This document summarizes an approach to proactively analyze the impacts of high photovoltaic (PV) penetration on distribution systems. The analysis is conducted using the SynerGEE software to model different PV penetration scenarios on distribution feeders. Various technical criteria are evaluated, such as voltage levels, thermal loading, and impacts to voltage regulation devices. Potential mitigation measures for any issues identified are also modeled and compared, including energy storage, PV output curtailment, and advanced inverter functions. The goal of this proactive approach is to help streamline the PV interconnection process and distribution system planning for high levels of distributed energy resources.

1. DNV GL © 2013 May 6th 2014 SAFER, SMARTER, GREENERDNV GL © 2013
May 6th 2014
Jonathan Flinn
Pro-Active, High Penetration PV Analysis
on Distribution Systems
1
PV Distribution System Modeling Workshop
Santa Clara, CA

2. DNV GL © 2013 May 6th 2014
Contents
 Introduction
 Objectives of Analyses
 Overview of Approach
 Technical Criteria
 Analysis in SynerGEE
 Modeling Advanced Inverter Functions in SynerGEE
 Conclusion
2

3. DNV GL © 2013 May 6th 2014
Introduction – DNV GL
 Merger of brands, consolidation of experience and expertise
3

4. DNV GL © 2013 May 6th 2014
An energy technology powerhouse
4
Offshore wind
Strong expertise in offshore
wind, its support vessels and
connection to the electricity grid
Innovation
Strategic research in energy
storage, smart grids and super
grids; developments of new
standards through joint industry
projects
Testing
Global leader in testing,
inspecting and certifying high-
power and renewable energy
equipment with world class
laboratories
Expert advice
In onshore and offshore wind
power, solar, smart grids, super
grids, infrastructure resilience,
energy markets, regulations and
use
Power player
A strong player across the value
chain: renewable and
conventional power generation,
transmission & distribution and
sustainable energy use

5. DNV GL © 2013 May 6th 2014
Introduction – Jonathan Flinn
 MEng Mechanical Engineering with Aeronautics, University of Strathclyde, 2004
 MSc Safety, Risk and Reliability Engineering, Heriot-Watt University, 2005
 9 years in DNV GL
 Worked with pipelines, wind energy, arctic operations, wave and tidal energy
 Worked in transmission and distribution since 2011
5

6. DNV GL © 2013 May 6th 2014
Introduction – Pro-Active Approach
 Developed in co-operation with HECO
 Aim to streamline PV interconnection process
 Objectives:
– Improve PV interconnection process
– Identify limits on a circuit-specific basis
– Facilitate efficient network planning
– Identification of limits in advance
– Identify existing risks
– Compare limits with existing PV penetrations
– Identify future limits to PV integration
– Run hypothetical future PV scenarios up to high PV penetrations
– Identify appropriate mitigation measures
– Developed from list of potential mitigation measures
6

7. DNV GL © 2013 May 6th 2014
CA Rule 21
7
Complete application received
Screen 1: Connection to distribution system?
Screen 2: Connection to network
Screen 3: Export power causes reverse flow at
voltage regulation devices
Screen 4: Is the aggregate generating facility on
the line section <=15% of line section peak load
Screen 5: Is voltage flicker and/or voltage drop
due to project within IEEE 519 limits
Screen 6: DG <= 10kW
Screen 7: Inverter-based DG <= 250kW
meets IEEE 1547 & UL 1741
Screen 8: SCCR within acceptable limits
Screen 9: Interconnection compatible with line
configuration
Perform
Supplemental Review
Does not qualify for
interconnection under Rule
21
Does supplemental
review determine
requirements?
Company provides the
cost estimate and
schedule for IRS to
determine requirements
Generating Facility
qualifies for
interconnection subject
to requirements, if any,
determined by
supplemental review
Generating
Facility qualifies
for Simplified
Interconnection
no
no
no
yes
yes
no
no
yes
yes
yes
yes
no
no
no
no
yes
yes
yes
yes no

8. DNV GL © 2013 May 6th 2014
CA Rule 21
8
Complete application received
Screen 1: Connection to distribution system?
Screen 2: Connection to network
Screen 3: Export power causes reverse flow at
voltage regulation devices
Screen 4: Is the aggregate generating facility on
the line section <=15% of line section peak load
Screen 5: Is voltage flicker and/or voltage drop
due to project within IEEE 519 limits
Screen 6: DG <= 10kW
Screen 7: Inverter-based DG <= 250kW
meets IEEE 1547 & UL 1741
Screen 8: SCCR within acceptable limits
Screen 9: Interconnection compatible with line
configuration
Perform
Supplemental Review
Does not qualify for
interconnection under Rule
21
Does supplemental
review determine
requirements?
Company provides the
cost estimate and
schedule for IRS to
determine requirements
Generating Facility
qualifies for
interconnection subject
to requirements, if any,
determined by
supplemental review
Generating
Facility qualifies
for Simplified
Interconnection
no
no
no
yes
yes
no
no
yes
yes
yes
yes
no
no
no
no
yes
yes
yes
yes no
Pro-active approach identifies at
which PV penetrations this will occur
for each feeder/transformer

9. DNV GL © 2013 May 6th 2014
CA Rule 21
9
Complete application received
Screen 1: Connection to distribution system?
Screen 2: Connection to network
Screen 3: Export power causes reverse flow at
voltage regulation devices
Screen 4: Is the aggregate generating facility on
the line section <=15% of line section peak load
Screen 5: Is voltage flicker and/or voltage drop
due to project within IEEE 519 limits
Screen 6: DG <= 10kW
Screen 7: Inverter-based DG <= 250kW
meets IEEE 1547 & UL 1741
Screen 8: SCCR within acceptable limits
Screen 9: Interconnection compatible with line
configuration
Perform
Supplemental Review
Does not qualify for
interconnection under Rule
21
Does supplemental
review determine
requirements?
Company provides the
cost estimate and
schedule for IRS to
determine requirements
Generating Facility
qualifies for
interconnection subject
to requirements, if any,
determined by
supplemental review
Generating
Facility qualifies
for Simplified
Interconnection
no
no
no
yes
yes
no
no
yes
yes
yes
yes
no
no
no
no
yes
yes
yes
yes no
Pro-active approach identifies
specific limitations for each
feeder/cluster due to different
criteria (thermal loading, voltage
violations, etc.),

10. DNV GL © 2013 May 6th 2014
CA Rule 21
10
Complete application received
Screen 1: Connection to distribution system?
Screen 2: Connection to network
Screen 3: Export power causes reverse flow at
voltage regulation devices
Screen 4: Is the aggregate generating facility on
the line section <=15% of line section peak load
Screen 5: Is voltage flicker and/or voltage drop
due to project within IEEE 519 limits
Screen 6: DG <= 10kW
Screen 7: Inverter-based DG <= 250kW
meets IEEE 1547 & UL 1741
Screen 8: SCCR within acceptable limits
Screen 9: Interconnection compatible with line
configuration
Perform
Supplemental Review
Does not qualify for
interconnection under Rule
21
Does supplemental
review determine
requirements?
Company provides the
cost estimate and
schedule for IRS to
determine requirements
Generating Facility
qualifies for
interconnection subject
to requirements, if any,
determined by
supplemental review
Generating
Facility qualifies
for Simplified
Interconnection
no
no
no
yes
yes
no
no
yes
yes
yes
yes
no
no
no
no
yes
yes
yes
yes no
Identification of areas of
risk/interest for the feeder, allows
focus of analysis on circuit-
specific issues

11. DNV GL © 2013 May 6th 2014
System Boundaries
11
Example of system
boundary
One sub-transmission
line, plus all
connected distribution
feeders

12. DNV GL © 2013 May 6th 2014
Analysis Approach
 Model load independently of solar
– Requires some manipulation of
demand data
 Find peak and minimum daytime load
days
 Run analyses with varying penetrations
of PV
 Use linear interpolation to find
technical limits
12

13. DNV GL © 2013 May 6th 2014
Analysis Approach
 Use combinations of load profile and PV penetration
13
Load Scenarios
1. Peak Daytime Load
Day
2. Minimum Daytime
Load Day
PV Penetration
Scenarios
1. No PV
2. Existing PV
3. Existing + Queued PV
4. PV = 15% of Peak Load
5. PV = 30% of Peak Load
6. PV = 50% of Peak Load
7. PV = 75% of Peak Load
8. PV = 100% of Peak Load
9. PV = 135% of Peak Load

14. DNV GL © 2013 May 6th 2014
Technical Criteria
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Technical Criterion Limit or Trigger
Steady-State Voltage V > 1.05 p.u. or V < 0.95 p.u.
Thermal Loading Loading > 100%
Backfeed Reversal of flow through transformer
Fault Current Available fault current exceeds breaker interrupt rating
Transient Voltage Voltage change > 3% during step change in PV output
Dynamic Voltage Overvoltage / undervoltage due to inverter trips during N-1
Dynamic Frequency Additional load shedding due to inverter trips during N-1
LTC Cycling Increase in LTC operations due to PV operation

15. DNV GL © 2013 May 6th 2014
LTC Cycling Studies
 An increase in LTC cycling due to PV is not necessarily a significant problem
– If it causes 1 extra operation per week, still very small change
 At some point it could become a problem, causing decrease in time between
maintenance, and LTC lifetime
– Number of increased operations per year can be calculated for each PV
penetration, and compared against a limit defined by utility
15
N
u
m
b
e
r
o
f
E
v
e
n
t
s
Change in Irradiance [W/m2s]

16. DNV GL © 2013 May 6th 2014
LTC Cycling Studies
 A reverse effect must also be studied:
– PV operation causes reduced current through LTC compared to no-LTC case
– Reduced current may increase LTC contact lifetime
– This effect reverses past point of backfeed, where increased PV causes
increased current
– Chart below comes from Kaukesha UZD LTC Technical Manual
16

17. DNV GL © 2013 May 6th 2014
Analysis in SynerGEE – Model Setup
 Load and generation on utilization circuits
aggregated to distribution transformers
 PV modeled as generator in SynerGEE (not
negative load)
– Necessary for fault analysis
– Also allows use of irradiance profiles
 Existing generators modeled in existing
locations
 Hypothetical ‘future’ generators placed by
analyst to allow up to 150% PV Penetration
17

18. DNV GL © 2013 May 6th 2014
Analysis in SynerGEE – Recipe Scripts
 SynerGEE allows use of automated
analysis
– Consecutive load flows run using
‘recipe’ commands
– Outputs saved to specified location
– Ideal for use with 24-hour load profiles
 Model Cleanup scripts can be used to
make changes between analyses
18

19. DNV GL © 2013 May 6th 2014
Analysis in SynerGEE - Solver
 SynerGEE add-on which further increases flexibility
 Allows changes to be made to model (more than Recipe or ModClean)
 Compiles and post-processes results
 Requires some basic programming skills
 Flexibility is useful in Advanced Inverter Modeling
19

20. DNV GL © 2013 May 6th 2014
Mitigation of PV Impacts
Mitigant Backfeed Loading Voltage LTC
Cycling
Fault
Current
Dynamics Transients
Energy Storage X X X X
Curtailment X X X X
Inverter power
factor control
X
Inverter
disconnection and
re-closing control
X X
Equipment
upgrades
X X X X
20

21. DNV GL © 2013 May 6th 2014
Energy Storage
21
Load > PV:
Load is fed by grid
PV > Load:
Load is fed by PV
PV > Load:
Excess PV charges
battery
Load > PV:
Load is fed
by battery
 Mitigates: Backfeed Violations, Voltage Violations
 Energy storage systems can be used to prevent backfeed from occurring
 Simple model in SynerGEE
is to calculate total reverse
power flow and energy
 New battery model in
SynerGEE 5.1 will allow
individual batteries to be
charged and discharged

22. DNV GL © 2013 May 6th 2014
Curtailments
 Curtailment is a smart inverter function
 Allows utility to either:
– Reduce output from generator to solve problem
– Disconnect generator completely
 Cost to utility is cost of ‘lost’ energy to generator
 Simple model in SynerGEE is same as for energy storage:
– Calculate total energy that would be curtailed to prevent backfeed
22

23. DNV GL © 2013 May 6th 2014
Inverter Power Factor Control
 Increasing or decreasing VAR output from inverter can regulate local voltage
23
 Single time-step can easily be
modified in SynerGEE
 Automation can run multiple
time-steps consecutively and
identify local voltage problems
using Solver:
Run load flow
Voltage
violation?
Reduce inverter
power factor
Move
to next
time-
step
No
Yes
 Complexity of process can be increased
 In practice staged reduction in power factor will
be necessary to prevent over-correction

24. DNV GL © 2013 May 6th 2014
Inverter Disconnection and Re-Closing control
 When trips and transient events happen, loss and return of all generators at once
can cause problems due to time delay on LTC
 Smart inverters provide options:
– Ramp up of output
– Variable trip settings
– Variable re-closing settings
24

25. DNV GL © 2013 May 6th 2014
Comparison of Mitigation Techniques
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26. DNV GL © 2013 May 6th 2014
Conclusion
 Pro-Active Approach can help to streamline PV interconnection process
– Can also help to plan equipment upgrades
 Analysis performed in SynerGEE allows flexibility to modify process
– Also allows automation of analysis and post-processing
 Flexibility of SynerGEE also allows approximation of advanced and smart inverter
characteristics
– Integration with energy storage
– Curtailment
– Power factor control
– Output ramping
26

27. DNV GL © 2013 May 6th 2014
SAFER, SMARTER, GREENER
www.dnvgl.com
Thank you for your attention
27
Jonathan Flinn
Jonathan.flinn@dnvgl.com
(925) 327-3044