Net Metering and Utility Interconnection Presented by: Bill Brooks Engineering
Technical Interconnection Issues: Codes and Standards
Who Has a stake in the PV Industry? Million Solar Roofs Partnerships p Electric utility companies p Electric customers wanting to install a PV system p PV component manufacturers p PV equipment and system dealers p Local jurisdictions enforcing building codes p
Why Do We Need PV Codes and Standards? p To facilitate the broad acceptance of the technology among local jurisdictions and interconnecting utilities. p To maintain minimum requirements for PV products and their installation. p To standardize and reduce the cost of testing and certification.
Who sets codes and standards? p National Fire Protection Association (NFPA) • National Electrical Code (NEC) - Electrical Power System Installation--developed in conjunction with electrical trade and industry experts. p Underwriters Laboratory (UL) • Standards for Electrical Equipment Safety--developed in conjunction with manufacturers. p Institute of Electrical and Electronic Engineers (IEEE) • Standards for electrical and electronic equipment-developed in conjunction with applicable industry experts. p 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 p UL Standard 1703, Flat-plate Photovoltaic Modules and Panels p IEEE 929 -2000, Recommended Practice for Utility Interface of Photovoltaic (PV) Systems (approved in p January 2000) p 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? p 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. p 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 p Equipment protection p Service reliability p Power quality p
Utility Interconnection Requirements IEEE standard 929 p UL standard 1741 p Utility practice and requirements p Public utility commission statutes p
UL 1741 Standard for Static Inverters and Charge Controllers for Use in Photovoltaic Power Systems First released in May of 1999 p Has been revised to match IEEE 929 -2000 p Compliance with revised document required on November 7, 2000) p New title reads “Standard for inverters, converters, and controllers for use in Independent Power Systems. ”(Nov 8) p
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. p 1741 incorporates the testing required by IEEE 929 (frequency and voltage limits, power quality, nonislanding inverter testing) p 1741 testing includes design (type) testing and production testing. p 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). p
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 p 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. p Inverter must be acceptable to utility for interconnection. p Utility also may have a list of acceptable manual disconnects to choose from. p Starting January 1, 1999, systems are to be billed on annual basis. p Starting January 1, 2001, systems may elect time-of-use net metering (up to 30% increased financial benefit) p
IEEE 929 -2000 p Passed by IEEE Standards Board in January, 2000. p Represents an excellent primer on PV inverter interconnection issues.
The Need for PV Interconnection Standards l l 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
What Does IEEE 929 Really Impact? Utility System PV Array M Inverter
IEEE 929 Outline Introduction p 1. Overview (scope & purpose) p 2. References p 3. Definitions (inverter, islanding, PCC, quality factor, etc…) p 4. Power quality p 5. Safety and protection functions p Annexes p
Power Quality l Power quality problems in general are rising because of proliferation of non-linear loads on utility systems -all customers suffer l PV should not add to that problem
Power Quality • Power Quality • • 1. 2. 3. 4. • Service Voltage Flicker Frequency Waveform Distortion IEEE 519 • 5. Power Factor
Safety and Protection Functions p 1. Response to Abnormal Utility Conditions ü a. ü b. ü c. ü d. Voltage Disturbances Frequency Disturbances Islanding Protection Reconnect After a Utility Disturbance 2. Direct Current Isolation p 3. Grounding p 4. Manual Disconnect p
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.
Terminology p 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 p Islanding
The PV Inverter as a UPS Some inverters are designed to provide uninterruptible power to critical loads p The power to critical loads is maintained when the connection to the utility is severed p 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 p
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
Manual Disconnect Switch PV Array Local Loads Utility System M Inverter
Islanding Testing
Why do we need testing? p Utility engineers are required to do testing of system protection equipment p 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 p “Typical” island (no balance between load and island) • Trip time - 10 cycles (to avoid interference with reclosing) p “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 p and a Q (quality factor) 2. 5, where Q=R(C/L)½ p 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 p RLC load that has been tuned to 60 Hz p
Sandia Anti-Islanding Method Basic Concepts Frequency and voltage trip points are used p Error signal from frequency and voltage is calculated each ½ cycle p Frequency and voltage are then “tweaked” in the same direction as error signal p If tweaking results in change, then accelerated tweaking results to push frequency or voltage to trip points p
Test Circuit Used at Sandia
“Less Than Sandia” Scheme Balanced load and generation (25% of Capacity)
“Less Than Sandia” Scheme (125% of Inverter Capacity)
“Less Than Sandia” Scheme Balanced load and generation (100% Capacity)
Sample Test-Using Sandia Anti-Islanding Method Note that trip time meets “typical” criteria even though test is with “balanced” conditions
Sample Motor Load Tests—Using Sandia Anti-Islanding Method Required trip time - 2 seconds
Motor Load Tests Generation to load ratio impacts
IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems p Approved at June 2003 IEEE Standards Board Meeting
IEEE Standards Classification 1. Standards: documents with 1. mandatory requirements (shall) 2. Recommended Practices: documents in which 1. procedures and positions preferred 2. 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.
1547 Body of Standards 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems Guide for Networks Guide for Impacts P 1547. 3 Draft Guide for Monitoring, Information Exchange and Control of DR Interconnected with EPS P 1547. 2 Guide For Interconnection System Certification Guide for Islanding & Anti-Islanding 1547. 1 Draft Standard for Draft Conformance Test Application Procedures for Guide for IEEE Equipment P 1547 Draft Interconnecting Standard for Distributed Interconnecting Resources with Distributed Electric Power Resources with DP Specifications Systems Electric Power and Performance Systems The above schematic identifies existing standards development projects and potential future activities under discussion by P 1547 Work Group members.
1547: Interconnection Is The Focus Distributed Resource (DR) unit Interconnection System Area Electric Power System (EPS)
1547 Interconnection Terms
IEEE 1547 Contents INTRODUCTION 1. 0 OVERVIEW 1. 1 Scope 1. 2 Purpose 1. 3 Limitations 2. 0 REFERENCES 3. 0 DEFINITIONS
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.
IEEE 1547 Contents 4. 0 INTERCONNECTION TECHNICAL SPECIFICATIONS AND REQUIREMENTS 4. 1 4. 2 4. 3 4. 4 General Requirements Response to Area EPS Abnormal Conditions Power Quality Islanding 5. 0 INTERCONNECTION TEST SPECIFICATIONS AND REQUIREMENTS 5. 1 5. 2 5. 3 5. 4 5. 5 Design Test Production Tests Interconnection Installation Evaluation Commissioning Tests Periodic Interconnection Tests ANNEX A (INFORMATIVE) BIBLIOGRAPHY
IEEE 1547 Contents 4. 1 General Requirements 4. 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 Networks 4. 1 Distribution Secondary Grid Networks 4. 1. 4. 2 Distribution Secondary Spot Networks 4. 1. 5 Inadvertent Energization of the Area EPS (Don’t!) 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 (C 37. 90. 2) 4. 1. 8. 2 Surge Withstand Performance (C 62. 41 or C 36. 90. 1) 4. 1. 8. 3 Paralleling Device (withstand 220% of rated voltage)
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 (<60 V, 106 V – 132 V, >144 V) 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, C 84. 1 Range B) 4. 3 Power Quality 4. 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 Islanding 4. 4. 1 Unintentional Islanding (Don’t) 4. 4. 2 Intentional Islanding (Don’t know)
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
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 Test 7 5. 4. 1. 3 Other Unintentional Islanding Functionality Tests 5. 4. 2 Cease to Energize Functionality Test 5. 5 Periodic Interconnection Tests
SCC 21 Interconnection Projects 53
SCC 21 Interconnection Projects 54
SCC 21 Contact Information • Dr. Richard De. Blasio email: ddeblasi@nrel. gov voice: (303) 275 - 4333 • Mr. Tom S. Basso email: thomas_basso@nrel. gov voice: (303) 275 - 3753 NREL 1617 Cole Blvd. MS-1614 Golden, CO 80401 -3393 http: //www. nrel. gov • IEEE SCC 21 -- IEEE Standards Coordinating Committee 21 on Fuel Cells, Photovoltaics, Dispersed Generation, & Energy Storage http: //grouper. ieee. org/groups/scc 21/ • P 1547 Draft Standard for Interconnecting Distributed Resources with Electric Power Systems -- web site and archives http: //grouper. ieee. org/groups/scc 21/1547/archives/ 55
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