Utility Interconnection - Energy Consultants Group · 2018. 3. 1. · IEEE 1547 Standard for...

2012 Jim Dunlop Solar

Chapter 12

Utility Interconnection

Codes and Standards ● Utility Considerations ● Supply and Load Side Connections ●

Interconnection Agreements

Presenter

Presentation Notes

Nearly all electric utilities allow the interconnection of customer-owned and operated PV systems to their distribution systems. The technical and safety requirements for interconnected power sources are addressed in national codes and standards, while the specific procedures and policies vary among local utilities. References: Photovoltaic Systems, Chap. 12 Connecting to the Grid – A Guide to PV Interconnection Issues, Interstate Renewable Energy Council: www.irecusa.org Database of State Incentives for Renewable Energy: www.dsireusa.org

2012 Jim Dunlop Solar Utility Interconnection: 12 - 2

Overview

Identifying the codes and standards for interactive PV systems and equipment.

Classifying types of utility-interactive photovoltaic systems.

Understanding the requirements for supply side and load side interconnections.

Identifying the terms and conditions for utility interconnection agreements.

Distinguishing between net metering and other types of utility revenue metering.

Presenter

Presentation Notes

Reference: Photovoltaic Systems, p. 327


Interconnection

Interconnection refers to the

technical and procedural matters associated with operating interactive PV systems and other distributed generation sources in parallel with the electric utility system.

Presenter

Presentation Notes

Interconnection is the process of connecting power generation sources to the electric utility network. Reference: Photovoltaic Systems, p. 327


Interconnection Issues

Technical issues include:

Protections for the public and utility and other workers; power quality and

impact on the utility system; installation codes.

Procedural and administrative issues include: Utility and government policies and laws; interconnection agreements;

tariffs, rates and fees.

Presenter

Presentation Notes

Technical interconnection issues include safety, power quality, and impacts on the utility system, and are addressed in national codes and standards. Interconnection procedures are based on state and utility policies, and include the application process and schedule, customer agreements, and permitting and inspection. Contractual aspects of interconnection policies include fees, metering requirements, billing arrangements, and size restrictions on the distributed generator.


Utility Concerns with Distributed Generation

Electric utility concerns about customer-owned distributed

generation include: Generation operating on their system that they do not maintain or control. Protection of electrical system equipment. Reliability of equipment, and impacts on the sizing and operation of utility

services. Power quality impacts on the utility system and other customers. Impacts during utility outages and disturbances (anti-islanding protection). Liability and safety of utility personnel and the public.

Presenter

Presentation Notes

Electric utilities have concerns about PV systems and other forms of distributed generation operating on their systems that they do not own, operate, maintain or control. The foremost concern is the safety of utility personnel and the public, and the associated liabilities. Additionally, utilities are concerned about the protection, reliability and impacts on the sizing and operation of utility distribution equipment and services to other customers. These concerns are addressed by standards for equipment and installations, including product certification and listing, and electrical codes that help ensure the safe and reliable interconnection of PV systems to the utility grid. Reference: Photovoltaic Systems, p. 342-347


History of Distributed Generation and PURPA

The Public Utility Regulatory Policy Act (PURPA, 1978) is a

federal law that created the first markets for independent power producers. Requires electric utilities to purchase energy generated from independent

power producers, called Qualifying Facilities (QF).

Energy prices are to be based on “avoided costs”, equivalent to the utility’s cost of producing energy or wholesale rate.

QF rules may apply to privately-owned utility-scale PV systems larger than local net metering rules allow.

Presenter

Presentation Notes

The Public Utilities Regulatory Policy Act (PURPA) of 1978 was the first federal legislation affecting the interconnection of distributed generation resources. This law was intended to decrease U.S. dependence on foreign oil by encouraging the use of renewable energy and cogeneration resources. PURPA established the first opportunities for non-utility power producers by eliminating barriers that previously hindered their entry into a market controlled by public utilities. PURPA requires electric utilities to establish reasonable rates and to purchase energy from independent power producers, and to establish the technical and procedural requirements for their interconnection to the utility system, subject to regulatory approval. A qualifying facility (QF) is non-utility power generator, meeting the technical and procedural requirements for interconnection to the utility system. PURPA mandates that utilities purchase power from QFs at the utility's avoided cost. Avoided costs are the costs that a utility incurs to generate or purchase power, synonymous with the wholesale value of electricity. PURPA requires regulated utilities to file their QF tariffs with the Federal Energy Regulatory Commission (FERC) for approval. Reference: Photovoltaic Systems, p. 342-344


Interconnection Codes and Standards

IEEE 1547: Standard for Distributed Resources Interconnected

with Electric Power Systems Establishes technical and operational requirements.

UL 1741: Inverters, Converters, Controllers and Interconnection

System Equipment for Use With Distributed Energy Resources Defines equipment test procedures and product listing requirements.

National Electrical Code - NFPA 70

Prescribes installation requirements. • Article 690: Solar Photovoltaic Systems • Article 705: Interconnected Electric Power Production Sources

Presenter

Presentation Notes

The technical requirements for PV system interconnections are established through national codes and standards developed by the Institute of Electrical and Electronics Engineers (IEEE), Underwriters Laboratory (UL) and the National Fire Protection Association (NFPA). These organizations work collectively to ensure electrical equipment and installations are inherently safe through the combination of standards, equipment testing and certification, and enforceable codes. Reference: Photovoltaic Systems, p. 332-334


IEEE 1547

IEEE 1547 Standard for Interconnection of Distributed Resources

with Electrical Power Systems: Covers technical requirements for the interconnection of PV systems and

other distributed generators. Addresses personnel safety, equipment protection, power quality and

islanding protection.

Does not address procedural or administrative details of interconnection agreements.

Presenter

Presentation Notes

IEEE 1547 Standard for Interconnection of Distributed Resources with Electrical Power Systems establishes the technical requirements for interconnecting all types of distributed generation equipment, including photovoltaics, fuel cells, wind generators, reciprocating engines, microturbines, and larger combustion turbines with the electrical power system. It also establishes requirements for testing, performance, maintenance and safety of the interconnection, as well as response to abnormal events, anti-islanding protection and power quality. The focus of IEEE 1547 is on distributed resources with capacity less than 10 MVA, and interconnected to the electrical utility system at primary or secondary distribution voltages. The standard provides universal requirements to help ensure a safe and technically sound interconnection. It does not address limitations or impacts on the utility system in terms of energy supply, nor does it deal with procedural or contractual issues associated with the interconnection. References: Photovoltaic Systems, p. 332-334 http://grouper.ieee.org/groups/scc21/


IEEE 1547 Series of Standards

IEEE 1547 consists of the main

standard, in addition to a series eight other standards and guidelines dealing with various aspects of interconnecting distributed power sources.

IEEE 1547 is the basis for UL 1741 listing of interactive PV inverters.

IEEE SCC21

Presenter

Presentation Notes

IEEE-1547.1 Standard for Conformance Test Procedure for Interconnecting Distributed Resources with Electrical Power Systems IEEE 1547.2 Application Guide for IEEE Standard 1547 for Interconnection of Distributed Resources with Electrical Power Systems IEEE 1547.3 Guide for Monitoring, Information Exchange and Control of Distributed Resources Interconnected with Electrical Power Systems IEEE P1547.4 Draft Guide for Design, Operation and Integration of Distributed Resource Island Systems with Electrical Power Systems IEEE P1547.5 Draft Technical Guidelines for Interconnection of Electric Power Sources Greater than 10MVA to the Power Transmission Grid IEEE P1547.6 Draft Recommended Practice for Interconnecting Distributed Resources with Electric Power Systems Distribution Secondary Networks IEEE P1547.7 Draft Guide to Conducting Distribution Impact Studies for Distributed Resource Interconnection IEEE P1547.8 Draft Recommended Practice for Establishing Methods and Procedures that Provide Supplemental Support for Implementation Strategies for Expanded Use of IEEE Standard 1547 References: Photovoltaic Systems, p. 332-334 http://grouper.ieee.org/groups/scc21/


Islanding

Islanding is a condition where part of a utility system containing

both load and generation is isolated from the remainder of the utility system but remains energized.

Islanding of PV systems and other distributed generation is an undesirable condition, and presents two basic concerns: Lack of voltage and frequency control Safety for electric utility workers

Presenter

Presentation Notes

Islanding is a condition where part of a utility system containing both load and generation is isolated from the remainder of the utility system but remains energized. Islanding of PV systems and other distributed generation is an undesirable condition, and presents two basic problems for electric utilities in terms of safety and operation of the utility system. First, utilities have no control over the voltage and frequency with distributed generation islanding. If an island condition develops with a distributed generator when the utility becomes de-energized, damage to the distributed generator or utility equipment may result if the island is allowed to be reconnected to the grid. Islanding can also interfere with the utility’s normal procedures for bringing their system back into service following an outage, primarily because the islanded electrical system is no longer in phase with the utility system. Second and more importantly, the creation of an island presents a safety hazard for utility linemen working to restore power after an outage. While utilities are able to ensure their equipment is isolated properly, they are less confident about customer-owned generation that they do not control. Reference: Photovoltaic Systems, p. 334


Anti-Islanding Protection

IEEE 1547 requires PV systems and other distributed generation

sources to be able to detect when an island is forming and stop supplying power to the grid until the utility system is re-energized.

Listed, interactive PV inverters have integral anti-islanding protection. Inverters must disconnect their output to the grid within two seconds when

an islanding condition is detected. Inverters shall remain disconnected until the utility has been re-energized

to acceptable voltage and frequency limits for a period of five minutes.

Presenter

Presentation Notes

IEEE 1547 requires PV systems and other distributed generation sources to be able to detect when an island is forming and stop supplying power to the grid until the utility system returns to its normal operating limits. Interactive PV inverters must have a minimum of two detection methods for both passive and active islanding (total of four). This is accomplished through anti-islanding circuitry internal to inverters, and evaluated under UL 1741 as part of the equipment listing. Inverters meeting this standard are often referred to as “non-islanding” inverters – in part distinguishing them from stand-alone inverters. Conventional rotating generators use external over/under voltage and frequency relaying equipment to prevent islanding. Reference: Photovoltaic Systems, p. 334


Monitoring and Isolation

IEEE 1547 requires distributed generators with an aggregate

capacity of 250 kVA or more to have provisions for monitoring interconnection status, real power, reactive power and voltage at the point of connection.

When required by utilities, a readily accessible, lockable, visible-break isolation device (disconnecting means) shall be located between the distributed generator and utility grid.

Presenter

Presentation Notes

IEEE 1547 requires monitoring for distributed generators 250 KVA and larger, and specifies a readily accessible, lockable, visible-break disconnecting means subject to local utility policies.


Voltage

IEEE 1547 required the following voltage regulation standards for distributed generators:

The DG system must not cause the service voltage to go outside the requirements of ANSI C84.1, Range A. The DG system must not cause the service voltage to fluctuate more than ±5% when interconnecting.

The DG system must de-energize its output within a specified time under abnormal voltage conditions: < 50% of nominal voltage (V), 0.16 sec (~10 cycles) 50% to 88% of nominal voltage, 2 sec (120 cycles) 110% to 120% of nominal voltage, 1 sec (60 cycles) > 120% of nominal voltage, 0.16 sec

The service voltage must be within ANSI C84.1, Range B for 5 minutes

before reconnection.

Presenter

Presentation Notes



Frequency

IEEE 1547 requires frequency to be maintained within the

following limits:

For distributed generators under 30 kW, the DG system must de-energize its output within a 0.16 seconds if the frequency falls outside the range of 59.3 to 60.5 Hz. 57 to 60.5 Hz for DG systems larger than 30 kW

Frequency must remain in the range of 59.3 to 60.5 Hz for 5

minutes prior to reconnection.

Presenter

Presentation Notes



Power Quality

IEEE 1547 also requires distributed generators to conform to

certain power quality standards: DC current injection must be less than 0.5%. Current harmonics are limited to a specified percentage depending on the

harmonic order. Total demand distortion (TDD) for current must be less than 5%.

Presenter

Presentation Notes

Power quality is among the principal concerns for electric utilities, especially for distributed generation equipment interconnected to their system. Power quality addresses a broad range of utility waveform properties, including voltage, frequency, harmonic distortion, power factor, DC injection, voltage flicker and noise on the utility system. Reference: Photovoltaic Systems, p. 334


UL 1741

UL 1741 Inverters, Converters, Controllers and Interconnection

System Equipment for Use With Distributed Energy Resources: Covers inverters, converters, charge controllers, combiner boxes and AC

modules for use in stand-alone or utility-interactive power systems.

Products covered by these requirements are intended to be installed in accordance with the National Electrical Code, NFPA 70.

Presenter

Presentation Notes

UL 1741 Inverters, Converters, Controllers and Interconnection System Equipment for Use with Distributed Energy Resources addresses requirements for all types of distributed generation equipment, including inverters, charge controllers and combiner boxes used in PV systems, as well as equipment used for the interconnection of wind turbines, fuel cells, microturbines and engine-generators. This standard covers requirements for the utility interface, and is intended to supplement and be used in conjunction with IEEE 1547. The products covered by the UL 1741 listing are intended to be installed in accordance with the National Electrical Code, NFPA 70. Reference: Photovoltaic Systems, p. 334


Characteristics of Distributed Generators

Rotating Generators:

A voltage source Can deliver high fault current Can act as a load Synchronization and protection uses

separate equipment

Electronic Inverters:

A current source Limited fault current Can not act as a load Synchronization and protection

features are integral to inverters

Mechanical rotating generators and electronic inverters have different

characteristics that affect their interconnection to the grid.

Presenter

Presentation Notes

Distributed generation technologies can be classified as using either with rotating generators or static electronic inverters. The type of prime mover has important distinctions when considering the requirements for interconnecting these systems to the electric utility grid. Reference: Photovoltaic Systems, p. 328-330


Synchronizing

Synchronizing is the process of connecting a generator to an energized electrical system, and involves: Phase sequencing Speed and frequency control Voltage control Phase matching

Modern electronic inverters

perform all synchronizing functions internal to the inverter circuitry.

Presenter

Presentation Notes

Synchronizing is the process of connecting a generator to an energized electrical system. Synchronizing is also called paralleling a generator, or bringing it on-line. The prerequisites for synchronizing a rotating electrical generator with the grid are extremely critical, and involves four important steps before the interconnection can be made. 1. The phase sequence of the generator must be the same as other generators already operating on the electrical system. This means it must be rotating in the same direction. A phase-sequence indicator is used to determine in what order the phases reach their maximum voltage. 2. The synchronizing generator must be operating at the same frequency as other generators on the system. Frequency is controlled by the rotating speed of the generator, and based on the number of field poles. 3. The voltages of the generator and grid at the point of connection must be the same. Voltage is controlled by varying the generator field current and magnet strength. 4. The generator and grid voltages must be in phase.


Types of Interactive PV Systems

Interactive Systems without Energy Storage

Operate interconnected (in parallel) with the utility grid.

Bi-Modal Interactive Systems with Energy Storage May operate in either utility-interactive or stand-alone mode, but not

simultaneously.

Presenter

Presentation Notes

Interactive PV systems operate in parallel with and are interconnected to the electric utility grid. The primary component in interactive PV systems is the inverter, which directly interfaces between the PV array and electric utility network, converts DC power from a PV array to AC power, synchronizes with the grid and provides protective functions. Reference: Photovoltaic Systems, p. 329-331


Utility-Interactive PV System

Load Center

PV Array Inverter

AC Loads

Electric Utility

Presenter

Presentation Notes

The most common type interactive PV system is one that does not use energy storage. These systems make a bi-directional interface at the point of utility interconnection, typically at a site distribution panel or electrical service entrance. Consequently, power can be exchanged in a bi-directional manner between an interactive system and the utility at the point of interconnection, making it a supplementary generation source operating on the electric utility network. The interconnection allows the AC power produced by the PV system to either supply on-site electrical loads or to back-feed the grid when the PV system output is greater than the site load demand. At night and during other periods when the electrical loads are greater than the PV system output, the balance of power required by the loads is received from the electric utility.


Utility-Interactive PV System with Energy Storage

Inverter/ Charger

Critical Load Sub Panel

Backup AC Loads

Main Panel

Primary AC Loads

Electric Utility

Bypass circuit

Battery PV Array

AC Out AC In

DC In/out

Charge Control

Presenter

Presentation Notes

Bimodal systems are utility-interactive systems that use battery storage. They can operate in either interactive or stand-alone mode, but not simultaneously. Bi-modal PV systems operate in a similar manner to uninterruptible power supplies, and have many similar components. Under normal circumstances when the grid is energized, they inverter acts as a diversionary charge controller and limits battery voltage and state-of charge. When the primary power source is lost, a transfer switch internal to the inverter opens the connection with the utility, and the inverter operates dedicated loads that have been disconnected from the grid. An external bypass switch is usually provided to allows the system to be taken off-line for service or maintenance, while not interrupting the operation of electrical loads. Reference: Photovoltaic Systems, p. 329-331


Installation Requirements

The installation requirements for PV systems and other

interconnected distributed generators are covered by the National Electrical Code (NEC), NFPA 70. Article 690, Solar Photovoltaic Systems Article 705, Interconnected Electric Power Production Sources

The installation and connection of distributed generators in

parallel with the electric utility system must be performed by qualified persons [705.6].

Presenter

Presentation Notes

NEC Article 690 Part VII addresses the connection of PV systems to other power sources, and applies to all interactive PV systems connected to the utility grid. For the 2011 NEC, many of the common interconnection requirements applicable to all distributed generators, including PV systems, fuel cells and wind turbines were moved to Article 705. See NEC Article 100 for definition of qualified persons [705.6]. References: Photovoltaic Systems, p. 334-340 NEC Articles 690, 705


Point of Connection

The point of connection, or point of common coupling, is the

point where a distributed generator interfaces with the electric utility system. The point of connection may be located on the load or supply side of a

facility service disconnecting means.

Special markings and labels are required at the point of connection.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 334-340 NEC Articles 690, 705


Point of Connection Markings

Markings are required for

interconnected PV power sources at the disconnecting means, and must indicate the following: A PV power source Nominal AC operating voltage Maximum AC current

Presenter

Presentation Notes

Reference: NEC 690.54


Point of Connection Markings

Facilities supplied by both utility services and PV systems must have a

permanent plaque or directory showing the location of the service disconnecting means and the PV system disconnecting means, if not co-located.

Presenter

Presentation Notes

A directory of power sources and location of disconnecting means are required for safety and access to emergency responders. References: NEC 690.56, 705.10


Identified Interactive Equipment

Inverters and AC modules used

in utility-interactive PV systems must be listed and identified for interactive operation, and special markings are required on the product listing label.

Presenter

Presentation Notes

All inverters and AC modules that are specifically intended to be used in utility-interactive PV systems must be listed and identified for interactive operations, and this information must be marked on the product label. Battery-based inverters intended only for stand-alone off-grid applications do not have these special identification markings, and may not be used for grid-connected applications. However, all inverters used in PV systems must be listed to the UL 1741 standard, whether they are used for stand-alone or interactive systems. References: NEC 690.60, 705.4


Loss of Interactive Power

To prevent islanding, interactive inverters and AC modules must

disconnect their output from the grid upon loss of grid voltage. Prevents energizing of otherwise de-energized system conductors and is

intended to prevent electric shock. Addressed in the IEEE1547 standard and UL1741 inverter listing. Can be demonstrated during system commissioning. This feature is integral to all listed utility-interactive inverters.

A normally interactive PV system is permitted to operate as a

stand-alone system to supply loads that have been disconnected from the utility grid. Special battery-based interactive inverters are required.

Presenter

Presentation Notes

Inverters or AC modules must be capable of de-energizing their output to the utility grid when the grid voltage is lost. This concern relates to islanding, and requires the inverter to automatically disconnect from the grid to prevent from potentially backfeeding an un-energized grid and creating a safety hazard. This grid output must also remain de-energized until grid voltage is restored. These functions are accomplished by internal inverter circuitry, and can also be demonstrated with equipment in the field. Other forms of distributed generation may require external equipment to provide this protection. A normally interactive solar photovoltaic system is also permitted to operate as a stand-alone system to supply loads that have been disconnected from electrical production and distribution network sources. This requires a special battery-based inverter intended for this purpose, with a separate dedicated load subpanel. References: NEC 690.6, 705.40


Ampacity of Neutral Conductor

Single-phase, 2-wire inverters connected to the neutral conductor

and one ungrounded conductor of a 3-wire system or of a 3-phase, 4-wire, Wye-connected system can potentially overload the neutral conductor.

The maximum load connected between the neutral conductor and any one ungrounded conductor plus the inverter output rating must not exceed the ampacity of the neutral conductor.

Most single-phase interactive inverters have two-wire output with no neutral connection and avoid this concern.

Presenter

Presentation Notes

Most single-phase inverters have two ungrounded conductors, operating at 208/240 V output, and avoid this concern. Some single-phase PV inverters have two-wire output, one neutral and one hot. If these inverters are connected to the neutral and one ungrounded conductor of a 3-wire split-phase system, or of a 3-phase, 4-wire Wye-connected system, the potential exists for overloading the neutral conductor. The sum of the maximum load between the neutral and ungrounded conductor and the inverter power rating must not exceed the ampacity of the neutral conductor. Many single-phase inverters have two-wire output with no neutral connection, which avoids this problem. References: Photovoltaic Systems, p. 335 NEC 690.62 (2008), 705.95 (2011)


Unbalanced Interconnections

Single-phase inverters must not cause unbalanced phase

voltages when connected to three-phase power systems. Solutions are to use three smaller single-phase inverters connected to

each phase, or a larger three-phase inverter.

Three-phase inverters must automatically de-energize all phases upon loss of service voltage in one or more phases.

Presenter

Presentation Notes

Precautions must be taken to ensure that larger single-phase inverters connected to 3-phase power systems do not result in unbalanced phase voltages. Solutions are to use three smaller single-phase inverters connected to each phase, or a larger single 3-phase inverter. Three-phase inverters must have all phases automatically de-energized upon loss of, or unbalanced, voltage in one or more phases unless the interconnected system is designed so that significant unbalanced voltages will not result. Three-phase inverters are common above 15 to 30 kW. References: Photovoltaic Systems, p. 335 NEC 690.63 (2008), 705.100 (2011)


Point of Interconnection

Interactive inverters may

be connected to either the load side or the supply side of the service disconnecting means.

Distribution Equipment

To Utility

To Branch Circuits

Service Disconnect

Supply Side

Load Side

Presenter

Presentation Notes

The output of interactive PV inverters may be connected to either the supply side or load side of the service disconnecting means. For many smaller systems, the point of connection is usually made on the load side of the service disconnect at any distribution equipment on the premises, usually at a panelboard. When the requirements for load side connection become impractical, interactive PV systems and other interconnected power sources may be connected to the supply side of the service disconnecting means. In cases of very large PV installations, existing service conductor ampacity or distribution transformers may not be sufficient and separate services may be installed. Power flow can occur in both directions at the point of connection, and the interface equipment and any metering must be sized and rated for the operating conditions. Systems larger than 100 kW at other points on a premises, provided qualified persons operate and maintain the systems, and that appropriate safeguards, procedures and documentation are in place. References: Photovoltaic Systems, p. 336-340 NEC 690.64, 705.12, 230.82(6)


Supply Side Connections

Supply side interconnections are made on utility side of the

service disconnecting means.

Requirements are similar to installing a new service, and often used where the requirements for load side connections can not be met.

The sum of overcurrent devices supplying the service must not be greater than the service rating.

Presenter

Presentation Notes

Interactive PV systems are permitted to connected to the supply side of the service disconnecting means. These requirements are similar to installing another service entrance, which involves tapping service conductors or installing new service equipment. Supply side interconnections are often required for larger installations where existing services and/or main distribution panels do not have sufficient capacity or can not meet the requirements for load side interconnections. The sum of the ratings for overcurrent devices supplying a service must not exceed the service ratings. References: Photovoltaic Systems, p. 339-340 NEC 690.64, 705.12(A), 230.86(6)


Supply Side Connection


To Utility

To Branch Circuits

Service Disconnect

Interactive Inverter

Service Rated Fused Disconnect

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 339-340 NEC 690.64, 705.12, 230.82(6)


Supply Side Connections

The following requirements apply to supply side connections:

The disconnect and overcurrent device must be rated as service equipment, have a minimum rating of at least 60 amps, and have an interrupt rating sufficient for the maximum available fault current. Must be grouped with main service disconnect, and no more than six (6)

service disconnects are allowed. A service-rated fused disconnect or circuit breaker meets the

requirements. Disconnect may also satisfy a utility’s interconnection requirements when

an accessible, visible-break, lockable safety switch is used.

Presenter

Presentation Notes

Supply side connections must have appropriate disconnecting means and overcurrent protection. The connection can be made by tapping the service conductors at the main distribution panel prior to the existing service disconnect, or it may be made on the load side of the meter socket if the terminals permit. Additional pull boxes may be installed to provide sufficient room for the tap. Service equipment for larger commercial facilities often has busbars with provisions for connecting tap conductors. References: Photovoltaic Systems, p. 339-340 NEC Article 230


Tapping Service Conductors

Service conductors may be tapped to make supply side connections, and requires the following: Conductors should be as short as possible with the new PV disconnect

mounted adjacent to the tap point. Conductors should be installed in rigid metal conduit provide the highest

level of fault protection. Service conductors must be sized for at least 125% of the inverter

continuous rated current output. The new service must be properly grounded and bonded.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 339-340 NEC Articles 230 and 240


Load Side Connection

The output of utility-interactive inverters are permitted to be connected on the load side of the service disconnecting means at any distribution equipment on the premises.


To Utility

To Branch Circuits

Service Disconnect


Backfed Circuit Breaker

Presenter

Presentation Notes

Many small residential and commercial PV systems can be interconnected by adding backfed circuit breakers to distribution panels as long as certain conditions are met. References: Photovoltaic Systems, p. 336-339 NEC 690.64, 705.12(D)


Load Side Interconnections

Load side connections for interactive inverters address the following requirements:

Overcurrent protection and disconnects Bus or conductor ratings Ground-fault protection Markings Backfed circuit breakers Fastening Inverter output connection

Presenter

Presentation Notes

Where the distribution equipment is supplied by both the utility and one or more utility-interactive inverters, and where the distribution equipment is capable of supplying multiple branch circuits or feeders, or both, load side connections must comply with seven requirements. References: Photovoltaic Systems, p. 336-339 NEC 690.64, 705.12(D)


Dedicated Overcurrent and Disconnect

Load side connections require each source (inverter) to have a dedicated disconnect and overcurrent protection. Fusible disconnect or circuit breaker; need not be service rated.

PV systems using more than one inverter are considered multiple

sources, and require a dedicated disconnect and overcurrent device for each inverter.

A single disconnecting means can be provided for the combination of multiple parallel inverters connected to subpanels.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 336-339 NEC 690.64, 705.12(D)(1)


Bus or Conductor Rating

Load side connections require that the sum of the ampere ratings of overcurrent devices supplying power to a busbar or conductor does not exceed 120% of busbar or conductor rating.


To Utility

To Branch Circuits

Service Disconnect


Backfed Circuit Breaker

200 A

40 A

Presenter

Presentation Notes

For a typical 200 A residential service with a 200 A panel, up to 40 A of backfed PV breakers would be allowed, allowing a maximum inverter continuous output current rating of 32 A. For interactive PV systems with energy storage intended to supply backup load during grid outages, the bus or conductor loading is evaluated at 125% of the inverter maximum continuous current output rather than the overcurrent device rating. References: Photovoltaic Systems, p. 336-339 NEC 690.64, 705.12(D)(2)


Bus or Conductor Rating: Example

What is the highest rated inverter continuous AC output current

that can be interconnected to a 125 A panel supplied from the grid by a 100 A overcurrent device?

The OCP devices supplying power to the panel (PV and grid) can not exceed 120% of the panel bus rating. The allowable OCP devices is 1.2 x 125 A = 150 A. The allowable PV breaker would then be 150 A – 100 A = 50 A.

Since the PV OCP device needs to be 125% of the inverter

maximum continuous output current ratings, the maximum inverter continuous output current would be 50 A / 1.25 = 40 A.

Presenter

Presentation Notes

This requirement only applies to main breakers and backfed breakers from PV systems that supply power to the busbar. It does not include load circuit breakers. This requirement is intended to prevent potential overload conditions from occurring at the point of connection. References: Photovoltaic Systems, p. 336-339 NEC 690.64, 705.12(D)(2)


Ground-Fault Protection

Interactive inverters must be interconnected on the line side of all

ground-fault protection equipment.

Most ground-fault protection breakers are not listed for backfeeding, and may damage them and prevent proper operation.

Supply side interconnections are usually required for larger facilities incorporating ground-fault protection devices at the service if they are not listed and approved for backfeeding.

Presenter

Presentation Notes

Supply side connections are usually required for larger commercial services having ground-fault protection for the entire service. References: Photovoltaic Systems, p. 336-339 NEC 690.64, 705.12(D)(3)


Marking

Distribution equipment used for interconnecting inverters must

have marking to identify the connection for all sources.

Requires labels for backfed PV breaker and main supply breaker.

Presenter

Presentation Notes



Suitable for Backfeed

Circuit breakers used for inverter connections must be suitable

for backfeeding.

Breakers without “Line” and “Load” side marking have been evaluated in both directions, and considered to be identified as suitable for backfeeding.

Presenter

Presentation Notes



Fastening

Fastening normally required for supply breakers is not required

for breakers supplied by interactive inverters.

Bolt-in connections, or panel covers normally render breakers not readily accessible for removal.

The requirement for listed interactive inverters to de-energize output upon loss of utility voltage also makes these breakers safer for removal and service.

Presenter

Presentation Notes

References: Photovoltaic Systems, p. 336-339 NEC 690.60, 690.64, 705.12(D)(6), 408.36(D)


Inverter Output Connection

If the sum of the overcurrent device ratings supplying a panelboard is greater than 100% of the bus rating:

The inverter output breakers must be installed at the opposite end of the bus from the utility supply breaker, and have a permanent label stating: WARNING: INVERTER OUTPUT CONNECTION – DO NOT RELOCATE THIS

OVERCURRENT DEVICE

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Load Side Connection: Example

Consider a 7 kW PV inverter with 240 V output. Can this inverter

be connected to a 150 A panel supplied by a 150 A main service breaker?

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Reference: Photovoltaic Systems, p. 336-339


Load Side Connection: Example (cont.)

The inverter maximum continuous output current is: 7,000 W / 240 V = 29.2 A

The required overcurrent device rating is:

29.2 A x 125% = 36.5 A rounded up to next standard breaker size, 40 A

The 150 A panelboard permits 120% x 150 A = 180 of supply breakers: 180 A – 150 A main leaves 30 A maximum allowable PV supply breakers.

A 7 kW inverter requires a 40 A breaker and may not be

connected to this panel.

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Load Side Connection: Example (cont.)

To allow the load side connection of a 7 kW inverter for the

previous example, possible solutions include:

Upgrading the panel rating to 200 A with a 200 A main breaker would allow a 40 A backfed breaker from the PV systems. Keeping the main breaker at 150 A would allow even more PV capacity to

be interconnected, and not require a utility service upgrade.

Ultimately, the ratings of distribution equipment and overcurrent protection devices limit the size of load side interconnections.

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Inverter Subpanels

Inverter subpanels are

commonly used for multiple string inverter installations, and can be combined into a single disconnecting means.

Each inverter has a dedicated overcurrent device and panel must be sized for load side interconnection requirements.

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Utility-Scale Interconnections

Large PV systems 500 kW to 1 MW and larger are typically interconnected to the utility grid at distribution voltages.

330-600 Vdc

AC

DC

Distribution Transformer

208 Vac : 480 Vac 480 Vac : 38 kVac

Output Transformer

To Collection System

Inverter PV Array

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Large PV systems are interconnected to primary and secondary distribution systems, and require additional transformers and protective equipment.


Utility Interconnection Agreements

Interactive PV systems require approval from the local electric utility before beginning parallel operations.

Most utilities have standard procedures and agreements for customers to interconnect PV systems, and generally include the following provisions: Use of listed equipment approved for interactive operation Permitting, inspection and approval by the AHJ Size limits and tiers Location of disconnecting means and labeling Insurance and liabilities Metering and billing Testing and monitoring Maintenance Application and processing fees

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Interconnection agreements are a contract between a distributed generation owner (utility customer) and an electric utility, and establish the terms and conditions for the interconnection. Most utilities have simple interconnection agreements for the installation of small PV systems at residential and commercial facilities. Larger commercial installations generally have additional requirements, while solar farms larger than 5 to 10 MW are often owned and operated by utilities themselves. Independently-owned solar generation may be subject to qualifying facility requirements. While the administrative details for interconnection agreements vary between utilities, most have common technical requirements based on national codes and standards. For investor-owned utilities, interconnection rules and policies are often dictated by state public utilities commissions. Although municipal and cooperative utilities may be exempted from state utility commission rules, most follow similar technical guidelines and administrative practices for interconnection as investor-owned utilities. Suggested Exercise: Obtain and review the utility interconnection agreement from your local utility. References: Photovoltaic Systems, p. 342-347 Database of State Incentives for Renewable Energy (DSIRE): www.dsireusa.org


Interconnection Agreements: Code Compliance

Electric utilities require customer-owned PV systems and other

interconnected distributed generation to meet local code requirements.

Listed Interactive Equipment Inverters and motor-generators must be listed and approved for interactive

operations.

Approval PV installations must usually be permitted, inspected and approved by the

Authority Having Jurisdiction (AHJ) prior to beginning interactive operations.

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Utility interconnection agreements include requirements for using listed interactive equipment (inverters), and the installation must be permitted, inspected and approved by the Authority Having Jurisdiction (AHJ). Reference: Photovoltaic Systems, p. 342-347


Interconnection Agreements: Liability Insurance

Electric utilities often require owners of interactive PV systems to

maintain liability insurance to protect the customer and the utility in the event of any accidents, injuries or adverse effects due to the operation of a customer’s PV system. Utilities may also require owners to indemnify the utility for any potential

damages as a result of operation of a PV system.

Customer are also usually required to maintain their equipment in accordance with the interconnection agreement.

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Safety and protections for the public and utility workers will always be a concern for customer-owned distributed generation. Most utilities require the owner to maintain a liability insurance policy to cover any accidents or adverse effects due to the operation of a customer’s PV system. Utilities may also require the PV system owner to indemnify the utility and hold them harmless. Reference: Photovoltaic Systems, p. 342-347


Interconnection Agreements: Testing and Monitoring

Some electric utilities may require special testing or monitoring

for interconnected PV systems, especially for larger installations that may impact grid operations.

Utility testing and monitoring may include: Voltage and frequency output Power quality Anti-islanding protection

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Some utilities may require inspections or testing for PV systems and other distributed generators to ensure they are operating within prescribed voltage and frequency limits, especially for installations larger than 100 kW. For rotating generators, utilities usually require the use of protective relaying equipment to isolate the equipment from the grid if either operate outside allowable limits. All interactive PV inverters have integral anti-islanding protection that disconnects their output to the grid if the inverter output or grid are not operating within the prescribed limits. Reference: Photovoltaic Systems, p. 342-347


Interconnection Agreements: Disconnecting Means

For code compliance, interactive PV systems must already have

a disconnect means to isolate the inverter output from the utility grid.

Utilities may also require that PV system disconnects are: External to a building Lockable by utility personnel Provide a visible-break isolation from the grid

In some cases, small residential PV systems may not be required to have a utility-accessible disconnect.

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Utilities may require disconnects for PV systems that are external to a building, lockable by utility personnel, and provide a visible-break isolation from the grid. In accordance with NEC Article 690, interactive inverters already must have a manual means of isolation from the grid, and must automatically disconnect if grid voltage is lost. All inverters listed to UL1741 employ anti-islanding provisions to disconnect from the grid automatically. If the PV system disconnect is not co-located with the utility service disconnect, a directory and map of the facility must be provided indicating the location of the PV disconnect. This disconnect means can usually be located to meet utility requirements. Generally, additional utility disconnects are not required for small residential PV systems, but are usually required for commercial installations 10 to 100 kW and larger. Utility disconnects are intended for safety, but in some cases may be used for administrative purposes by locking out a distributed generator that does not comply with the terms and conditions of their interconnection agreement. References: Photovoltaic Systems, p. 342-347 NEC 690, 705


Interconnection Agreements: Metering and Billing

Different configurations and types of revenue metering may be

used to record energy flows for facilities with PV systems, based on the type of billing arrangements. Demand metering Time-of-use metering PV output metering Net purchase and sale metering (dual metering) Net metering

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Different arrangements and types of metering may be used to record energy flows for facilities with PV systems, depending on the size and type of system, interconnection policies, and the intended revenue structure. Reference: Photovoltaic Systems, p. 340-342


Electronic Metering

Electronic utility meters can measure and record many parameters in separate registers, including:

Energy delivered to a facility Energy received from a facility Peak power demand Time-of-use consumption Reactive power and energy Power factor

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Electronic metering is becoming more prevalent and allows utilities to monitor and record a number of parameters in addition to the energy delivered. Electronic watt-hour meters use current transformers (CTs) and voltage transformers (VTs) to measure current and voltage, and contain small microprocessors to collect and record data. Many electronic meters can also be used for automated meter reading (AMR) applications, allowing the meter data to be read remotely by RF signals, telephone modems, network or power line carrier signals. Reference: Photovoltaic Systems, p. 340-342


Revenue Metering

Revenue metering is installed at

the point of service entrance for utility billing purposes, and records the energy (kWh) delivered to a facility.

Revenue metering establishes the transition between the utility and customer-owned equipment.

Electric Utility

Customer Loads

kWh Meter spins in one direction, customer pays retail rate for energy

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Revenue metering measures and records the energy delivered to a customer’s facility for billing purposes at the point of service entrance. The customer is billed at the retail rate per kWh for energy consumed. Utilities often have different rate tiers for different levels of energy consumption, and for residential or commercial customers. For example, to promote energy conservation, a lower rate might apply to residential monthly energy consumption up to 1000 kWh, and a higher rate for usage over 1000 kWh. Reference: Photovoltaic Systems, p. 340-342


Demand Metering

Demand metering is often used

for larger commercial and industrial facilities, and records the peak power (kW) delivered over any 15-minute interval during a month.

Electric Utility

Customer Loads

kWh + kW Customer pays for energy and peak power demand

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Demand metering is installed on most larger commercial and industrial facilities, and customers are billed monthly for the peak power (kW) demand in addition to energy consumption (kWh). Different tiers and higher rates usually apply to customers having greater peak loads. The peak power consumption over a defined interval, usually 15 minutes, sets the peak demand charges for the month. Large industrial facilities with low power factor may also be metered and billed for reactive power and energy, using VAR meters. Reference: Photovoltaic Systems, p. 340-342


Time-of-Use Metering

Time-of-use metering uses

electronic meters to record energy flows based on the time of day it is consumed.

Electric Utility

Customer Loads

kWh vs. Time Customer pays different rates for energy based on time

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Time-of-use metering uses electronic meters to record energy use in separate registers for different times of the day, corresponding to on-peak and off-peak times for the utility. The customer is billed at lower rates for energy used during off-peak times than for on-peak times. Time-of-use metering is generally optional, but may be increasingly required as a form of demand metering. This type of metering encourages a customer to curtail energy use during peak times, or to shift the use of major loads to off-peak times. Consequently, time-of-use rates also encourage the adoption of energy management and distributed energy storage systems. Reference: Photovoltaic Systems, p. 340-342


PV Output Metering

The energy production for PV

systems is often metered independently for feed-in tariffs or renewable energy credits. For feed-in tariff programs, the PV

output and metering are connected on the utility side of the revenue meter.

Electric Utility

Customer Loads

Load kWh This meter records

energy to facility

PV kWh PV System

This meter records energy from PV system

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PV output metering uses a dedicated meter to record the energy production from PV systems independently. For feed-in tariff programs that pay the customer separately for PV generation, the PV output and metering are connected to the utility side of normal utility revenue metering. Since the customer is paid directly for the PV generation, the energy is not supplied to the load side of the normal utility revenue meter. PV output metering is also required to document production for renewable energy credits. Reference: Photovoltaic Systems, p. 340-342


Sub Metering

Bimodal and hybrid PV systems with multiple AC input and output circuits may use sub metering to measure energy delivered to loads or produced by other power sources.

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Dual Metering

Dual metering (net purchase and sale metering) uses two unidirectional meters (or single electronic meter) to record energy flow to and from the utility and facility with PV generation.

One meter register records electricity drawn from the grid; user pays retail

rate. The other meter register records electricity fed back onto the grid; user is

credited wholesale rate.

To Utility

Facility with PV Generation kWh + kWh - Electric Utility

To Facility

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Dual metering (net purchase and sale metering) uses two unidirectional meters (or an electronic meter) to record energy flow to and from a facility. One meter registers electricity drawn from the grid and the customer pays retail rate for this energy. The other meter records energy fed back into the grid for which the customer is credited the wholesale rate (avoided cost). Two electromechanical meters can be wired in series, and use detents to prevent them from recording when the power is flowing in the opposite direction. More commonly today, a single electronic meter that measures positive and negative energy flows is used. There is usually a significant difference in the retail rate and the avoided cost. A typical retail rate might be 12¢/kWh, while the avoided cost may be 4¢/kWh. Consequently, dual metering is less favorable for renewable generators when production exceeds the facility loads. If all PV energy is consumed on site and none is sent back into the grid, dual metering has the same result on utility billing as net metering. For example, assume a customer has a PV system that produces 30 kWh/day, of which 10 kWh is consumed on site and 20 kWh is sent back to the grid. Under a dual metering arrangement, 10 kWh will offset the full retail energy costs, while the 20 kWh send back to the grid will only be credited at a lower wholesale rate, regardless if that energy is later used at the facility or not. Reference: Photovoltaic Systems, p. 340-342


Net Metering

Net metering allows the utility customer to receive full retail

credit for at least a portion of the excess energy produced from a PV systems and sent back to the utility grid.

Utility meter spins in both directions, effectively banking excess production

on the grid for future credit.

A single, bi-directional meter records net energy

Facility with PV Generation kWh net Electric Utility

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Net metering allows a certain amount of excess energy generated from PV systems or other distributed generators to be sent onto the grid, for which the customer receives full retail credit. This credit can be later used to offset facility loads. Most utilities allow monthly carryover energy credits, and the customer may or may not be compensated for excess generation over time. This affects the value of larger PV systems that consistently produce more energy than the facility loads require. Some utilities may pay the customer wholesale rate or even full retail rate for excess generation, depending on the local interconnection policies. For example, assume a customer has a PV system that produces 30 kWh/day, of which 10 kWh is consumed on site and 20 kWh is sent back to the grid. Under a net metering arrangement, the 20 kWh sent back to the grid is credited at retail price, up to certain limits. Net metering s arrangement is more advantageous to the customer than a dual meter net purchase and sale arrangement. Reference: Photovoltaic Systems, p. 340-342


State policy

Voluntary utility program(s) only

www.dsireusa.org / November 2010

* State policy applies to certain utility types only (e.g., investor-owned utilities)

WA: 100

OR: 25/2,000*

CA: 1,000*

MT: 50*

NV: 1,000*

UT: 25/2,000*

AZ: no limit*

ND: 100*

NM: 80,000*

WY: 25*

HI: 100 KIUC: 50

CO: no limit co-ops & munis: 10/25

OK: 100*

MN: 40

LA: 25/300

AR: 25/300

MI: 150* WI: 20*

MO: 100

IA: 500*

IN: 10* IL: 40*

FL: 2,000*

KY: 30*

OH: no limit*

GA: 10/100

WV: 25/50/500/2,000

NC: 1,000*

VT: 20/250/2,200

VA: 20/500*

NH: 100 MA: 60/1,000/2,000* RI: 1,650/2,250/3,500*

CT: 2,000* NY: 10/25/500/2,000* PA: 50/3,000/5,000* NJ: no limit*

DE: 25/500/2,000*

MD: 2,000

DC: 1,000

Note: Numbers indicate individual system capacity limit in kW. Some limits vary by customer type, technology and/or application. Other limits might also apply. This map generally does not address statutory changes until administrative rules have been adopted to implement such changes.

NE: 25

KS: 25/200*

ME: 660 co-ops & munis: 100

PR: 25/1,000

AK: 25*

43 states + DC & PR have adopted a net

metering policy

DC

Net Metering Rules

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Net metering in an incentive for renewable power generation, and does not apply to systems larger than permitted under local interconnection and net metering rules. Nearly every state has net metering rules applying to PV systems and other types of renewable generation. Different size limits and tiers apply for different utilities and states, ranging from 10 kW residential to over 2 MW. Reference: www.dsireusa.org


Summary

The technical and safety requirements for the interconnection of

PV systems to the utility grid are governed by national codes and standards.

Small PV systems can usually be connected on the load side of the service disconnect means, while larger systems are usually interconnected on the supply side.

Policies and interconnection agreements are specific to states

and utilities.

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Questions and Discussion

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Utility Interconnection - Energy Consultants Group · 2018. 3. 1. · IEEE 1547 Standard for...

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