Net Metering and Utility Interconnection

Presented by:

Bill BrooksBrooks Engineering

Technical Interconnection Issues: Codes and Standards

Who Has a stake in the PV Industry?

Million Solar Roofs Partnerships Electric utility companies Electric customers wanting to install

a PV system PV component manufacturers PV equipment and system dealers Local jurisdictions enforcing building

codes

Why Do We Need PV Codes and Standards?

To facilitate the broad acceptance of the technology among local jurisdictions and interconnecting utilities.

To maintain minimum requirements for PV products and their installation.

To standardize and reduce the cost of testing and certification.

Who sets codes and standards?

National Fire Protection Association (NFPA)• National Electrical Code (NEC)

- Electrical Power System Installation--developed in conjunction with electrical trade and industry experts.

Underwriters Laboratory (UL)• Standards for Electrical Equipment Safety--developed in

conjunction with manufacturers. Institute of Electrical and Electronic Engineers

(IEEE)• Standards for electrical and electronic equipment--

developed in conjunction with applicable industry experts.

International (IEC, CENELEC, etc…)

What are the applicable codes and standards for PV systems?

NEC Article 690 - Solar Photovoltaic Systems - Building codes - UBC, SBC, BOCA, local codes

UL Standard 1703, Flat-plate Photovoltaic Modules and Panels

IEEE 929-2000, Recommended Practice for Utility Interface of Photovoltaic (PV) Systems (approved in January 2000)

UL Standard 1741, Standard for Static Inverters and Charge Controllers for Use in Photovoltaic Power Systems (published in May 1999)

What are the common interests of Utilities and PV manufacturers?

Provides predictable requirements for design and installation.• Utility protection departments need to reduce

costs.• Inverter manufacturers need to standardize their

designs to keep costs lower. Over 3000 utilities with a similar number of

interconnection requirements.• Consensus IEEE standard makes it unnecessary

for utilities to utilize an independent standard.• Inverter manufacturers can build one design that

is widely applicable.

Utility Interconnection Issues

Personnel safety Equipment protection Service reliability Power quality

Utility Interconnection Requirements

IEEE standard 929 UL standard 1741 Utility practice and requirements Public utility commission statutes

UL 1741 Standard for Static Inverters and Charge Controllers for Use in Photovoltaic Power Systems

First released in May of 1999

Has been revised to match IEEE 929-2000

Compliance with revised document required on November 7, 2000)

New title reads “Standard for inverters, converters, and controllers for use in Independent Power Systems.”(Nov 8)

Underwriters Laboratories Inc.®

Subjects 1741 333 Pfingsten RoadNorthbrook, IL 60062March 3, 1999

TO: Industry Advisory Group of Underwriters Laboratories Inc. for Power Conditioning Units for Use in Residential Photovoltaic Power Systems,Electrical Council of Underwriters Laboratories Inc.,Subscribers to UL's Listing Services for Photovoltaic Charge Controllers (QIBP),Subscribers to UL's Listing Services for Photovoltaic Power Systems Accessories (QIIO),Subscribers to UL's Listing Services for Power Conditioning Units for Use in Residential Photovoltaic Power Systems (QIKH), andSubscribers to UL's Listing Services for AC Modules (QHYZ)

SUBJECT: Request for Comments on the Proposed First Edition of the Standard for StaticInverters and Charge Controllers, UL 1741; PROPOSED EFFECTIVE DATE

Attached as Appendix A for your review and comment are proposed requirements for UL 1741.Questions regarding interpretation of requirements should be directed to the responsible UL Staff.Please see Appendix B of this bulletin regarding designated responsibility for the subject productcategories.

Please note that proposed requirements are of a tentative and early nature and are for reviewand comment only. Current requirements are to be used to judge a product until theserequirements are published in final form.PROPOSED EFFECTIVE DATE

The proposed requirements will necessitate a review and possible retest of currently Listedproducts. Therefore, UL proposes that the new requirements become effective 18 months afterpublication. This is intended to provide manufacturers with sufficient time to submit modifiedproducts for investigation and to implement the necessary changes in production. Please notethat this also includes the time that will be needed by UL to conduct a review of the modifiedproduct.

RATIONALE

The first edition of the Standard for Static Inverters and Charge Controllers for Use inPhotovoltaic Power Systems, UL 1741, was proposed in the subject bulletin dated August 1,1997. The proposed Standard has been significantly revised since then. The revisions are aresult of the comments UL received from industry members regarding the proposed draft. Inaddition, the revisions were made to align the proposed Standard with the Ninth Draft ofRecommended Practice for Utility Interface of Photovoltaic (PV) Systems, P929, and other ULStandards. This bulletin proposes the revised first edition of the Standard for Static Inverters andCharge Controllers for Use in Photovoltaic Power Systems, UL 1741.

UL®

What is UL 1741 and how does it relate to IEEE 929?

First official version published in May of 1999. “Final” version released November of 2000.

1741 incorporates the testing required by IEEE 929 (frequency and voltage limits, power quality, non-islanding inverter testing)

1741 testing includes design (type) testing and production testing. Line-tie inverters should have the words

“Utility-Interactive” printed directly on the listing label—this makes identification of the listing much more straightforward (several inverter manufacturers currently using this designation).

How Does a Utility, or a PV-System Purchaser, Know If An Inverter Meets The Requirements of IEEE 929?

If it meets the testing requirements of test standard UL 1741

and has the words “Utility-Interactive” printed directly on the listing label

Terms and Conditions for Interconnection

May involve the following:• Metering options• Size restrictions on metering options• Carryover credit on monthly billings• Net Meter or differing buy and sell rates• Outdoor disconnect requirements• Insurance requirements• Interconnection costs

Net Metered Systems in California(Similar to some other states)

Requires a contract with the serving utility company.

Inverter must be acceptable to utility for interconnection.

Utility also may have a list of acceptable manual disconnects to choose from.

Starting January 1, 1999, systems are to be billed on annual basis.

Starting January 1, 2001, systems may elect time-of-use net metering (up to 30% increased financial benefit)

P929Recommended Practice forUtility Interface ofPhotovoltaic (PV) Systems

Prepared by the Utility Working Group ofStandards Coordinating Committee 21, on Photovoltaics

Copyright © 1998 by the Institute of Electrical and Electronic Engineers, Inc.345 East 47th StreetNew York, NY 10017, USAAll Rights Reserved

This is an IEEE Standards Project, subject to change. Permission is hereby granted forIEEE Standards committee participants to reproduce this document for purposes ofIEEE standardization activities, including balloting and coordination. If this documentis to be submitted to ISO or IEC, notification shall be given to the IEEE CopyrightsAdministrator. Permission is also granted for member bodies and technical committeesof ISO and IEC to reproduce this document for purposes of developing a nationalposition. Other entities seeking permission to reproduce portions of this document forthese or other uses must contact the IEEE Standards Department for the appropriatelicense. Use of information contained in the unapproved draft is at your own risk.

IEEE Standards DepartmentCopyrights and Permissions445 Hoes Lane, P.O. Box 1331Piscataway, NJ 08855-1331, USA

IEEE 929-2000

Passed by IEEE Standards Board in January, 2000.

Represents an excellent primer on PV inverter interconnection issues.

The Need for PV Interconnection Standards

Many utilities were using “Rotating Machinery” requirements for PV systems

Many of the Interconnection Requirements were established in early “PURPA” days• too many requirements

• telemetery and “Utility Grade” type relays

• special (and costly) engineering were needed for each specific utility requirements

Purpose of IEEE 929

“This recommended practice contains guidance regarding equipment and functions necessary to ensure compatible operation of photovoltaic systems which are connected in parallel with the electric utility. This includes factors relating to personnel safety, equipment protection, power quality and utility system operation.”

• Power Quality

• Safety and Protection

IEEE 929 Working Group Consisted of Utilities and Industry

John Stevens, ChairSandia National Labs

D. Lane GarrettSouthern Co. Services

Miles Russell, Secr.Ascension Technology

Mike BehnkeTrace Technology

Steve Hester,

UPVGJohn MoriartyRaytheon

Bill BrooksN. Carolina Sol. Center

John Hoffner, Planergy(ex Austin Electric)

Chet NapikoskiArizona Public Service

John BzuraNew England Electric

Barry HornbergerPECO Energy

Jean PosbicSolarex

Steve Chalmers (Ret.)Salt River Project

Bob JonesRochester G&E

Jodi SmytheUnderwriters Labs

Joe ChauFlorida Power & Light

Greg KernAscension Technology

Chase SunPacific Gas and Electric

Doug Dawson (Ret.)Southern Cal Edison

Leslie LibbyAustin Electric

Rick WestUPG

Dick DeBlasioChair – IEEE SCC 21

Don LowebergIPP

Chuck WhitakerEndecon

Tom DuffyCentral Hudson G&E

Tron MelzlOmnion

Robert WillsAdvanced Energy Sys.

Chris FreitasTrace Engineering

Tim ZgonenaUnderwriters Labs

What Does IEEE 929Really Impact?

PV Array

InverterM

UtilitySystem

IEEE 929 Outline

Introduction 1. Overview (scope & purpose) 2. References 3. Definitions (inverter, islanding, PCC,

quality factor, etc…) 4. Power quality 5. Safety and protection functions Annexes

Power Quality

Power quality problems in general are rising because of proliferation of non-linear loads on utility systems -- all customers suffer

PV should not add to that problem

Power Quality

• Power Quality• 1. Service Voltage• 2. Voltage Flicker• 3. Frequency• 4. Waveform Distortion

• IEEE 519

• 5. Power Factor

Safety and Protection Functions

1. Response to Abnormal Utility Conditionsa. Voltage Disturbancesb. Frequency Disturbances c. Islanding Protectiond. Reconnect After a Utility Disturbance

2. Direct Current Isolation 3. Grounding 4. Manual Disconnect

Response to Abnormal Utility Conditions

Voltage (at PCC) Maximum Trip Time* V< 60 (V<50%) 6 cycles 60V<106 (50%V<88%) 120 cycles

106V132 (88%V110%) Normal Operation 132<V<165 (110%<V<137%) 120 cycles

165V (137%V) 2 cycles

Frequency (at PCC) Maximum Trip Time* <59.3 Hz 6 cycles

59.3 - 60.5 Hz (normal) -- >60.5 Hz 6 cycles

*”Trip time” refers to the time between the abnormal condition being applied and the inverter ceasing to energize the utility line. The inverter will actually remain connected to the utility to allow sensing of utility electrical conditions for use by the “reconnect” feature.

Terminology

Power Conditioning Unit or Inverter• Line-Commutated Inverters• Self-Commutated Inverters• Inverter Shut Down• The PV Inverter as a UPS• Power Factor• Controls Integrated into the Inverter

Islanding

The PV Inverter as a UPS

Some inverters are designed to provide uninterruptible power to critical loads

The power to critical loads is maintained when the connection to the utility is severed

When the inverter ceases to energize the utility line (due to abnormal conditions, the inverter will continue to maintain the loads connected to a special distribution panel isolated from the utility, also no power flows to the utility

IEEE 929- Annexes

• Annex A (Normative) – Minimum Test Procedure for a Non-Islanding PV Inverter

• Annex B (Informative) - Bibliography

• Annex C - PV Inverters and the Utility Interface (Terminology)

• Annex D - Disconnect Switches & Utility Procedures

• Annex E - Islanding as it Applies to PV Systems

• Annex F - The PV Inverter Under Utility Fault Conditions

• Annex G - Dedicated Distribution Transformer

ManualDisconnect Switch

PV Array

InverterM

LocalLoads

UtilitySystem

Islanding Testing

Why do we need testing?

Utility engineers are required to do testing of system protection equipment

Testing has a profound impact on an engineer’s understanding of how things work.• Example: New York utilities require special tests.

º Tests designed to pit PV inverters against notorious NY waveforms

º Three utility engineers from NY visited Sandia to witness tests

º After first day into three-day test procedure, they said, “Let’s do something more interesting.”

Anti-Islanding Requirements

“Typical” island (no balance between load and island)• Trip time - 10 cycles (to avoid interference with reclosing)

“Balanced” island (real power load between 50% and 150% of PV output, Q 2.5)• Trip time - 2 seconds

“non-islanding” test procedure:

The load should have a real power match as close as reasonable (at least within 20%) to the PV system output

and a Q (quality factor) 2.5, where Q=R(C/L)½

the selected Q 2.5 equates to an uncorrected power factor of 0.37. As power factor increases, Q decreases. Thus, the test requirement that Q 2.5 equates to lines with uncorrected power factors from 0.37 to unity

RLC load that has been tuned to 60Hz

Sandia Anti-Islanding Method Basic Concepts

Frequency and voltage trip points are used Error signal from frequency and voltage is

calculated each ½ cycle Frequency and voltage are then “tweaked” in the

same direction as error signal If tweaking results in change, then accelerated

tweaking results to push frequency or voltage to trip points

Test Circuit Used at Sandia

Inv#1

Inv#2

secondarydisconnect

primarydisconnect

distributiontransformer

R C L Inv#3

LMutility

“Less Than Sandia” SchemeBalanced load and generation (25% of Capacity)

25% Load 25% Gen Q=2.5

57

58

59

60

61

62

63

0 1 10 100 1000

Trip Time (cycles)

Fre

qu

ency

(H

z)

94

99

104

109

114

119

124

Vo

ltage (V

)

Voltage

Frequency

“Less Than Sandia” Scheme(125% of Inverter Capacity)

125% Load 100% Gen, Q=2.5

57

58

59

60

61

62

63

0 1 10 100 1000

Trip Time (cycles)

Fre

qu

en

cy (

Hz)

80

85

90

95

100

105

110

115

120

Vo

ltag

e (

V)

Voltage

Frequency

“Less Than Sandia” Scheme Balanced load and generation (100% Capacity)

100% Load 100% Gen, Q=2.5

57

58

59

60

61

62

63

0 1 10 100 1000

Trip Time (cycles)

Fre

qu

en

cy

(H

z)

94

99

104

109

114

119

124

Vo

lta

ge (

V)

Voltage

Frequency

Sample Test-Using Sandia Anti-Islanding Method

Note that trip time meets “typical” criteria even though test is with “balanced” conditions

SFS + SVSLoad: L+C, Qres = 3.7

108

112

116

120

124

128

132

0 1 10 100

Trip Time (cycles)

Vo

lta

ge

(V

)

Sample Motor Load Tests—Using Sandia Anti-Islanding MethodRequired trip time - 2 seconds

SFS + SVSLoad: Motor + C

565758596061626364

0 1 10 100

Trip Time (cycles)

Fre

que

ncy (

Hz)

Motor Load TestsGeneration to load ratio impacts

SFS + SVSLoad: Motor + C

0

10

20

30

40

50

60

70

80

0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20

Generation / Load Ratio

Tri

p T

ime

(cy

cles

)

IEEE 1547

Standard for Interconnecting Distributed Resources with

Electric Power Systems

Approved at June 2003 IEEE Standards Board Meeting

1. Standards: documents with mandatory requirements (shall)

2. Recommended Practices: documents in which procedures and positions preferred by the IEEE are presented (should)

3. Guides: documents in which alternative approaches

to good practice are suggested but no clear-cut recommendations are made (may)

IEEE Standards are Voluntary.

IEEE Standards Classification

1547 Standard for Interconnecting Distributed Resources with Electric Power Systems

1547.1 Draft Standard for Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems

P1547.2Draft Application Guide for IEEE P1547 Draft Standard for Interconnecting Distributed Resources with Electric Power Systems

Guide for NetworksGuide for Impacts

Guide for Islanding & Anti-Islanding

DP Specifications and Performance

Guide For

Interconnection System

Certification

P1547.3Draft Guide for Monitoring, Information Exchange and Control of DR Interconnected with EPS

The above schematic identifies existing standards development projects and potential future activities under discussion by P1547 Work Group members.

1547 Body of Standards

1547: Interconnection Is The Focus

Distributed Resource

(DR) unit

Area Electric Power

System (EPS)

Interconnection

System

Local EPS 1

Area Electric Power System (EPS)

Local EPS 3

PCC

Point of DR Connection

DR unit

Local EPS 2

Point of DR Connection

Point of Common Coupling (PCC)

Note: There can be any number of Local EPSs.

PCC

DR unit Load Load

1547 Interconnection Terms

INTRODUCTION

1.0 OVERVIEW 1.1 Scope 1.2 Purpose 1.3

Limitations

2.0 REFERENCES

3.0 DEFINITIONS

IEEE 1547 Contents

IEEE 1547 Contents

1.1 ScopeThis standard establishes criteria and requirements for interconnection of distributed resources (DR) with electric power systems (EPS).

1.2 PurposeThis document provides a uniform standard for interconnection of distributed resources with electric power systems. It provides requirements relevant to the performance, operation, testing, safety considerations, and maintenance of the interconnection.The requirements shall be met at the point of common coupling (PCC), although the devices used to meet these requirements can be located elsewhere. This standard applies to interconnection based on the aggregate rating of all the DR units that are within the Local EPS. The functions of the interconnection system hardware and software that affect the Area EPS are required to meet this standard regardless of their location on the EPS.The stated specifications and requirements, both technical and testing, are universally needed for interconnection of DR, including synchronous machines, induction machines, or power inverters/converters, and will be sufficient for most installations.1

1 Additional technical requirements and/or tests may be necessary for some limited situations.

4.0 INTERCONNECTION TECHNICAL SPECIFICATIONS AND REQUIREMENTS

4.1 General Requirements 4.2 Response to Area EPS Abnormal Conditions4.3 Power Quality 4.4 Islanding

5.0 INTERCONNECTION TEST SPECIFICATIONS AND REQUIREMENTS

5.1 Design Test 5.2 Production Tests 5.3 Interconnection Installation Evaluation 5.4 Commissioning Tests

5.5 Periodic Interconnection Tests ANNEX A (INFORMATIVE) BIBLIOGRAPHY

IEEE 1547 Contents

IEEE 1547 Contents

4.1 General Requirements4.1.1 Voltage Regulation (Don’t!)4.1.2 Integration with Area EPS Grounding (Coordinate)4.1.3 Synchronization (<5% voltage fluctuation, no flicker)4.1.4 Distributed Resources on Distribution Secondary Grid and

Spot Networks4.1.4.1 Distribution Secondary Grid Networks4.1.4.2 Distribution Secondary Spot Networks

4.1.5 Inadvertent Energization of the Area EPS (Don’t!)4.1.6 Monitoring Provisions4.1.7 Isolation Device (Disconnect Switch)4.1.8 Interconnect Integrity

4.1.8.1 Protection from Electromagnetic Interference (C37.90.2)4.1.8.2 Surge Withstand Performance (C62.41 or C36.90.1)4.1.8.3 Paralleling Device (withstand 220% of rated voltage)

IEEE 1547 Contents

4.2 Response to Area EPS Abnormal Conditions4.2.1 Area EPS Faults (detect faults, cease to energize)4.2.2 Area EPS Reclosing Coordination (coordinate)4.2.3 Voltage (<60V,106V – 132V, >144V)4.2.4 Frequency (59.3 – 60.5 Hz)4.2.5 Loss of Synchronism (not required unless there is flicker)4.2.6 Reconnection To Area EPS (up to 5 min, C84.1 Range B)

4.3 Power Quality4.3.1 Limitation of DC Injection (>0.5% of rated output current)4.3.2 Limitation of Flicker Induced by the DR (Don’t)4.3.3 Harmonics (~IEEE 519)

4.4 Islanding4.4.1 Unintentional Islanding (Don’t)4.4.2 Intentional Islanding (Don’t know)

Acrobat Document

IEEE 1547 Contents

5.0 INTERCONNECTION TEST SPECIFICATIONS AND REQUIREMENTS

5.1 Design Test5.1.1 Response to Abnormal Voltage and Frequency5.1.2 Synchronization5.1.3 Interconnect Integrity Test5.1.3.1 Protection From Electromagnetic Interference

(EMI)5.1.3.2 Surge Withstand Performance5.1.3.3 Paralleling Device

5.1.4 Unintentional Islanding 5.1.5 Limitation of DC Injection5.1.6 Harmonics

5.2 Production Tests

IEEE 1547 Contents

5.3 Interconnection Installation Evaluation5.3.1 Grounding Integration with Area Electric Power System5.3.2 Isolation Device5.3.3 Monitoring Provisions5.3.4 Area EPS Faults5.3.5 Area EPS Reclosing Coordination.

5.4 Commissioning Tests5.4.1 Unintentional Islanding Functionality Test

5.4.1.1 Reverse-Power or Minimum Power Test5.4.1.2 Non-Islanding Functionality Test75.4.1.3 Other Unintentional Islanding Functionality Tests

5.4.2 Cease to Energize Functionality Test

5.5 Periodic Interconnection Tests

Title Scope & Purpose P1547 Draft Standard for Interconnecting Distributed Resources with Electric Power Systems.

• This Standard establishes criteria and requirements for interconnection of distributed resources (DR) with electric power systems (EPS). • This document provides a uniform standard for interconnection of distributed resources with electric power systems. It provides requirements relevant to the performance, operation, testing, safety considerations, and maintenance of the interconnection.

P1547.1 Draft Standard for Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems.

• This Standard specifies the type, production, and commissioning tests that shall be performed to demonstrate that interconnection functions and equipment of a distributed resource (DR) conform to IEEE Std 1547. • Interconnection equipment that connects distributed resources (DR) to an electric power system (EPS) must meet the requirements specified in IEEE Standard P1547. Standardized test procedures are necessary to establish and verify compliance with those requirements. These test procedures must provide both repeatable results, independent of test location, and flexibility to accommodate a variety of DR technologies.

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SCC21 Interconnection Projects

Title Scope and Purpose P1547.2 Draft Application Guide for IEEE Standard 1547 for Interconnecting Distributed Resources with Electric Power Systems

• This Guide provides technical background and application details to support the understanding of IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems. • This document facilitates the use of IEEE 1547 by characterizing the various forms of distributed resource technologies and the associated interconnection issues. Additionally, the background and rationale of the technical requirements are discussed in terms of the operation of the distributed resource interconnection with the electric power system. Presented in the document are technical descriptions and schematics, applications guidance and interconnection examples to enhance the use of IEEE 1547.

P1547.3: Draft Guide for Monitoring, Information Exchange and Control of Distributed Resources Interconnected with Electric Power Systems

• This document provides guidelines for monitoring, information exchange, and control for distributed resources (DR) interconnected with electric power systems (EPS). • This document facilitates the interoperability of one or more distributed resources interconnected with electric power systems. It describes functionality, parameters and methodologies for monitoring, information exchange and control for the interconnected distributed resources with, or associated with, electric power systems. Distributed resources include systems in the areas of fuel cells, photovoltaics, wind turbines, microturbines, other distributed generators, and, distributed energy storage systems.

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SCC21 Interconnection Projects

• Dr. Richard DeBlasio email: ddeblasi@nrel.gov voice: (303) 275 - 4333• Mr. Tom S. Basso email: thomas_basso@nrel.gov voice: (303) 275 - 3753 • IEEE SCC21 -- IEEE Standards Coordinating Committee 21 on Fuel Cells, Photovoltaics, Dispersed Generation, & Energy Storage http://grouper.ieee.org/groups/scc21/• P1547 Draft Standard for Interconnecting Distributed Resources

with Electric Power Systems -- web site and archives http://grouper.ieee.org/groups/scc21/1547 http://grouper.ieee.org/groups/scc21/1547/archives/

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NREL1617 Cole Blvd. MS-1614Golden, CO 80401-3393http://www.nrel.gov

SCC 21 Contact Information