Net%20Metering%20and%20Utility%20Interconnection

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Net Metering and Utility Interconnection
Presented by Bill Brooks Brooks Engineering
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Technical Interconnection Issues Codes and
Standards
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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

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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.

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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)

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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)

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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.

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Utility Interconnection Issues

• Personnel safety
• Equipment protection
• Service reliability
• Power quality

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Utility Interconnection Requirements

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

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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)

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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
  wordsUtility-Interactive printed directly on
  the listing labelthis makes identification of
  the listing much more straightforward (several
  inverter manufacturers currently using this
  designation).

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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
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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

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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)

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IEEE 929-2000

• Passed by IEEE Standards Board in January, 2000.
• Represents an excellent primer on PV inverter
  interconnection issues.

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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

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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

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IEEE 929 Working Group Consisted of Utilities
and Industry
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What Does IEEE 929Really Impact?
PV Array
Utility System
M
Inverter
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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

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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

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Power Quality

• Power Quality
• 1. Service Voltage
• 2. Voltage Flicker
• 3. Frequency
• 4. Waveform Distortion
• IEEE 519
• 5. Power Factor

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Safety and Protection Functions

• 1. Response to Abnormal Utility Conditions
• a. Voltage Disturbances
• b. Frequency Disturbances
• c. Islanding Protection
• d. Reconnect After a Utility Disturbance
• 2. Direct Current Isolation
• 3. Grounding
• 4. Manual Disconnect

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Response to Abnormal Utility Conditions
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.
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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

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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

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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

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ManualDisconnect Switch
PV Array
Local Loads
Utility System
M
Inverter
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Islanding Testing
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Why do we need testing?

• Utility engineers are required to do testing of
  system protection equipment
• Testing has a profound impact on an engineers
  understanding of how things work.
• Example New York utilities require special
  tests.
• Tests designed to pit PV inverters against
  notorious NY waveforms
• Three utility engineers from NY visited Sandia to
  witness tests
• After first day into three-day test procedure,
  they said, Lets do something more interesting.

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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

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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 QR(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

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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

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Test Circuit Used at Sandia
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Less Than Sandia SchemeBalanced load and
generation (25 of Capacity)
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Less Than Sandia Scheme(125 of Inverter
Capacity)
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Less Than Sandia Scheme Balanced load and
generation (100 Capacity)
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Sample Test-Using Sandia Anti-Islanding
MethodNote that trip time meets typical
criteria even though test is with balanced
conditions
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Sample Motor Load TestsUsing Sandia
Anti-Islanding MethodRequired trip time - 2
seconds
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Motor Load TestsGeneration to load ratio impacts
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IEEE 1547

• Standard for Interconnecting Distributed
  Resources with Electric Power Systems
• Approved at June 2003 IEEE Standards Board
  Meeting

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IEEE Standards Classification

• Standards documents with
• mandatory requirements (shall)
• Recommended Practices documents in which
• procedures and positions preferred
• by the IEEE are presented (should)
• Guides documents in which alternative approaches
• to good practice are suggested but
• no clear-cut recommendations are made (may)
• IEEE Standards are Voluntary.

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1547 Body of Standards
1547 Standard for Interconnecting Distributed
Resources with Electric Power Systems
Guide for Networks
Guide for Impacts
P1547.3 Draft Guide for Monitoring, Information
Exchange and Control of DR Interconnected with
EPS
Guide for Islanding Anti-Islanding
Guide For Interconnection System Certification
1547.1 Draft Standard for Conformance Test
Procedures for Equipment Interconnecting
Distributed Resources with Electric Power Systems

P1547.2 Draft Application Guide for IEEE P1547
Draft Standard for Interconnecting Distributed
Resources with Electric Power Systems
DP Specifications and Performance
The above schematic identifies existing
standards development projects and potential
future activities under discussion by P1547 Work
Group members.
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1547 Interconnection Is The Focus
Area Electric Power System (EPS)
Interconnection System
Distributed Resource (DR) unit
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1547 Interconnection Terms
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IEEE 1547 Contents

• INTRODUCTION
• 1.0 OVERVIEW
• 1.1 Scope
• 1.2 Purpose
• 1.3 Limitations
• 2.0 REFERENCES
• 3.0 DEFINITIONS

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IEEE 1547 Contents

• 1.1 Scope
• This standard establishes criteria and
  requirements for interconnection of distributed
  resources (DR) with electric power systems (EPS).
• 1.2 Purpose
• 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.
• 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.

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IEEE 1547 Contents
4.0 INTERCONNECTION TECHNICAL SPECIFICATIONS AND
REQUIREMENTS 4.1 General Requirements 4.2
Response to Area EPS Abnormal Conditions 4.3
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
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IEEE 1547 Contents

• 4.1 General Requirements
• 4.1.1 Voltage Regulation (Dont!)
• 4.1.2 Integration with Area EPS Grounding
  (Coordinate)
• 4.1.3 Synchronization (lt5 voltage fluctuation,
  no flicker)
• 4.1.4 Distributed Resources on Distribution
  Secondary Grid and Spot Networks
• 4.1.4.1 Distribution Secondary Grid Networks
• 4.1.4.2 Distribution Secondary Spot Networks
• 4.1.5 Inadvertent Energization of the Area EPS
  (Dont!)
• 4.1.6 Monitoring Provisions
• 4.1.7 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)

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IEEE 1547 Contents

• 4.2 Response to Area EPS Abnormal Conditions
• 4.2.1 Area EPS Faults (detect faults, cease to
  energize)
• 4.2.2 Area EPS Reclosing Coordination
  (coordinate)
• 4.2.3 Voltage (lt60V,106V 132V, gt144V)
• 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 Quality
• 4.3.1 Limitation of DC Injection (gt0.5 of rated
  output current)
• 4.3.2 Limitation of Flicker Induced by the DR
  (Dont)
• 4.3.3 Harmonics (IEEE 519)
• 4.4 Islanding
• 4.4.1 Unintentional Islanding (Dont)
• 4.4.2 Intentional Islanding (Dont know)

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IEEE 1547 Contents

• 5.0 INTERCONNECTION TEST SPECIFICATIONS AND
  REQUIREMENTS
• 5.1 Design Test
• 5.1.1 Response to Abnormal Voltage and Frequency
• 5.1.2 Synchronization
• 5.1.3 Interconnect Integrity Test
• 5.1.3.1 Protection From Electromagnetic
  Interference (EMI)
• 5.1.3.2 Surge Withstand Performance
• 5.1.3.3 Paralleling Device
• 5.1.4 Unintentional Islanding
• 5.1.5 Limitation of DC Injection
• 5.1.6 Harmonics
• 5.2 Production Tests

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IEEE 1547 Contents

• 5.3 Interconnection Installation Evaluation
• 5.3.1 Grounding Integration with Area Electric
  Power System
• 5.3.2 Isolation Device
• 5.3.3 Monitoring Provisions
• 5.3.4 Area EPS Faults
• 5.3.5 Area EPS Reclosing Coordination.
• 5.4 Commissioning Tests
• 5.4.1 Unintentional Islanding Functionality Test
• 5.4.1.1 Reverse-Power or Minimum Power Test
• 5.4.1.2 Non-Islanding Functionality Test7
• 5.4.1.3 Other Unintentional Islanding
  Functionality Tests
• 5.4.2 Cease to Energize Functionality Test
• 5.5 Periodic Interconnection Tests

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SCC21 Interconnection Projects
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SCC21 Interconnection Projects
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SCC 21 Contact Information

• Dr. Richard DeBlasio
• email ddeblasi_at_nrel.gov
• voice (303) 275 - 4333
• Mr. Tom S. Basso
• email thomas_basso_at_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/ar
  chives/

NREL 1617 Cole Blvd. MS-1614 Golden, CO
80401-3393 http//www.nrel.gov
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