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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