1. Integrating PV on Distribution
Forrest Small
Director, Energy Practice
Navigant
April 2011
ENERGY

2. Discussion Points
Points to discuss today
» Distributed PV increasing
» Effects of high penetrations of distributed PV
» Energy storage and distributed PV
©2011 Navigant Consulting, Inc. 1
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3. Growing PV Installed Base
PV installations are increasing dramatically, and could soon exceed
annual wind installations.
Annual Renewable Energy Capacity Additions (MW per year)
12,000
10,000
Hydro
8,000 Geothermal
6,000 Landfill Gas
Biomass
4,000
Solar
2,000
Wind
0
2010 2011 2012 2013 2014 2015
Forecasts assume: no renewal of existing federal tax credits after their current expiration dates;
and no new federal stimulus program is created.
Source: Navigant Consulting, Inc., January 2009. Note: Solar includes solar PV and CSP; Biomass includes biomass co-firing.
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4. Solar Ownership by Utilities
A growing number of utilities want to install distributed solar on a
large scale and put it in ratebase.
Utility Programs for Distributed PV: Examples of Filings for Rate Basing
Filed February 2010 Filed June 2008
Filed February 2009 3 MW 20MW in 2 years, Proposed 4Q 2008
500MW in 5 years3 Modified to 10 MW 5MW
Filed February 2009
120MW in 5 years
Filed March 2008
250MW in 5 years,
Modified to 500 MW3
Filed November 2007
3.5MW in 5 years2
A Sempra Energy Utility
Filed January 2010 Filed May 2008
Filed July 2008 Filed May 2009 80 MW 35MW Program
77MW in 4 years1 1.5 MW
Additional Utility Programs; 3rd party or community owned
Sacramento Municipal Utility District (1MW) , Portland General
Notes:
Electric (>2MW), Hawaii Electric Company (16 MW), City of
1. SDG&E: 55MW owned by utility
Ellensburg (<1 MW), City of St. George (<1 MW)
2. ACE: 0.5MW will be utility owned and located on utility facilities.
3. PG&E and SCE 50% ownership
©2011 Navigant Consulting, Inc. 3
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5. Connecting PV on Distribution
PV can be connected at three levels in the distribution system
depending on the location and size of the installation.
Distributed PV can by interconnected Substation interconnection assumes that the
at three levels PV is physically located close to the
substation, and a dedicated electrical
connection to the low side bus would be
Substation made.
PV
Primary Distribution interconnection
assumes that the PV is connected directly to
PV the distribution system, and is not
integrated with a customer’s electrical
Dedicated system.
Distribution Metering
Circuits
Behind the Meter interconnection assumes
PV the PV is integrated with a customer’s
Net
electrical system, and either net metering or
Metering dedicated metering could be employed.
“Behind the meter”
Each point has a practical limit based on the impact of the PV on the
distribution system.
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6. Challenges of High PV Penetration
In addition to high cost, T&D concerns, communications, and
regulatory challenges have limited the PV deployed.
Challenges of High PV Penetration
Voltage regulation (D)
Transmission and Reverse power flow (D)
Distribution Concerns Power fluctuation/frequency regulation (T)
Harmonics (D)
Lack of communications throughout the distribution
system
Inverter operating limits (e.g., IEEE 1547)
Communications
Limited ability to forecast PV resource for capacity
planning
Non-standard communications protocols
Unstructured interconnection standards and ownership
Regulatory and control in some states
Business Models
Lack of rate recovery and PV-“friendly” tariffs
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7. Transmission and Distribution Performance Concerns
Past research had indicated that distribution performance concerns if
PV exceeded certain penetrations.
Recommended Limitations on PV Penetration Based On T&D Performance Concerns
Recommendation
T&D
for Maximum PV
Performance Description of Impact
Penetration on
Concerns
Circuit Peak Load
Adequate voltage regulation may be difficult due to changes in
Voltage circuit load and power flow while PV is producing. Also of
< 40%
Regulation concern is voltage depression after a circuit restoration, when
load is restored but PV systems have not come back online.
Changes in PV output can cause the power flow on
Reverse
distribution circuits to vary, and in some high generation/low 5% to 30%
Power Flow
load cases, the flow could reverse.
The variability of PV output due to cloud transients has been
Power shown to create power fluctuations, and may be incompatible
Fluctuation/ with the ramp rates of some central station generation. This
5% to 30%
Frequency variability may require higher levels of system frequency
Regulation regulation, increasing the cost of accommodating higher
penetrations of PV.
Source: Distributed Photovoltaic Systems Design and Technology Requirements, C. Whitaker, J. Newmiller, M. Ropp, and B. Norris, February
2008, and Navigant analysis, 2008.
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8. Power Quality Concerns
As PV penetration increases, harmonics may become an issue that must
be evaluated case by case.
Effects of Harmonics and Limitations on PV Penetration
Study Country Summary of Findings
Germany (1) TV loads coupled w/ PV created higher distortion
Australia (2) Limit found at ~ 18% penetration
Denmark (3) Up to 30%; TV distortion > PV
Japan (3) Line-end over-voltages on cluster of 550 houses
Australia (3) 665 homes connected with no significant impacts
Sources
1. Distributed Energy Resources and Waveform Distortion, Math Bollen, Christine Schwaegerl, and Sebastian Schmitt
2. Harmonic Impact of Residential Type Photovoltaic Inverters on 11kV Distribution System, A.A. Latheef, V.J. Gosbell, & V. Smith
3. The Effects of Harmonics Produced by Grid Connected Photovoltaic Systems on Electrical Networks, Abdulvahid Çelebi & Metin
Çolak
•In some studies non-linear loads in residences (e.g., televisions)
had a greater impact on harmonics than PV inverters.
•Distribution circuits with strong sources, shorter length and higher
voltages tended to be less susceptible to excessive distortion.
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9. Results From Recent Work » Navigant
Recent studies show that distribution voltage stays within system
design criteria even with high penetrations of PV…
On some circuits PV penetration as high as
30% does not exceed voltage limits
1.040
1.030
1.020
Peak Load PV Bus
1.010 Voltage
Low Load PV Bus
1.000 Voltage within +/- 3% Voltage
Voltage
0.990
Peak Load Minimum
0.980 Feeder Voltage
Low Load Minimum
0.970
Feeder Voltage
0.960 Peak Load Maximum
Voltage Drop
0.950
0.940
1% 9% 15% 30%
DG Pentration
Source: Navigant, Analysis of southwest investor owned utility, November 2010.
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10. Results From Recent Work » Natural Resources Canada
… even when the PV is located far from a substation.
High PV penetration may not exceed voltage limits,
even far from the substation
Source: Natural Resources Canada. Integration of Photovoltaic Power Systems in High-Penetration Clusters for Distribution Networks and
Mini-Grids, 2009.
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11. Results From Recent Work » NREL
Monitoring conducted by NREL showed no adverse conditions
occurred even in a high penetration solar community.
Results with Penetrations of 11-13%
• No excessive service or
substation voltage due to reverse
power flow
• Cloud transients did not
Source: SunPower adversely affect the distribution
system
• Anatolia SolarSmartSM Homes • No indication that utility voltage
Community, Rancho Cordova, CA transients (capacitor switching)
• Highly energy efficient homes with caused PV systems to trip off-
integrated PV systems line
• 2 kW grid-connected PV systems
with remotely monitored inverters
Source: National Renewable Energy Laboratory. Impact of SolarSmart
Subdivisions on SMUD’s Distribution System, July 2009.
©2011 Navigant Consulting, Inc. 10
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12. Grid Benefits from PV?
Smart Grid could support better integration of distributed resources
and the utility distribution system, and provide grid benefits.
AMI facilitates communications
between utility information
systems and PV inverters
Information Flow
Inverter
Power Electrical Utility
Smart
Service AMI Information
Control Meter
Panel Systems
Operator Interface
Power Flow
Load Utility
Energy Storage Circuits DA Distribution
(ES) System
DA helps manage
Demand DR curtails small amounts
ES provides input to circuit voltage and
Response of customer load for short
inverter to compensate for accommodate changing
(DR) periods of time (<2 hrs)
PV variability (<8 hrs) power flow
PV system Smart Grid plus DR and ES Functionality Electrical System Components
©2011 Navigant Consulting, Inc. 11
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13. Recap
Recap
» Distributed PV will become a significant energy resource in utility
systems.
» Distribution effects from high penetrations of PV may not be as
significant as once thought.
» Smart Grid and integrated PV-storage could provide grid benefits.
©2011 Navigant Consulting, Inc. 12
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14. Key
CONTACTS
Forrest Small
Director
Burlington, MA
(781) 270-8303
Forrest.Small@navigant.com
©2010 Navigant Consulting, Inc.
©2011 13
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