Photovoltaic Systems James Dunlop, PE
Independent Electrical Contractors West Florida Chapter July 11, 2012 Clearwater, FL
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Solar Photovoltaic (PV) Systems Solar PV systems are electrical generators that produce energy for electrical loads and may interface with other electrical systems.
Power Conditioning Energy Source
PV Array
Inverter
Power Distribution
Electrical Load
Load Center
Energy Conversion
Energy Storage (optional) 2012 Jim Dunlop Solar
Electric Utility
Battery www.JimDunlopSolar.com 2
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PV System Applications Spacecraft
Lighting
Consumer electronics
Calculators, radios and watches
Specialty applications
Rural development
Health care facilities, schools and community centers
Off-grid power
Signs, security and parking areas Transportation, navigation and aviation aids
Lighting and appliances for remote homes and facilities
Telecommunications facilities Grid-connected systems
Agricultural uses
Water pumping and irrigation Fence charging
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Remote monitoring, railway signals, security systems and water treatment
Residential, commercial and utilityscale
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Commercial Rooftops National Electric, Albuquerque, NM
Environmental Protection Agency, Raleigh, NC
National Electric
NREL/EPA
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Commercial Rooftops Convention Center, Orlando, FL Georgia Tech Aquatic Center, Atlanta, GA
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Residential Grid-Connected
FSEC/Lakeland Electric
New Smyrna Beach Utilities Commission
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Residential Grid-Connected
FSEC/Lakeland Electric
Sharp Solar
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Utility-Scale PV Systems Kennedy Space Center, FL – 10 MW
Carissa Plains, CA (c. 1985) – 6 MW
Florida Power and Light
Alamosa, CO – 8.2 MW
SolarWorld/ARCO
NREL/Steve Wilcox
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Utility-Scale Desoto Next Generation Energy Center, Arcadia, FL – 20 MW
Florida Power and Light
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Military Bases Nellis AFB, Las Vegas, NV – 14 MW
SunPower/Bombard Electric
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High-Tech Centers Google, Mountain View, CA – 1.6 MW
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Commercial Roofs Habilitation Center, Portland, OR
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Airports
Dennis Whalen
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The PV Industry: Yesterday and Today c. 1990
c. 2010
Installed Capacity
< 50 MW/yr worldwide
> 10 GW/yr worldwide > 500 MW/yr in U.S.
Product Listing and Certification
Infancy
All modules, inverters, controls and combiners listed to UL standards
Code Compliance
PV first introduced in 1984 NEC Few systems permitted and inspected
All systems permitted and inspected by building officials
System Voltage
Residential ≤ 48 VDC
Residential up to 600 VDC Commercial up to 1000 VDC
Predominant Markets
Stand-alone, off-grid
Grid-connected residential, commercial and utility-scale
Number of PV Companies
Hundreds
Tens of thousands
Maximum System Size
10 to 100 kW
1 to 20+ MW
Utility Interconnection
Few utilities permitted PV interconnections
All states and utilities permit interconnections from 2 to 20 MW
Licensing and Personal Certification
Nonexistent
State licensing and national certification programs emerging
Contractors and Installers
Small specialized companies, diversified in solar thermal and PV
Larger companies, electrical contractors and project developers
Global PV Industry Revenue
Tens of millions
Tens of billions
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Market Drivers Increasing costs and dependence on imported energy Environmental impacts from fossil fuel use Electric utility restructuring Net metering and interconnection rules Legislative mandates for renewable generation Financial incentives Increasing public awareness and interest
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Financial Incentives Rebates Tax credits and exemptions Production incentives Grants and loans
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Database of State Incentives for Renewable Energy (DSIRE) National resource for PV project developers and consumers:
www.dsireusa.org
Contains information on rules, regulations and policies for renewable energy and energy efficiency programs in all states, including:
Financial incentives Net metering and interconnection rules Licensing, permitting and building codes Legislative actions Interstate Renewable Energy Council/North Carolina Solar Center
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PV Project Development PV installation projects involve the following steps:
Marketing, sales and customer development Site survey and preplanning Pursue financing and incentives System design and engineering Equipment specification and procurement Plan review and permitting Interconnection application and approval Contracting and installation Commissioning, inspection and approval Operations, maintenance and performance monitoring
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Site Assessment An initial assessment for a PV installation involves gathering information to determine the project requirements. Customer development:
Discuss needs and expectations Complete sales, contracting and financing
Site conditions:
Solar resource and environmental factors Verify electric energy consumption and costs Use satellite imagery and mapping tools
Installation preplanning:
Array location and structural support Hazard assessment Design and plan review Electrical, fire, safety and building codes Equipment and manpower needs
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PV System Documentation A complete documentation package for PV system installations should include:
System design and equipment specifications Owner/operator manuals for the system and major components Electrical and mechanical drawings Site layout and equipment locations Installation and commissioning procedures Operating and maintenance procedures
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Types of PV Systems Stand-Alone Systems
Operate autonomously off-grid. Typically use batteries for energy storage. Sizing is based on electrical loads and desired storage period.
Interactive Systems
Operate in parallel with the electric utility grid. Intended to supplement site energy use independent of loads. Do not generally use batteries or provide backup for utility power.
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Stand-Alone PV Systems with Charge and Load Control This controller protects battery from overcharge
PV Array
This controller protects battery from overdischarge
Charge Controller
Load Controller
DC Load
Battery
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Stand-Alone PV Systems with AC Loads PV Array
Charge Controller
DC Load
Battery
Inverter/ Charger
AC Load
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AC Source (to Charger Only)
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Utility-Interactive PV System
AC Loads
PV Array
Inverter
Load Center
Electric Utility 2012 Jim Dunlop Solar
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Utility-Interactive PV System with Energy Storage Backup AC Loads
Primary AC Loads
Bypass circuit
Critical Load Sub Panel
Inverter/ Charger
Main Panel
AC Out
AC In DC In/out
Charge Control
PV Array
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Battery
Electric Utility
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Major System Components Photovoltaic (PV) Array
An assembly of PV modules that convert sunlight to DC electricity.
Power Conditioning Equipment
Inverters, chargers and controllers that process DC power from PV arrays and produce AC power for utilization loads.
Energy Storage
Batteries store energy produced by PV arrays, and are used in most stand-alone systems, but only in specially-designed grid-tied systems.
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PV System Components
1
2
5
1. PV modules and array 2. Combiner box 6
4
3. DC disconnect 4. Inverter (charger & controller) 5. AC disconnect
3
6. Utility service panel 7
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7. Battery (optional)
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Balance-of-System Components Balance-of-System (BOS) Components
Mechanical or electrical equipment and hardware used to assemble and integrate major components, and to conduct, distribute and control the flow of power in the system.
Examples of BOS components include:
Conductors (wiring) Raceways (conduit) Junction and combiner boxes Disconnect switches Fuses and circuit breakers Terminals and connectors Array mounting hardware
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Silicon Solar Cells Silicon solar cells produce about 0.5 to 0.6 volt independent of cell area, depending on temperature. The current output of a solar cell depends primarily on the cell area, its efficiency, and the incident solar radiation. Modern silicon solar cells are up to 8 inches in diameter and produce up to 4 watts and 8 amps under full sunlight.
Monocrystalline cell
Polycrystalline cell
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PV Modules and Arrays PV modules produce DC power and are assembled electrically and mechanically to form an integrated power supply. An array is the total DC power generating unit designed to produce a specified electrical output. PV Module
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PV Array
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Photovoltaic Arrays PV arrays are constructed from building blocks of individual PV modules, panels and subarrays that form a mechanically and electrically integrated DC power generation unit.
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Photovoltaic Arrays
Ground-mounted rack array
Pole-mounted tracking array
Standoff roof-mounted array Building-integrated array 2012 Jim Dunlop Solar
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Utility-Interactive Inverters Interactive inverters use PV arrays for DC power input, and supply synchronized AC output power in parallel with the utility grid. Site AC loads may be served by the inverter output, utility or both. Excess power not needed by local loads flows to the grid.
Power ratings limit the size of the connected PV array; output is independent of loads.
All listed interactive inverters produce utility-grade sine wave output and include anti-islanding safety features to de-energize inverter output to the grid upon loss of grid voltage.
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Types of Interactive Inverters Module-Level Inverters
200-300 W, includes AC modules and micro inverters integral to or installed at the PV module level.
String Inverters
2-12 kW, designed for residential and small commercial applications using 1-6 series-connected PV array source circuits.
Central Inverters
30-50 kW up to 500 kW, designed for commercial applications with homogeneous arrays.
Utility-Scale Inverters
500 kW to 1 MW, designed for solar farms.
Bimodal Inverters
2-10 kW, battery-based interactive inverters that provide grid backup to critical loads.
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Module-Level Inverters AC modules are factoryintegrated PV modules with interactive inverters. Micro inverters are similar in concept but are separate equipment. Typically 200-300 W rated maximum AC output (approx. PV module size).
Enphase Micro Inverter
Used primarily for residential and small commercial applications, and can achieve greater energy harvest from partially shaded and multidirectional arrays. 2012 Jim Dunlop Solar
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String Inverters String inverters are small inverters in the 1 to 12 kW size range, intended for residential and small commercial applications.
Generally single-phase, usually limited to 1 to 6 parallel-connected source circuits, or “strings”. Some integrate source circuit combiners, fuses and disconnects into a single unit.
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Central Inverters Central inverters start at 30-50 kW up to 500 kW, and interconnect to 3-phase grids.
Best suited for homogeneous PV arrays having all the same modules and source circuit configurations, and aligned and oriented in the same direction with no shading.
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Utility-Scale Inverters Most commercial PV inverters up to 500 kW installed on public and private properties are interconnected to the grid at service voltages less than 600 VAC.
These systems must comply with NEC requirements and use listed inverters and other equipment. PV arrays are less than 600 VDC.
Large inverters 500 kW to 1 MW and higher used in PV power plant installations are interconnected to the grid at distribution voltages up to 38 kV.
For utility-controlled sites, certain variances with the NEC and product listing requirements may apply.
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Utility-Scale Inverters Utility-scale inverters use higher DC input and AC output voltages to reduce losses, and the size and costs of the conductors and switchgear required.
DC input from PV arrays 900 to 1000 VDC AC output to grid at distribution level voltages up to 35 kV.
Packaged systems include inverters, transformers, switchgear, climate-controlled enclosure and mounting platform as a pre-engineered unit. 2012 Jim Dunlop Solar
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Bimodal Inverters Bimodal inverters use batteries for DC power input and may operate in either interactive or stand-alone mode. In interactive mode, the inverter produces AC power output in proportion to PV array production, while maintaining a prescribed maximum battery voltage. Upon loss of grid voltage, the inverter automatically transfers to stand-alone mode, and powers backup loads isolated from grid. Bimodal inverters may also include load control, battery charging, and generator starting functions. 2012 Jim Dunlop Solar
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PV Systems and the National Electrical Code Article 690 Solar Photovoltaic Systems
Addresses safety standards for the installation of PV systems.
Many articles in the first four chapters of the NEC also apply to most PV installations, including but not limited to:
Article 110 Article 230 Article 240 Article 250 Article 300 Article 310 Article 705
Requirements for Electrical Installations Services Overcurrent Protection Grounding and Bonding Wiring Methods Conductors for General Wiring Interconnected Electric Power Production Sources
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NEC Article 690: Solar Photovoltaic Systems Article 690 Solar Photovoltaic Systems includes nine parts addressing the following areas of PV installations: I. General II. Circuit Requirements III. Disconnecting Means IV. Wiring Methods V. Grounding VI. Marking VII. Connection to Other Sources VIII. Storage Batteries IX. Systems Over 600 Volts
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Photovoltaic Power Source The PV power source consists of the complete PV array DC power generating unit, including PV source circuits, PV output circuits, and overcurrent protection devices as required. Photovoltaic Power Source PV Source Circuits
PV Array
PV Module
PV Output Circuit
To disconnect means and DC equipment
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Interactive PV System Components and Circuits Interactive System PV Source Circuits
PV Output Circuit
Inverter Input Circuit
Source Circuit Combiner Box
Inverter Output Circuit AC Fused Disconnect
Ground Fault Protection
Inverter
Utility Disconnect
Main Service Panel
DC Fused Disconnect
PV Array
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Integral components in many small string inverters < 12 kW
Electric Utility
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Stand-Alone PV System Components and Circuits Stand-Alone System
DC Loads
PV Source Circuits
Inverter DC input Circuit
PV Output Circuit Source Circuit Combiner Box
AC Loads
Ground Fault Protection
Inverter Output Circuit
Inverter Fused Disconnect
Inverter/ Charger PV Fused Disconnect
Charge Controller
PV Array
Battery Fused Disconnect
Auxiliary AC Source Battery
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Circuit Requirements The conductors, overcurrent devices, disconnect means and other equipment used in PV system circuits are selected and sized based on the maximum circuit voltages and currents. Specifications and ratings for major components, including PV modules and inverters, are required to determine the appropriate circuit parameters for sizing the conductors and wiring systems.
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Utility Interconnection 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.
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Point of Interconnection Interactive inverters may be connected to either the load side or the supply side of the service disconnecting means [690.64, 705.12].
To Utility Supply Side Load Side
Distribution Equipment
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Service Disconnect
To Branch Circuits
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Supply Side Connection To Utility
Interactive Inverter
Service Disconnect
Service Rated Fused Disconnect
To Branch Circuits
Distribution Equipment
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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 Service Disconnect Backfed Circuit Breaker
200 A
To Branch Circuits Interactive Inverter 40 A
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Distribution Equipment www.JimDunlopSolar.com 50
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Permitting Guide A useful resource for contractors and building officials. Covers recommended plan review and permitting guidelines for small PV systems.
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Permit Applications Minimum requirements for PV system permits should include:
Electrical diagrams detailing all equipment and BOS components, including conductors, raceways, connections, disconnects, overcurrent protection and grounding. Mechanical drawings showing details and hardware for the attachment and weathersealing of PV array mounting structures to buildings. Site diagrams or surveys showing location property lines, easements, structures, PV system equipment and electrical services. Specifications and ratings for entire system and manuals for all major components. Code calculations for electrical and mechanical designs
Engineering approvals may be required on commercial projects and for structural evaluations in some jurisdictions. 2012 Jim Dunlop Solar
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Plan Review A plan review typically considers the following items:
Equipment is listed, labeled and appropriate for the conditions of use. Conductors, raceways and supports are properly sized, rated and located. Disconnects and overcurrent protection devices are properly rated and located. System grounding and bonding methods and materials are clearly specified, identified and located. Connections to other electrical systems are compatible with the services and distribution equipment using approved methods. The methods and materials for mounting the PV array are structurally sound and weathersealed as appropriate.
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Field Inspection Guidelines A guide for inspecting gridconnected PV systems including checklists and common code violations.
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Field Inspection The field inspection process verifies compliance of PV installations in accordance with approved plans, as-built modifications and code requirements.
Use checklists to organize and stage the inspection process.
Use site diagrams and PV system drawings approved for permitting with as-built changes.
Contractor should be present and facilitate inspection access by providing ladders, lifts, etc. as required.
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Suggested References
Photovoltaic Systems, 2007, by Jim Dunlop. ISBN 978-0-8269-1287-9, National Joint Apprenticeship and Training Committee and American Technical Publishers: www.jimdunlopsolar.com
National Electrical Code, National Fire Protection Association. www.nfpa.com
OSHA Safety Standards for the Construction Industry, www.osha.gov
Photovoltaic Systems Engineering, 3rd Edition, by Roger Messenger and Jerry Ventre. ISBN 0-8493-1793-2, CRC Press LLC: www.crcpress.com
Photovoltaic Power Systems and the National Electrical Code: Suggested Practices, February 2005, by John Wiles. SAND2005-0342, New Mexico State University/Southwest Technology Development Institute and Sandia National Laboratories: www.sandia.gov/pv
Roofing Construction and Estimating, 6th Printing, 2006. ISBN 978-1-57218-007-9, Craftsman Book Company: www.craftsman-book.com
Soares Book on Grounding and Bonding, 10th Edition, 2008, ISBN 1-890659-47-9. International Association of Electrical Inspectors: www.iaei.org
Battery Service Manual, 12th Edition, Battery Council International: www.batterycouncil.org
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Suggested References
Maintenance and Operation of Stand-Alone Photovoltaic Systems, Sandia National Laboratories: www.sandia.gov/pv/docs/PDF/98TLREF13.pdf
Solar America Board for Codes and Standards: www.solarabcs.org
National Renewable Energy Laboratory Website: www.nrel.gov
Sandia National Laboratories Photovoltaics Website: www.photovoltaics.sandia.gov/
Southwest Technology Development Institute, PV Codes and Standards Website by John Wiles: www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/Codes-Stds.html
Interstate Renewable Energy Council Website: www.irecusa.org
IAEI News, International Association of Electrical Inspectors, www.magazine.iaei.org
PHOTON International Magazine : www.photon-magazine.com/
Solar Pro Magazine: www.solarprofessional.com
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Questions and Discussion
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