UTILITY ASPECTS OF GRID CONNECTED PHOTOVOLTAIC POWER SYSTEMS

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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 ET, Arnhem, The Netherlands s.a.m.verhoeven@kema.nl To obtain additional copies of this report or information on other IEA-PVPS publications, contact the IEA website:

2 Utility Aspects of Grid Connected Photovoltaic Power Systems Page 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 and ground fault detection of PV-systems Lightning induced overvoltages EMI of inverters Reclosing External disconnect Isolation transformer and DC-injection Islanding of inverters in a part of the network 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.

3 Utility Aspects of Grid Connected Photovoltaic Power Systems Page ANNEX B SYSTEM GROUNDING SUMMARY The 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 for grounding of PV systems in eight participating IEA countries. PV Array (Conductive Frame) PV Source Circuit Batteries Associated with PV Array Conductive Battery Support Structure Inverter with Conductive case, Requirement Inverter Active Circuit Conductors Are Center-Tapped DC Systems Allowed Are High Resistance s Allowed t if fuse in both + and earth connections Recommended for lightning, Prohibited for certain classes earthing and isolation transformer ne Recommended for Lightning. Prohibited for Certain classes DE- VDE0100 Part 712 Draft earthing and isolation transformer t ne Case ) class class Neutral ed system earthing & (MEN System configuration isolation transformer CEI-ETD Requirement for ne Case Active Circuit - Requirement Requirement ne Case - Active Circuit t required, normal practice is to have floating DC circuit t Metal case must be grounded. t required, normal practice is floating DC t t t (IEE Regulations BS7430) te: PME Earth Should not be taken outside of Building t t t t discussed t Decided t Generally, (t mentioned) ( In Principle), Earth leakage detection required NEC for >50V is where non-qualified personnel have access for >50V. Case - Active circuit for >50V

4 Utility Aspects of Grid Connected Photovoltaic Power Systems Page System Summary (Continued) DC/AC Intertie (Bond) Are Fault Detectors on DC Circuits Are Fault Detectors on AC Circuits Are DC-Side Transient Suppressers Are AC -Side Transient Suppressers Is Charge Controller/System Controller t t Decided t specified t t earthing system but varies from isolation to bond., but generally used on large systems, but generally used on MV systems, for DCvoltage > 120 t, for systems mounted on dwellings t Mandatory, Requirement is for Disconnection Times to be Met t, Class C, but recommended, but used by ENEL Recommended t General Practice to Include, but generally used t, but usually used t Mentioned t Mentioned t mentioned t t with system. Usually exceptions for current limited systems and for systems >50V. Comments

5 Utility Aspects of Grid Connected Photovoltaic Power Systems Page 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 for the PV array installation. PV Source Circuit Metal Frame /Bonding Frameless or n-conductor frame Module grounding t Regulated earthing system generally recommended. Prohibited with certain t regulated. Class II suggested Blocking Diode ne. May be omitted with Class II modules Bypass Diode General Practice According to Manufacturer specifications. Allowable Open Circuit Voltage for Array Wire Insulation Types Allowed t Must pass compliance tests for UV, heat etc. t discussed. Module Specification (usually 600V) t, but cables must withstand expected ambient and outdoor conditions Earthing System generally recommended. Prohibited with certain t Regulated. Class II suggested. May be Omitted with Class II modules. According to Manufacturer Specs 1500V. 120 V for Class III Systems.(Vdc 0-100) t, but cables must withstand expected ambient conditions grounding, Using standardized components grounding grounding grounding may be a resistance ground ne t Mentioned t regulated ne Metal structure must be grounded. ne, but practiced by ENEL General Practice 600V for LV 50V for passive safety Certified (Possible to Remove) (Possible to Remove) 750 V (JIS deals only with under 750V dc Voltage) IV (Poly-vinyl) CT (Rubber) CV-CE (Polyethylene) ne ne t. ne Max 1500 Vdc according to IEC 364 Cables must be suitable for application. Double insulation General Practice. (Module supplier requirement) Product Specification t Specifically, but cables must withstand expected ambient conditions t 600 Volts for One and Twofamily dwellings. other systems limited to 1000V listing limit. Types USE, UF, SE permitted. Where exposed to sunlight, USE, UF, or others listed & marked sunlight resistant

6 Utility Aspects of Grid Connected Photovoltaic Power Systems Page PV Array (Continued) Wiring Types Allowed (Stranded/Solid Conductor) (Copper/ Aluminum Rules for Protecting Wiring Insulation. Is Conduit? Are PV Array Raceways Allowed? Sunlight Resistant Insulation? Color Codes Allowed on PV array Interconnect Wiring. Junction Boxes and Module Interconnect What are the Fusing for the PV array Visible Disconnect Lightning Protection Restrictions Conduits not mandatory, however mechanical is preferred. Sunlight Resistant required + Red - Black Preferred but other colors permitted ne t required but currently under review ne t required, but generally used. Restrictions. Usually stranded wire. + Red - Blue t strictly regulated. J-boxes according to IEC Usually string fuses used. between the array and inverter t mandatory. If used, there are guidelines. Stranded Wire Restrictions t Mentioned Stranded copper wires are preferred t Strictly Regulated + Red - Blue J-boxes According to IEC between the array and inverter t Mandatory. If used, there are guidelines Prevention of Electrical Shock Standard per IEC1245 t Mentioned, sunlight resistant required Water Proof rmally black according to IPclassification ne t String fusing required when more than 2 strings are paralleled ne, but this is ENEL s practice ne, but ENEL s s t between array and inverter Advised for larger systems at DC side Restrictions t Strictly Regulated + Red - Blue J Boxes According to IEC Individual array strings must be fused. Visible disconnect required with lockout capability when not collocated with PV t but normally used. Stranded Wire Flexible Cords and Cables allowed on PV array where water and sunlight resistant. + Red - Black Green or Bare Wire NEMA rated for appropriate locations Individual array strings must be fused. Visible disconnect required with lockout capability when not collocated with PV t but normally used.

7 Utility Aspects of Grid Connected Photovoltaic Power Systems Page Utility-Interactive (U-I) Inverters in PV Systems Are U-I Inverters categorized Line Commutated Must U-I inverters be certified Must U-I inverters be protected against transients Are dc voltages limited, but no certification. Must conform to individual standards., but advised AC-Modules must Usually yes, according to standard EMC-CE Limited to associated equipment insulation class Battery voltage <120V (series connection of cells) Is dc transient required, but recommended, but recommended Must dc circuit be grounded, but depends, on and earthing measured and earthing Must ac circuit be grounded local premise wiring To 1500 V; Lower values for class III (120 V), but recommended, measured and earthing local premise wiring NO, Distinction between Line Commutated and Line Synchronized in G5911 (Based on insulation max. 1500Vdc = IEC 364. Soon Overall Certification but must conform to individual standards, EMC Rules, ICE Regulations. 120V dc for SELV 1500V dc for Low Voltage. This is,, But ENEL s practice recommended Recommended (PME Neutral and Earthed) Self Commutated Line Commutated Transformerless. Inverters must be identified for use in PV systems. Listed is the general certification. (600 V for inverters used in residential applications. System Voltage is used as the limit.

8 Utility Aspects of Grid Connected Photovoltaic Power Systems Page Utility-Interactive Inverters in PV Systems (Continued) How is dc/ac ground handled List Set points and Thresholds for dc List Set points and Thresholds for ac Are isolation transformers required Are internal over/under voltage/frequency features allowed Are external over/under volt/frequency relays required If DC system is floating, only PV frame bonded. If DC earthed, bond between ac and dc required. If grounding exists, both shall be bonded 120 Vdc specified 240V +/- 6%, but dc injection shall not occur specified Generally. Only for certain measures. If grounding exists, both shall be bonded. Only 120V limit for Class III Generally. Only for certain measures. DC system floating; SC support structure and ac grounded Maximum allowed by inverters or appliances Measuring System Vnom + 10% 5 ~ 30 ma (0.1 ~ 2 sec) 50 ~ 100 ma (0.1 sec) Only for singlephase connect (In Principle) Bounded to ground 120 Vdc according to IEC 364 If grounding exists, both shall be bonded. Only 120V limit for Class III % +6% 230/400 +6, -10% Bonded 120Vdc limit for SELV +10%, -6% on 230V +1, -1 frequency operating envelope, but dc injection shall not occur, (Preferably sealed), Unless inverter is tested and complies with guidelines or for example ENS, Electricity companies discretion if can be combined Bonded to neutral when available. Bonded to ground where no neutral minal + 10% and +6,-13% are used., but dc injection shall not occur except some utilities may impose such a requirement Comments

9 Utility Aspects of Grid Connected Photovoltaic Power Systems Page Disconnects in PV Systems Where in the PV system are visible disconnects required Is Neutral disconnected with center tapped systems Are disconnects required on all conductors in ungrounded systems What disconnects are required in ground fault circuits Must dc disconnect be rated to break under load Are solid-state disconnects allowed Are array disable switches or relays required for fire safety t on dc. AC must have labeled disconnection point. Between the Array and the Inverter Between the Array and the Inverter At the dc/ac switch Visible Disconnects t but disconnectors are required for ac and dc terminals Between array and inverter and Inverter and array (different for AC Modules) Dc to Inverter Inverter to AC t, but good practice centertapped N/A Center t systems Tapped Systems t specified, in nearly all t DC not mentioned. AC (RCD) Load Break Capabilities Load Break Capabilities ac side, (ELB) t Mentioned (dc side) t mentioned but usually rated to break load (ac side) t Mentioned (dc side) Readily accessible. Visible disconnects must be grouped and identified when more than one source is available. t t Under consideration. rmally the array is opened or shortcircuited. t. When the disconnect cannot be operated under load., (AC side) t Mentioned t, but good practice, but good engineering practice.

10 Utility Aspects of Grid Connected Photovoltaic Power Systems Page Thresholds, Protective Devices and Circuits in PV Systems DC GFI t t Regulated Any t Regulated t 30 ma AC GFI 30 ma t Regulated t Regulated 30 ma domestic 5 ma Max DC Voltage 120V, 1500V 120V, 1500V LV limit of 600 Vdc 750V for low voltage class 120,1500 Vdc 120V, 1500V 120V, 1500V 600 for residential Max AC Voltage 415 V, 3-Phase t Regulated t Regulated LV limit of 1000 Vdc 600 V for low voltage class 230/415 Open 415 V, 3-Phase 600 for residential Max Resistance regulated According to IEC1216 Islanding Detect Passive Allowed or Active Allowed or t t Regulated t Regulated Any 100 ohms (in case of installing ELB, 500 ohms, Passive and Active Detect U/O Voltage U/O Frequency At least two active methods required. Method not specified. 3-phase UV relay or ENS Can Replace external disconnect 3-phase UV relay or ENS Min/Max Voltage and frequency Designed to meet ICE disconnection times, t by 9591 Only voltage and frequency window Negative frequency shift is advised Min/Max Voltage and Frequency t Loss of Mains EG ROCOF Variable, but often less than 3 ohms. Under discussion. Generally required by utilities Voltage and/or frequency n at this time