Low Cost Plug and Play Solar Photovoltaics for Residential
Households Dr. David Lubkeman
FREEDM Systems Center
North Carolina State University
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Acknowledgement
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Acknowledgment: “This material is based upon work supported by the Department of
Energy under Award Number DE-EE0006036.”
Disclaimer: “This report was prepared as an account of work sponsored by an agency of
the United States Government. Neither the United States Government nor any agency
thereof, nor any of their employees, makes any warranty, express or implied, or assumes
any legal liability or responsibility for the accuracy, completeness, or usefulness of any
information, apparatus, product, or process disclosed, or represents that its use would
not infringe privately owned rights. Reference herein to any specific commercial product,
process, or service by trade name, trademark, manufacturer, or otherwise does not
necessarily constitute or imply its endorsement, recommendation, or favoring by the
United States Government or any agency thereof. The views and opinions of authors
expressed herein do not necessarily state or reflect those of the United States
Government or any agency thereof.”
Outline
• Residential PV System Installation Trends
• Plug and Play (PnP) Initiative
• PnP General Requirements
• NCSU PnP System
• Future Work
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PV Installation Trends
• Increase in PV Installations over past 3 years for both Utility and Residential scale.
• Not shown, but Residential installs surpassed Commercial in Q1 2014.
4
Source: http://www.seia.org/research-resources/solar-industry-data
852
1919
3369
4751
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
2010 2011 2012 2013
Inst
alla
tio
n (
MW
dc)
PV Installations by Market Segment, 2010-2013
Residential Non-Residential Utility
PV System Pricing Trends
5
3.85
2.9
2.14 1.85
6.39
5.89
4.91 4.56
0
1
2
3
4
5
6
7
Q1 2011 Q1 2012 Q1 2013 Q1 2014
Inst
alle
d P
rice
($
/Wd
c)
Average Installed Price by Market Segment Q1 2011-Q1 2014
Utility Residential
• Utility PV system price declined by nearly 50% since 2011.
• Residential PV system price declined by about 30% in same time period.
Cost Breakdown for Residential PV • Soft costs are
substantial percentage of residential system cost.
• Soft cost includes sales tax, supply chain, installer profit, indirect costs.
• SunShot goal to substantially reduce soft costs.
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Source: Benchmarking of Non-Hardware Balance-of-System (Soft) Costs for U.S. Photovoltaic Systems,
Using a Bottom-Up Approach and Installer Survey, NREL/TP-6A20-60412
$6.60
$5.22
$1.50
0
1
2
3
4
5
6
7
2010 2012 SunShot 2020Target
Syst
em
Co
st (
$/W
)
Total PV system price and SunShot target for 5kW residential PV
Other Soft Costs
Permitting,inspection, andinterconnectionInstallationLabor
CustomerAcquisition
Residential PV System Layouts
• PV panels connected to racking systems involving roof penetrations.
• AC or DC wiring from roof to service panel.
• Addition of circuit to existing service panel.
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Central Inverter
Micro Inverter
Plug and Play PV Reduce “soft costs” by designing:
• Simple mechanism for attaching PV panels to roof, preferably avoiding roof penetrations. Lightweight roof modules.
• DC and AC wiring connections made by plug and play cable kits.
• System interconnects to household service similar to an appliance plugin without modifying household wiring.
• Elimination of need for AHJ Inspection.
• Automation of Utility Interconnection.
• Enhanced Safety Features.
Metrics are $/Wdc, Time to acquire, Time to install, Skill level of installers
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Code Requirements
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Category Requirement
Equipment
Specifications
Proper listings for all DC and AC equipment
and connection boxes
CablingAdequate wire size and weather-rated
insulation
ProtectionProper listings and ratings for DC and AC
overcurrent protection
Protection AC and DC ground fault protection
ProtectionDC Arc Fault Detection for voltages of 80 V or
greater
OperationsRapid shutdown, AC and DC systems de-
energized on demand
AHJ Permit & Inspection Requirements
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Category Requirement
Plans Site Plan, One-Line Diagram, Attachment Details
ListingsPV panels listed to UL Standards, Inverters listed to
UL Standards
InstallationInstalled system (equipment, wiring, location, etc.)
matches approved plans
CablingProper cable routing, cable protection, use of strain
reliefs and attachment at minimal intervals
GroundingEquipment (modules, inverter, racking) grounded
in accordance with manufacturer instructions
Signs and
Labels
Proper markings on disconnects, conduits,
raceways, etc
Interconnection Requirements
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Category Requirement
PlansSystem built to AHJ approved
requirements
System Location,
Size and
Configuration
Relevant data provided to utility
ProtectionIEEE 1547 Compliant Anti-Islanding
Protection
Protection AC Current Limiting
Grid-Tie
Screens for interconnection passed:
Feeder DG limit, customer transformer
capacity, customer service capacity
Installation Requirements
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Category Requirement
Installation Lightwide modules easily carried up to roof
WiringNo field wiring required, system plugs in like
an appliance
ConfigurationSystem self configures once all modules are
interconnected together
Commissioning
System preforms self-diagnostics, produces
report and does not operate if diagnostics fail
and a fault condition is detected
New Plug and Play Features
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Feature Category Present Systems Plug and Play System
Power ElectronicsSingle inverter connected to
high-voltage dc sourceMulti-Port Inverter Building Blocks
Switch/Fuse Holders Separate switch/fuse boxesIntegrated into building block
structure
StandardsUL approved individual
componentsUL approved subsystems
Household ConnectionModification of household
wiring
Installation of external plug-in port for
PV System
InspectionOn-site Inspection needed to
verify system wired properly
Self-diagnostics used to verify system
wired correctly and safefly
Utility Interconnection
Maximum Peak Power
Tracking (MPPT) compliant
to existing IEEE 1547
standard
New grid friendly functionality for
voltage control and event ride-
through
NCSU PnP Demonstration System
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Grid
PnP Compliant PV System PV Utility Interface (PUI)
Parallel Connection Option
MPBB
Auto-Commission Logic
Inverter Interface
Communications Interface
Auto-Interconnect Logic
PV Metering
Utility
AHJ
MPBB to PUI
Wiring
Localized
Signaling for
Diagnostics
Permit &
Interconnection
Certificate
(Optional)
Commission/Interconnect
Report
PV
PV
PV
PV
Meter
Meter
Base
PV Plug
Power Conversion Options
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String PV Inverter system
PV Microinverter System
Multi-Port Building Blocks
• Lowest cost per Watt, Simplest Wiring • MPPT Issues, DC Arc Concern
• Best flexibility, No DC arc issue, No MPPT issue • Cost concern
• Better cost per Watt • Simple wiring • No MPPT issue • No DC arc concern
Options Currently Deployed
PUI
PUI
PUI
Photovoltaic Utility Interface
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• Inserted between Meter Socket and Meter.
• Special Connector with Mechanical Interlock.
• Electronic Disconnect.
• Processor for Hosting Logic.
• Ground Fault Protection.
• Power Line Carrier interface to MPBBs.
Residential Home Installation
• Utility or Contractor installed PUI.
• MPBB mounted in power strip connects 4 – 8 PV Panels.
• Standardized Module to Plug Cabling.
• Plug Interlocking with PUI.
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Next Steps
• Solicit Feedback from Utilities and AHJs regarding PnP Requirements and Features.
• Multi-Port Building Block Prototyping.
• Commissioning and Interconnection Hardware and Software for PUI.
• Working Demonstration System.
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