low-voltage electrical installations – Part 4-41: Protection for safety –Protection against electric shock• IEC 60364-7-712:2002, Electrical installations of buildings – Part 7-712: Requirements for special installations or locations –

Solar photovoltaic (PV) power supply systems• IEC 60529, Degrees of protection provided by enclosures (IP Code)• IEC 60898-2, Circuit-breakers for overcurrent protection for household and similar• installations – Part 2: Circuit-breakers for a.c. and d.c. operation• IEC 60947-1, Low-voltage switchgear and controlgear – Part 1: General rules• IEC 60947-2, Low-voltage switchgear and controlgear – Part 2: Circuit breakers• IEC 60947-3, Low-voltage switchgear and controlgear – Part 3: Switches, disconnectors,• switch-disconnectors and fuse-combination units• IEC 61215:2005, Crystalline silicon terrestrial photovoltaic (PV) modules − Design qualification and type approval• IEC 61646, Thin-film terrestrial photovoltaic (PV) modules − Design qualification and type approval• IEC 61730-1:2004, Photovoltaic (PV) module safety qualification − Part 1: Requirements for construction• IEC 61730-2:2004, Photovoltaic (PV) module safety qualification − Part 2: Requirements for testing• IEC 62109-1:2010, Safety of power converters for use in photovoltaic power systems – Part 1: General requirements• IEC 62109-2, Safety of power converters for use in photovoltaic power systems – Part 2: Particular requirements for inverters• IEC 62305-2, Protection against lightning – Part 2: Risk management• IEC 62305-3, Protection against lightning – Part 3: Physical damage to structures and life hazard• IEC 62305-4, Protection against lightning – Part 4: Electrical and electronic systems within structures• IEC 62446, Grid connected photovoltaic systems – Minimum requirements for system documentation, commissioning tests

and inspection• EN 50521, Connectors for photovoltaic systems – Safety requirements and tests

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Photovoltaic technologyIEC and Local Standard – IEC 62548


Photovoltaic systems The solar panel


Photovoltaic technologyThe solar panel – Introduction to thr PV generator

The elementary component of a PV generator is the photovoltaic cell where the conversion of the solar radiation into electric current is carried out. The cell consists of a thin layer of semiconductor material, generally silicon properly treated, with a thickness of about 0.3 mm and a surface from 100 to 225 cm2.

Silicon, which has four valence electrons (tetravalent), is “doped” by adding trivalent atoms (e.g. boron – P doping) on one “layer” and small quantities of pentavalent atoms (e.g. phosphorus – N doping) on the other one. The P-type region has an excess of holes, whereas the N-type region has an excess of electrons.

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picture from: 1sdc007109g0202 (p8-1)



In the contact area between the two layers differently doped (P-N junction), the electrons tend to move from the electron rich region (N) to the electron poor region (P), thus generating an accumulation of negative charge in the P region. A dual phenomenon occurs for the electron holes, with an accumulation of positive charge in the region N. Therefore an electric field is created across the junction and it opposes the further diffusion of electric charges. By applying a voltage from the outside, the junction allows the current to flow in one direction only (diode functioning). When the cell is exposed to light, due to the photovoltaic effect2, some electron-hole couples arise both in the N region as well as in the P region. The internal electric field allows the excess electrons (derived from the absorption of the photons from part of the material) to be separated from the holes and pushes them in opposite directions in relation one to another. As a consequence, once the electrons have passed the depletion region they cannot move back since the field prevents them from flowing in the reverse direction. By connecting the junction with an external conductor, a closed circuit is obtained, in which the current flows from the layer P, having higher potential, to the layer N, having lower potential, as long as the cell is illuminated.

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A photovoltaic cell can be considered as a current generator and can be represented by the equivalent circuit

The current I at the outgoing terminals is equal to the current generated through the PV effect Ig by the ideal current generator, decreased by the diode current Id and by the leakage current Il.

The resistance series Rs represents the internal resistance to the flow of generated current and depends on the thick of the junction P-N, on the present impurities and on the contact resistances.

The leakage conductance Gl takes into account the current to earth under normal operation conditions.

In an ideal cell, we would have Rs=0 and Gl=0.On the contrary, in a high-quality silicon cell we have Rs=0.05.0.10Ω and Gl=3.5mS.

The conversion efficiency of the PV cell is greatly affected also by a small variation of Rs, whereas it is much less affected by a variation of Gl.

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The open circuit voltage Voc occurs when the load does not absorb any current (I=0) and is given by the relation:

The diode current is given by the classic formula for direct current:

Then, the current supplied to the load is given by:

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Photovoltaic module technologyThe solar panel – Introduction to thr PV generator

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The voltage-current characteristic curve of a PV module is shown in Figure. Under short circuit conditions the generated current is at the highest (Isc), whereas, with the circuit open, the voltage (Voc = open circuit voltage) is at the highest.

Under the two above mentioned conditions, the electric power produced in the cell is null, whereas under all the other conditions, when the voltage increases, the produced power rises too: at first it reaches the maximum power point (Pm) and then it falls suddenly near to the open circuit voltage value.

Then, the characteristic data of a PV module can be summarized as follows:

• Isc short-circuit current;

• Voc open circuit voltage;

• Pm maximum produced power under standard conditions (STC);

• Im current produced at the maximum power point;

• Vm voltage at the maximum power point;

• FF filling factor: it is a parameter which determines the form of the characteristic curve V-I and it is the ratio

between the maximum power and the product (Voc . Isc ) of the no-load voltage multiplied by the short-circuit

current.

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The voltage-current characteristic curve of a PV module is shown in Figure. Under short circuit conditions the generated current is at the highest (Isc), whereas, with the circuit open, the voltage (Voc = open circuit voltage) is at the highest.

Under the two above mentioned conditions, the electric power produced in the cell is null, whereas under all the other conditions, when the voltage increases, the produced power rises too: at first it reaches the maximum power point (Pm) and then it falls suddenly near to the open circuit voltage value.

Then, the characteristic data of a PV module can be summarized as follows:

• Isc short-circuit current;

• Voc open circuit voltage;

• Pm maximum produced power under standard conditions (STC);

• Im current produced at the maximum power point;

• Vm voltage at the maximum power point;

• FF filling factor: it is a parameter which determines the form of the characteristic curve V-I and it is the ratio

between the maximum power and the product (Voc . Isc ) of the no-load voltage multiplied by the short-circuit

current.

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The photovoltaic module (cells) is based on the fact that some semiconductive materials -if properly treated - can convert solar radiation directly into DC electricity (with no moving mechanics)

© ABB Group January 30, 2017 | Slide 24

Photovoltaic module technologyThe solar panel – Different type of Panels

| Slide 25

In the world of photovoltaic (PV) solar power, there are several types of semiconductor technologies currently in use for PV solar panels. Two, however, have become the most widely adopted: crystalline silicon and thin film.

Crystalline Silicon

Monocrystalline Silicon

Multicrystalline (or Polycrystalline)

Silicon

Thin Film

Cadmium Telluride (CdTe)

Amorphous Silicon

Copper, Indium, Gallium,

Selenide (CIGS)

Homogeneous crystal structure silicon (wafer)

Commercial module efficiency: 18-20%

Heterogeneous crystal structure silicon (wafer)


Copper Indium Gallium Selenide

Commercial module efficiency: 11.5-13%

Cadmium TellurideCommercial module efficiency: 11-12.5%

Amorphous or microcrystalline

silicon deposited on a substrate


Photovoltaic module technologyThe solar panel – Different type of Panels

Cell

PV Panel60-72-96

Cell

String/ArraySeveral panels

connected in series

Photovoltaic generatorDifferent string connected in parallel to

obtain the required power

Photovoltaic module technologyHow the panels are connected



Standard modules Mostly consist of 32 to 72 cells Interconnection of cells add up to a module

Series and parallel connection Parallel connection Current increase Series connection Voltage increase


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picture: Grafik_4_E-V2


Parallel connection

Current increases

Possibility of reverse current is given

Series connection

Voltage increases

Increase system voltage of the PV generators to the usable voltage


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Presentation Notes

picture: Grafik_5a_E-V2 / Grafik_5b_E-V3


Photovoltaic technologySTC (Standard Test Conditions) for PV modules

All data-sheet values of a PV module are measured at STC

STC defined in IEC 60904-2:

Irradiance of 1000 W/m² at module level

Temperature of a solar cell constant at 25 °C

Spectrum of light after passing through the 1.5 x thickness of the atmosphere (AM 1.5)

STC provide the conditions for laboratorymeasurements which become comparable due to the defined STC

Photovoltaic module technologyThe PV panels

All data-sheet values of a PV module are measured at STC(defined in IEC 60904-2):•Irradiance of 1000 W/m² at module level•Temperature of a solar cell constant at 25 °C •Spectrum of light after passing through the 1.5 x thickness of the atmosphere (AM 1.5)STC provide the conditions for laboratorymeasurements which become comparable due to the defined STC

Photovoltaic module technologyThe PV panels


Photovoltaic systems Different solar system

Stand-alonePV system

Grid connected PV system

not connection with the network grid

PV system type What is it?

Only Touching grid for voltage reference of V/Hz

Where?

Not in vicinity of pubblic grid

All the case (network grid)

Produce energy for own consumption.

Produce energy for own consumption and/or Produce energy to sell

consumption by anyone connected to grid.

Touching grid for voltage reference of V/Hz and feeding

back energy to the grid

Hybrid PV system not connection with the network grid All the case (network grid)

Produce energy for own consumption and/or Produce energy to sell

consumption by anyone connected to grid.

Disel genset + Battery?+Grid

Photovoltaic module technologyDifferent Type of PV System


Photovoltaic plant technologyGrid connected vs Off-grid/Stand alone plants

Off-grid:Produce energy for own consumption.

Grid connected:Produce energy to sell.Consumption by anyoneconnected to grid.


Photovoltaic plant technologyStand-alone systems

Stand-alone plants are mainly used to supply electricity to off-grid utilities that are away from the electrical network and difficult to reach as they are situated in areas which are hard to access or where energy consumption is too low to allow for a grid connection. In these plants, the energy produced by photovoltaic panels must be stocked by means of batteries to ensure continuous operation during the night or when the sun is not shining.

These small plants can be totally powered by direct current.

To obtain alternate current power, an inverter is needed.

Photovoltaicgenerator

Battery

Chargeregulator

DC Loads

AC Loads

DC/AC Inverter


Grid-connected plants are connected in parallel with the public network and are designed to supply the energy produced. Therefore, they work as small power plants and can fully or partially meet the energy requirements of public, industrial or private buildings.

These plants feature a surface including a number of interconnected photovoltaic modules with special devices that supply power to an inverter.

The inverter adjusts the energy produced by the photovoltaic power to the network standards - either single-phase or three-phase - and conveys it to the network.

Photovoltaic generator

Network

Meter

Energy produced

LoadMeter

Network exchange

Photovoltaic plant technologyGrid-connected systems


Photovoltaic systems DC part how to size


Photovoltaic technologyDC Part How to size - Voltage and current

PV modules generate a current from 4 to 10A at a voltage from 30 to 40V.

To get the projected peak power, the modules are electrically connected in series to form the strings, which are connected in parallel.

The trend is to develop strings constituted by as many modules as possible, because of the complexity and cost of wiring, in particular of the paralleling switchboards between the strings.

The maximum number of modules which can be connected in series (and therefore the highest reachable voltage) to form a string is determined by the operation range of the inverter and by the availability of the disconnection and protection devices suitable for the voltage achieved. In particular, for efficiency reasons, the voltage of the inverter is bound to its power: generally, when using inverter with power lower than 10 kW, the voltage range most commonly used is from 250V to 750V, whereas if the power of the inverter exceeds 10 kW, the voltage range usually is from 500V to 900V.

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Photovoltaic technologyDC Part How to size - Variation in the produced energy

The main factors which influence the electric energy produced by a PV installation are:

Irradiance.

Temperature of the modules. Shading.

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Photovoltaic technologyDC Part How to size - Irradiance

As a function of the irradiance incident on the PV cells, their characteristic curve V-I changes as shown in Figure.

When the irradiance decreases, the generated PV current decreases proportionally, whereas the variation of the no-load voltage is very small.

As a matter of fact, conversion efficiency is not influenced by the variation of the irradiance within the standard operation range of the cells, which means that the conversion efficiency is the same both in a clear as well as in a cloudy day. Therefore, the smaller power generated with a cloudy sky can be referred not to a drop of efficiency, but to a reduced production of current because of lower solar irradiance.

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Photovoltaic technologyDC Part How to size - Temperature of the modules

Contrary to the previous case, when the temperature of the PV modules increases, the current produced remains practically unchanged, whereas the voltage decreases and with it there is a reduction in the performances of the panels in terms of produced electric power

The variation in the open circuit voltage Voc of a PV module, with respect to the standard conditions Voc,stc, as a function of the operating temperature of the cells Tcell, is expressed by the following formula:

where:

- β is the variation coefficient of the voltage according to temperature and depends on the typology of PV module;

- Ns is the number of cells in series in the module.

Therefore, to avoid an excessive reduction in the performances, it is opportune to keep under control the service temperature trying to give the modules good ventilation to limit the temperature variation on them. In this way it is possible to reduce the loss of energy due to the temperature .

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Photovoltaic technologyDC Part How to size - Shading

Taking into consideration the area occupied by the modules of a PV plant, part of them (one or more cells) may be shaded by trees, fallen leaves, chimneys, clouds or by PV modules installed nearby. In case of shading, a PV cell consisting in a junction P-N stops producing energy and becomes a passive load. This cell behaves as a diode which blocks the current produced by the other cells connected in series and thus jeopardizes the whole production of the module. Besides, the diode is subject to the voltage of the other cells; this may cause the perforation of the junction because of localized overheating (hot spot), and damages to the module. In order to avoid that one or more shaded cells thwart the production of a whole string, some diodes which by-pass the shaded or damaged part of module are inserted at the module level. Thus, functioning of the module is guaranteed but with reduced efficiency. In theory, it would be necessary to insert a by-pass diode in parallel to each single cell, but this would be too onerous for the ratio costs/benefits.

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Photovoltaic technologyDC Part How to size

There are two problems with voltage drop in PV systems.

First, it represents wasted energy. Transforming electrical energy into heat in circuit conductors is lost energy production.

Second, voltage drop can cause PV inverters to stop working properly under certain conditions. For example, if the dc bus voltage drops below the inverter’s minimum MPPT voltage, then the inverter will operate in a limited state. If the ac bus voltage rises above the maximum grid voltage set point, then the inverter will stop operating completely.

What you can do?

You can optimize the schematic design and layout of equipment strategically to minimize voltage drop. You can also consider upsizing certain system conductors to further reduce voltage drop.

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The cables used in a PV plant must be able to stand, for the whole life cycle (20 to 25 years) of the plant, severe environmental conditions in terms of high temperatures, atmospheric precipitations and ultraviolet radiations. First of all, the cables shall have a rated voltage suitable for that of the plant.

The conductors8 on the DC side of the plant shall have double or reinforced isolation (class II) so as to minimize the risk of earth faults and short-circuits (IEC 60364- 712).

The cross sectional area of a cable shall be such as that:

• its current carrying capacity Iz is not lower than the design current Ib;

• the voltage drop at its end is within the fixed limits.

Under normal service conditions, each module supplies a current near to the short-circuit one, so that the service current for the string circuit is assumed to be equal to:

where Isc is the short-circuit current under standard test

conditions and the 25% rise takes into account radiation

values higher than 1kW/m2.

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When the PV plant is large-sized and divided into subarrays, the PV sub-array cables shall carry a design current equal to:

where SSA is the number of strings of the sub-array relating to the same PV string combiner box.

The current carrying capacity Io of the cables is usually stated by the manufacturers at 30°C in free air. To take into account also the methods of installation and the temperature conditions, the current carrying capacity Io shall be reduced by a correction factor (when not declared by the manufacturer) equal to:

• k1 = 0.58 . 0.9 = 0.52 for solar cables

• k2 = 0.58 . 0.91 = 0.53 for non-solar cables.

The factor 0.58 considers the installation on the rear of the modules where the ambient temperature reaches 70°C10, the factor 0.9 the installation of solar cables in conduit or trunking system, while the factor 0.91 refers to the installation of non-solar cables into conduit exposed to sun.

In PV plants the accepted voltage drop is 1% to 2% (instead of the usual 4% of the user plants) so that the loss of energy produced due to the Joule effect on the

cables is limited as much as possible.

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Photovoltaic technologyDC Part How to size - Voltage Drop

The resistance of a given object depends primarily on two factors:

What material it is made of, and its shape.

The value of the resistance of a conductor of uniform cross section, therefore, can be computed as:

L = length in meter of the conductor (in DC side 2 time the length of + cable) (mt)

r = electrical conductivity (S/mt)

A = section of the conductor

The electrical resistivity of most materials changes with temperature. In particular with linear aprox.:

α = Temperature coefficient of resistivity

r0= electrical conductivity at ambient temperature

T0 = pormal ambient temperature (20degree)

T= working temperature

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Presentation Notes



Photovoltaic technologyDC Part How to size - Voltage Drop (Ohm Law)

The resistance of a given object depends primarily on two factors:

What material it is made of, and its shape.

The value of the resistance of a conductor of uniform cross section, therefore, can be computed as:

L = length in meter of the conductor (in DC side 2 time the length of + cable) (mt)

r = electrical conductivity (S/mt)

A = section of the conductor

The electrical resistivity of most materials changes with temperature. In particular with linear aprox.:

α = Temperature coefficient of resistivity

r0= electrical conductivity at ambient temperature

T0 = pormal ambient temperature (20degree)

T= working temperature

Presenter

Presentation Notes



Photovoltaic systems PV Inverter Sizing


Photovoltaic technologyInverter Sizing

The size of the inverter can be determined starting from a value from 0.8 to 0.9 (𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃

) for the ratio between the active power put into the network and the rated power of the PV generator.

Keeps into account the loss of power of the PV modules under the real operating conditions (working temperature, voltage drops on the electrical connections….) and the efficiency of the inverter.

This ratio depends also on the methods of installation of the modules (latitude, inclination, ambient temperature…) which may cause a variation in the generated power. For this reason, the inverter is provided with an automatic limitation of the supplied power to get round situations in which the generated power is higher than that usually estimated.

Presenter

Presentation Notes



Photovoltaic technologyInverter Sizing – Real Example with simulation software

Presenter

Presentation Notes


SOLAR INITIATIVE OVERVIEWSchematic PV Plant - Factors impacting efficiency

Panels

DC circuits

DC/AC conversion

AC power


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