Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out

UTILITY ASPECTS OF GRID CONNECTED PHOTOVOLTAIC POWER SYSTEMS

VIEWS: 40 PAGES: 10

  • pg 1
									                       IEA PVPS
             International Energy Agency
Implementing Agreement on Photovoltaic Power Systems



                       Task V
      Grid Interconnection of Building Integrated
   and Other Dispersed Photovoltaic Power Systems




                Report IEA PVPS T5-01:1998



UTILITY ASPECTS OF GRID CONNECTED
  PHOTOVOLTAIC POWER SYSTEMS



                          December 1998




                            Prepared by:
                           Bas Verhoeven
                       KEMA Nederland B.V.
                 Utrechtseweg 310, P.O.box 9035
                6800 ET, Arnhem, The Netherlands
                 email : s.a.m.verhoeven@kema.nl




      To obtain additional copies of this report or information on other
    IEA-PVPS publications, contact the IEA website: http://www.iea.org
Utility Aspects of Grid Connected Photovoltaic Power Systems                      Page 14-119



14. CONCLUSIONS AND RECOMMENDATIONS

The conclusions and recommendations of the individual subjects are given at the end of
each chapter.

Table 1 shows an overview of the subjects that can be categorised as “solved”. For these
subjects the number of remaining technical questions is (nearly) zero. Some of the subjects
grouped in the column “solved” may however still be under discussion in some countries. For
those situations the information provided in this report may be used as an international
reference.

Table 1        Overview of the technical status of the subject described in this report
 “Solved”                                        Need for further research
 · Harmonics for single inverter                 · Harmonics with multiple inverters
 · AC Modules                                    · Effects on power network with multiple
                                                   inverters
 · Grounding and ground fault detection of
   PV-systems                              · Islanding of inverters in a part of the
                                             network
 · Lightning induced overvoltages
 · EMI of inverters
 · Reclosing
 · External disconnect
 · Isolation transformer and DC-injection

From the table it must be concluded that the issue of multiple PV-inverters is the main
unresolved subject. It is advised to continue to study the behaviour of multiple inverters and
the effects of high penetration levels of PV-systems in a relatively small electrical network,
for example a residential area. The need for this research is clearly identified in almost all
Task V participating countries. Examples can be found in the Olympic village in Australia, the
village S• ringen in Denmark and a residential area with 1 MW in the Netherlands.




Report IEA-PVPS T5-01:1998
Utility Aspects of Grid Connected Photovoltaic Power Systems                                                             Page 17-144



17. ANNEX B SYSTEM GROUNDING SUMMARY
The requirements for grounding of PV system components and PV systems are often the least understood design parameter in the system. PV Systems may be required to be grounded, double insulated, or may not
require a system ground. The rules for grounding may depend on system size or categories of installations, such as low voltage, self contained, or utility-tied. The following lists the requirements for grounding of PV
systems in eight participating IEA countries.

Topic                              Requirement or Comment By Country
                                   Australia         Austria                Germany              Italy               Japan                Netherlands         Switzerland          United Kingdom      United States
PV Array Grounding                 Equipment         Recommended            Recommended          Equipment           Equipment            Equipment           Equipment            Required            Equipment
Requirements (Conductive           Ground            for lightning,         for Lightning.       Ground              Ground               Ground              Ground               (IEE Regulations    Ground
Frame)                             Required          Prohibited for         Prohibited for       Required            Required             Required            Required             BS7430)             Required
                                                     certain                Certain              CEI-ETD                                                                           Note: PME           NEC
                                                     protection             protection                                                                                             Earth Should not
                                                     classes                classes                                                                                                be taken outside
                                                                             DE- VDE0100                                                                                           of Building
                                                                            Part 712 Draft
PV Source Circuit Grounding        Ground Not           Depends on          Depends on           No Requirement      No Grounding         Not required,       Grounding Not        Grounding Not       Grounding
Requirements                       Required             earthing and        earthing and         for Grounding       Requirement          normal practice     Specified            Specified           Required for
                                                        isolation           isolation                                                     is to have                                                   >50V
                                                        transformer         transformer                                                   floating DC
                                                                                                                                          circuit
Batteries Associated with PV       No Grounding         None                Grounding Not        None                No Grounding         Grounding Not       Grounding Not        Grounding Not       Grounding is
Array                              requirements if                          Required                                 Requirements         Required            Specified            Specified           Required where
Grounding Requirements             fuse in both +                                                                                                                                                      non-qualified
                                   and earth                                                                                                                                                           personnel have
                                   connections                                                                                                                                                         access for >50V.
Conductive Battery Support         None                 Required            Grounding            Grounding           None                 Grounding           Grounding            Grounding           Grounding
Structure Ground Requirements                                               Required             Required                                 Required            Required             Required            Required
Inverter with Conductive case,     Case Grounding       Depends on          Depends on           Case Grounding      Case Grounding       Metal case must     Grounding            Grounding           Case Grounding
Grounding Requirement              Required)            protection class    protection class     Required            - Required           be grounded.        Required             Required            - Required
Inverter Active Circuit            Neutral              Depends on          Depends on           Active Circuit -    Active Circuit       Not required,       Grounding Not        Grounding Not       Active circuit
Conductors                         Grounded             system              earthing &           No Requirement      No Grounding         normal practice     Specified            Specified           Grounding
                                   (MEN System          configuration       isolation                                Required             is floating DC                                               Required for
                                                                            transformer                                                                                                                >50V
Are Center-Tapped DC Systems       Yes                  Not discussed       Yes                  Yes                 Not Decided          Yes                 Yes                  Yes                 Yes
Allowed
Are High Resistance Grounds        Not Generally        No                  No, (Not             Yes                 No ( In              No                  Yes                  Yes, Earth          Yes
Allowed                                                                     mentioned)                               Principle)                                                    leakage
                                                                                                                                                                                   detection
                                                                                                                                                                                   required




Report IEA-PVPS T5-01:1998
Utility Aspects of Grid Connected Photovoltaic Power Systems                                                   Page 17-145

System Grounding Summary (Continued)

Topic                           Requirement or Comment By Country
                                Australia         Austria             Germany              Italy               Japan         Netherlands     Switzerland     United Kingdom     United States
DC/AC Ground Intertie (Bond)    Not Specified     Yes                 Depends on                               Not Decided   Not specified   Not Specified   Not Specified      Required
Grounding Requirements                                                earthing system
                                                                      but varies from
                                                                      isolation to bond.
Are Ground Fault Detectors      No, but generally                     No                   No, but generally   Yes           Yes, for DC-    No              Not Specified      Yes, for
Required on DC Circuits         used on large                                              used on MV                        voltage > 120                                      systems
                                systems                                                    systems                                                                              mounted on
                                                                                                                                                                                dwellings
Are Ground Fault Detectors      Yes                 No                No                   Yes                 Yes           No              Not Mandatory   Yes,               Yes
Required on AC Circuits                                                                                                                                      Requirement is
                                                                                                                                                             for
                                                                                                                                                             Disconnection
                                                                                                                                                             Times to be Met
Are DC-Side Transient           Not Specified       Yes, Class C      No, but              No, but used by     Yes           Recommended     Yes             Not Specified      No, but
Suppressers Required                                                  recommended          ENEL                                                              General Practice   generally used
                                                                                                                                                             to Include
Are AC -Side Transient          No                  No                No                   Yes                 Yes           No              Yes             Not Specified      No, but usually
Suppressers Required                                                                                                                                                            used
Is Charge Controller/System     Not Mentioned       Depends on        Not Mentioned                            Required      Not mentioned   Not Specified   Not Specified      Required with
Controller Grounding Required                       system. Usually                                                                                                             exceptions for
                                                    No                                                                                                                          current limited
                                                                                                                                                                                systems and for
                                                                                                                                                                                systems >50V.

Comments




Report IEA-PVPS T5-01:1998
Utility Aspects of Grid Connected Photovoltaic Power Systems                                                          Page 17-149

PV Array
PV Arrays may be ground-mounted, roof-mounted or become part of a building as a facade or awning. This table addresses the wiring and grounding requirements for the PV array installation.

Topic                             Requirement or Comment By Country
                                  Australia         Austria               Germany             Italy               Japan               Netherlands         Switzerland         United Kingdom   United States
PV Source Circuit Grounding       No grounding      Depends on            Depends on          No grounding        No grounding        No grounding        No grounding                         Grounding
Requirements                      requirements      earthing system       Earthing System     requirements        requirements        requirements        requirements                         Required
                                                                                                                                                                                               Grounding may
                                                                                                                                                                                               be a resistance
                                                                                                                                                                                               ground
Metal Frame                       Yes                 Grounding           Grounding           Yes, Using          Required            Yes                 Yes                                  Required
Grounding/Bonding                                     generally           generally           standardized
                                                      recommended.        recommended.        components
                                                      Prohibited with     Prohibited with
                                                      certain             certain
                                                      protection          protection
Frameless or Non-conductor        Not Regulated       Not regulated.      Not Regulated.      None                Not Mentioned       Not regulated       None                                 Metal structure
frame Module Requirements                             Class II            Class II                                                                                                             must be
                                                      suggested           suggested                                                                                                            grounded.
Blocking Diode Requirements       None                Required. May       Required. May       None, but           Required            None                None                                 Not Required.
                                                      be omitted with     be Omitted with     practiced by        (Possible to
                                                      Class II modules    Class II modules.   ENEL                Remove)
Bypass Diode Requirements         General Practice    According to        According to        General Practice    Required            None                General Practice.                    Not Required
                                                      Manufacturer        Manufacturer                            (Possible to                            (Module
                                                      specifications.     Specs                                   Remove)                                 supplier
                                                                                                                                                          requirement)
Allowable Open Circuit Voltage    Not Specified       Not discussed.      1500V. 120 V        600V for LV         750 V (JIS deals    Max 1500 Vdc        Depends on                           600 Volts for
for Array                                             Depends on          for Class III       50V for passive     only with under     according to IEC    Product                              One and Two-
                                                      Module              Systems.(Vdc 0-     safety              750V dc             364                 Specification                        family dwellings.
                                                      Specification       100)                                    Voltage)                                                                     other systems
                                                      (usually 600V)                                                                                                                           limited to 1000V
                                                                                                                                                                                               listing limit.
Wire Insulation Types Allowed     Must pass           Not Specified,      Not Specified,      Certified           IV (Poly-vinyl)     Cables must be      Not Specifically,                    Types USE, UF,
                                  compliance tests    but cables must     but cables must                         CT (Rubber)         suitable for        but cables must                      SE permitted.
                                  for UV, heat etc.   withstand           withstand                               CV-CE               application.        withstand                            Where exposed
                                                      expected            expected                                (Polyethylene)      Double              expected                             to sunlight, USE,
                                                      ambient and         ambient                                                     insulation          ambient                              UF, or others
                                                      outdoor             conditions                                                                      conditions                           listed & marked
                                                      conditions                                                                                                                               sunlight resistant




Report IEA-PVPS T5-01:1998
Utility Aspects of Grid Connected Photovoltaic Power Systems                                                          Page 17-150

PV Array (Continued)

Topic                            Requirement or Comment By Country
                                 Australia         Austria                Germany              Italy               Japan           Netherlands         Switzerland        United Kingdom   United States
Wiring Types Allowed             No Restrictions     No Restrictions.     Stranded Wire        No Restrictions     Not Mentioned   Stranded copper     No Restrictions                     Stranded Wire
(Stranded/Solid Conductor)                           Usually stranded                                                              wires are
(Copper/ Aluminum                                    wire.                                                                         preferred
Rules for Protecting Wiring      Conduits not                             Not Strictly         Prevention of       Not Mentioned                       Not Strictly                        Flexible Cords
Insulation. Is Conduit           mandatory,                               Regulated            Electrical Shock    Yes, sunlight                       Regulated                           and Cables
Required? Are PV Array           however                                                                           resistant                                                               allowed on PV
Raceways Allowed? Sunlight       mechanical                                                                        required                                                                array where
Resistant Insulation Required?   protection is                                                                                                                                             water and
                                 preferred.                                                                                                                                                sunlight
                                 Sunlight                                                                                                                                                  resistant.
                                 Resistant
                                 required
Color Codes Allowed on PV        + Red               + Red                + Red                                                    Normally black      + Red                               + Red
array Interconnect Wiring.       - Black             - Blue               - Blue                                                                       - Blue                              - Black
                                 Preferred but       Not strictly                                                                                                                          Ground Green
                                 other colors        regulated.                                                                                                                            or Bare Wire
                                 permitted
Junction Boxes and Module        None                J-boxes              J-boxes              Standard per        Water Proof     according to IP-    J Boxes                             NEMA rated for
Interconnect Requirements                            according to IEC     According to         IEC1245                             classification      According to                        appropriate
                                                                          IEC 439-1                                                                    IEC 439-1                           locations
What are the Fusing              Not required but    Usually string                            None                Not Required    String fusing       Individual array                    Individual array
Requirements for the PV array    currently under     fuses used.                                                                   required when       strings must be                     strings must be
                                 review                                                                                            more than 2         fused.                              fused.
                                                                                                                                   strings are
                                                                                                                                   paralleled
Visible Disconnect               None                Required             Required             None, but this is   Not Required    Required            Visible                             Visible
Requirements                                         between the          between the          ENEL’s practice                     between array       disconnect                          disconnect
                                                     array and            array and                                                and inverter        required with                       required with
                                                     inverter             inverter                                                                     lockout                             lockout
                                                                                                                                                       capability when                     capability when
                                                                                                                                                       not collocated                      not collocated
                                                                                                                                                       with PV                             with PV
Lightning Protection             Not required, but   Not mandatory.       Not Mandatory.       None, but           Required        Advised for         Not Required                        Not Required
Requirements                     generally used.     If used, there are   If used, there are   ENEL’s                              larger systems at   but normally                        but normally
                                                     guidelines.          guidelines           protections                         DC side             used.                               used.




Report IEA-PVPS T5-01:1998
Utility Aspects of Grid Connected Photovoltaic Power Systems                                                      Page 17-154

Utility-Interactive (U-I) Inverters in PV Systems

Topic                             Requirement or Comment By Country
                                  Australia         Austria            Germany             Italy             Japan           Netherlands       Switzerland   United Kingdom      United States
Are U-I Inverters categorized     Yes               No                 No                  Line              Yes             No                No            Yes, Distinction    Self
                                                                                           Commutated                                                        between Line        Commutated
                                                                                                                                                             Commutated and      Line
                                                                                                                                                             Line                Commutated
                                                                                                                                                             Synchronized in     Transformerless.
                                                                                                                                                             G5911               Inverters must be
                                                                                                                                                                                 identified for use
                                                                                                                                                                                 in PV systems
Must U-I inverters be certified   Yes, but no        No                No                  Yes               Yes             No, but advised   Soon          No Overall          Yes. Listed is
                                  certification .                                                                            AC-Modules                      Certification but   the general
                                  Must conform to                                                                            must                            must conform to     certification.
                                  individual                                                                                                                 individual
                                  standards.                                                                                                                 standards
Must U-I inverters be protected   Yes                Usually yes       Yes                 Yes               Yes             Yes, according    Yes           Yes, EMC Rules      Yes
against transients                                                                                                           to standard
                                                                                                                             EMC-CE
Are dc voltages limited           Limited to         Battery voltage   To 1500 V;          NO                Yes (Based on   max. 1500Vdc =    No            Yes, ICE            Yes (600 V for
                                  associated         <120V (series     Lower values for                      insulation      IEC 364.                        Regulations.        inverters used in
                                  equipment          connection of     class III (120 V)                     requirements                                    120V dc for         residential
                                  insulation class   cells)                                                                                                  SELV                applications.
                                                                                                                                                             1500V dc for        System Voltage
                                                                                                                                                             Low Voltage         is used as the
                                                                                                                                                                                 limit.
Is dc transient protection        No, but            No, but           No, but             No. This is       Yes             No,               Yes           No, But             No
required                          recommended        recommended       recommended         ENEL’s practice                   recommended                     Recommended
Must dc circuit be grounded       No, but depends    No, Depends on    No, Depends on      No                No              No                No            No                  Yes
                                  on protection      protection        protection
                                  and earthing       measured and      measured and
                                                     earthing          earthing
Must ac circuit be grounded       Yes                Depends on        Depends on          Yes               No              No                Yes           Yes (PME            Yes
                                                     local premise     local premise                                                                         Neutral and
                                                     wiring            wiring                                                                                Earthed)




Report IEA-PVPS T5-01:1998
Utility Aspects of Grid Connected Photovoltaic Power Systems                                                         Page 17-155

Utility-Interactive Inverters in PV Systems (Continued)

Topic                            Requirement or Comment By Country
                                 Australia         Austria               Germany              Italy               Japan              Netherlands        Switzerland          United Kingdom      United States
How is dc/ac ground handled      If DC system is   If grounding          If grounding         DC system                              Bounded to         If grounding         Bonded              Bonded to
                                 floating, only PV exists, both shall    exists, both shall   floating; SC                           ground             exists, both shall                       neutral when
                                 frame bonded.     be bonded             be bonded            support structure                                         be bonded                                available.
                                 If DC earthed,                                               and ac grounded                                                                                    Bonded to
                                 bond between ac                                                                                                                                                 ground where no
                                 and dc required.                                                                                                                                                neutral
List Required Set points and     120 Vdc           No requirements       No                   Maximum             Depends on         120 Vdc            No                   120Vdc limit for
Thresholds for dc                                  specified             Requirements.        allowed by          Measuring          according to IEC   Requirements.        SELV
                                                                         Only 120V limit      inverters or        System             364                Only 120V limit
                                                                         for Class III        appliances                                                for Class III
List Required Set points and     240V +/- 6%          No requirements    No                   Vnom + 10%          5 ~ 30 ma (0.1 ~   230 -10% +6%       230/400              +10%, -6% on        Nominal + 10%
Thresholds for ac                                     specified          Requirements                             2 sec)                                +6, -10%             230V                and +6,-13% are
                                                                         Specified                                50 ~ 100 ma                                                +1, -1 frequency    used.
                                                                                                                  (0.1 sec)                                                  operating
                                                                                                                                                                             envelope
Are isolation transformers       No, but dc           Generally No.      Generally No.        Only for single-    Yes (In            No                 No                   No, but dc          No, but dc
required                         injection shall      Only for certain   Only for certain     phase connect       Principle)                                                 injection shall     injection shall
                                 not occur            protection         protection                                                                                          not occur           not occur
                                                      measures.          measures.
Are internal over/under          Yes                  Yes                Yes                  Yes                 Yes                Yes                Yes                  Yes, (Preferably    Yes
voltage/frequency features                                                                                                                                                   sealed)
allowed
Are external over/under          Yes, Unless          No or for          No                   Yes                 Yes                No                 Yes                  Yes, Electricity    No except some
volt/frequency relays required   inverter is tested   example “ENS”                                                                                                          companies           utilities may
                                 and complies                                                                                                                                discretion if can   impose such a
                                 with guidelines                                                                                                                             be combined         requirement



Comments




Report IEA-PVPS T5-01:1998
Utility Aspects of Grid Connected Photovoltaic Power Systems                                            Page 17-156

Disconnects in PV Systems

Topic                             Requirement or Comment By Country
                                  Australia         Austria           Germany         Italy          Japan               Netherlands          Switzerland      United Kingdom   United States
Where in the PV system are        Not Specified on Between the        Between the     At the dc/ac   Visible             Between array        Dc to Inverter   Not Specified,   Readily
visible disconnects required      dc. AC must       Array and the     Array and the   switch         Disconnects Not     and inverter and     Inverter to AC   but good         accessible.
                                  have labeled      Inverter          Inverter                       Required but        Inverter and                          practice         Visible
                                  disconnection                                                      disconnectors       array                                                  disconnects must
                                  point.                                                             are required for    (different for AC                                      be grouped and
                                                                                                     ac and dc           Modules)                                               identified when
                                                                                                     terminals                                                                  more than one
                                                                                                                                                                                source is
                                                                                                                                                                                available.
Is Neutral disconnected with      No center-       No                 No              N/A            No Center           No                   No               Not Specified    No
center tapped systems             tapped systems                                                     Tapped Systems
Are disconnects required on all   Not specified    Yes                Yes                            Yes                 Yes, in nearly all   Yes              Not Specified    Yes
conductors in ungrounded
systems
What disconnects are required     DC not           Load Break         Load Break                     ac side, (ELB)                           Not Specified    Not Specified    Under
in ground fault circuits          mentioned.       Capabilities       Capabilities                   Not Mentioned                                                              consideration.
                                  AC (RCD)                                                           (dc side)                                                                  Normally the
                                                                                                                                                                                array is opened
                                                                                                                                                                                or short-
                                                                                                                                                                                circuited.
Must dc disconnect be rated to    Yes              Yes                Yes             Yes            Not mentioned       Yes                  Yes              Not Specified    No. When the
break under load                                                                                     but usually rated                                                          disconnect
                                                                                                     to break load                                                              cannot be
                                                                                                                                                                                operated under
                                                                                                                                                                                load.
Are solid-state disconnects       No               No                 No              No             No (ac side)        No                   No               No, (AC side)    No
allowed                                                                                              Not Mentioned
                                                                                                     (dc side)
Are array disable switches or     No               Yes                No              Yes            Not Mentioned       No                   No               Not Specified,   No, but good
relays required for fire safety                                                                                                                                but good         engineering
                                                                                                                                                               practice         practice.




Report IEA-PVPS T5-01:1998
Utility Aspects of Grid Connected Photovoltaic Power Systems                                               Page 17-157

Thresholds, Protective Devices and Circuits Required in PV Systems

Topic                           Requirement or Comment By Country
                                Australia         Austria           Germany         Italy              Japan                Netherlands        Switzerland     United Kingdom   United States
DC GFI Requirements             Not Specified                       Not Regulated   Any                                                        Not Regulated   Not Specified    30 ma
                                                                                    Requirements
AC GFI Requirements             30 ma                               Not Regulated   Yes                                                        Not Regulated   30 ma domestic   5 ma
Max DC Voltage                  120V, 1500V                         120V, 1500V     LV limit of 600    750V for low         120,1500 Vdc       120V, 1500V     120V, 1500V      600 for
                                                                                    Vdc                voltage class                                                            residential
Max AC Voltage                  415 V, 3-Phase     Not Regulated    Not Regulated   LV limit of 1000   600 V for low        230/415            Open            415 V, 3-Phase   600 for
                                                                                    Vdc                voltage class                                                            residential
Max Ground Resistance           Not Specified      Not Regulated    Not Regulated   Any                100 ohms (in         No regulated       According to    Designed to      Variable, but
Requirements                                                                                           case of installing                      IEC1216         meet ICE         often less than 3
                                                                                                       ELB, 500 ohms                                           disconnection    ohms.
                                                                                                                                                               times
Islanding Detect Requirements   Yes, Passive and   Required         Can Replace                        Required             Yes,               Not Required    Required by      Under
                                Active Detect                       external                                                                                   9591             discussion.
                                                                    disconnect                                                                                                  Generally
                                                                                                                                                                                required by
                                                                                                                                                                                utilities
   Passive Allowed or           U/O Voltage                                         Min/Max            Required             Only voltage and   Required        Min/Max          Voltage and/or
Required                        U/O Frequency                                       Voltage and                             frequency                          Voltage and      frequency
                                                                                    frequency                               window                             Frequency
                                                                                                                            Negative
                                                                                                                            frequency shift
                                                                                                                            is advised
   Active Allowed or            At least two       3-phase UV       3-phase UV                         Required             No                 Not Required    Loss of Mains    Non at this time
Required                        active methods     relay or ENS     relay or ENS                                                                               EG ROCOF
                                required.
                                Method not
                                specified.




Report IEA-PVPS T5-01:1998

								
To top