Enabling High Penetrations of Solar PV for Southern California Edison (A Project of California Solar Initiative RD&D Solicitation #4) Seattle, WA 11/4/2016 Kevin Schneider, Ph.D., P.E.
Enabling High Penetrations of Solar PV for
Southern California Edison(A Project of California Solar Initiative RD&D Solicitation #4)
Seattle, WA11/4/2016
Kevin Schneider, Ph.D., P.E.
Overview
Part 1: Project Overview
Part 2: Evaluating Circuit Native PV Limit
Part 3: Mitigating PV Violations
Part 4: Concluding Comments
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Part 1: Project Overview
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CSI RD&D Program Key Principals
Improve the economics of solar
technologies by reducing
technology costs and
increasing system performance
Focus on issues that directly
benefit California, and that may
not be funded by others
Fill knowledge gaps to enable
successful, wide-scale
deployment of solar distributed
generation technologies
4
Project Goals
Better understanding current grid limits for solar
penetration (native limits).
Develop technology strategies for California feeders
to obtain 100% PV penetration.
Create a cloud-based tool to study and analyze solar
PV feeder limits.
These three goals should help reduce the time and
cost required to integrate high penetration of PV on
numerous feeders.
5
100%
Get Solar PV
penetration in
California to
Know
current
system
limits
Determine
Path forward
Study Process
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ClusterDetermine
Representative Circuits (RC)
ModelCreate RC GridLAB-D
models
Native LimitsDetermine using PV adoption study and
Monte Carlo
Mitigation TechnologiesCreate Upgrade
paths & Cost estimates
30 representative circuits
were determined using
K-Means clustering. (15
of the most
representative were used
in this study)
Circuits modeled in
GridLAB-D, with
behind the meter
loads.
Models calibrated
against SCE customer
usage data.
PV adoption
models leveraged
to determine
Native limits based
on 10 operational
constraints.
Traditional and non-
traditional
mitigation strategies
developed for
circuit upgrades to
achieve 100% PV
penetration.
Project Partners
Provide distribution model, interconnection process, validation of results, and demonstration of field interconnection
Provide GridUnity software to analyze impacts, communicate to stakeholders, and manage interconnection processProvide GridUnity software to analyze impacts, communicate to stakeholders, and manage interconnection process
Determine native Solar PV penetration levels for representative feeders and identify cost-effective mitigation strategies for higher levels of Solar PV
Southern California Edison
Project SponsorsCalifornia Public Utilities Commission, California Solar Initiative, Itron
For more information, including project reports, see:
http://www.calsolarresearch.ca.gov/
Part 2: Evaluating Circuit Native PV Limit
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SCE Defined Operational Limits (For this project)
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Table 4.1 - Circuit Operational Limits and Thresholds For determining Native Limits
Violation # Violation Violation Description
1 Thermal OverloadsLimit: Exceeding any device thermal limit, 100% rating (200% for secondary service
transformers)
2 High Instant Voltage Limit: Any instantaneous voltage over 1.10 p.u. at any point in the system.
3 5 min ANSI Violation Limit: ANSI C84.1: 0.95>V>1.05 p.u. for 5 minutes at >10% of meters in the system.
4 Moderate Reverse PowerWarning: Any reverse power that exceeds 50% of the minimum trip setting of the
substation breaker or a recloser. (Requires analysis of protection coordination)
5 High Reverse PowerLimit: Any reverse power that exceeds 75% of the minimum trip setting of the substation
breaker or a recloser.
6 Voltage Flicker
Limit: any voltage change at a PV point of common coupling that is greater than 5%
between two one-minute simulation time-steps. (Adapted from the Voltage fluctuation
design limits, May 1994)
7Voltage Drop/Rise on
Secondary
Limit: 3V drop or 5V rise across the secondary distribution system (Defined as the high
side of the service transformer to the customer meter)
8 Low Average PF Warning: Average circuit power factor <0.85 (Measured at substation)
9Circuit Plan Loading
Limit
Warning: Nameplate solar exceeds 10MVA for a 12 kV circuit, 13 MVA for a 16 kV
circuit, or 32 MVA for a 33 kV circuit.
10High Short Circuit
Contribution
Warning: Total short circuit contribution from downstream generation not to exceed
87.5% of substation circuit breaker rating
Determining the Native PV Limit
For effective analysis of solar issues a simple
power simulation is not adequate.
Time-series simulations: one-minute time-series
simulations were conducted for one-week periods,
one for each of four seasons.
PV adoption model: For each scenario, PV
deployment was determined by past energy usage
and a socio-economic model. Uniform
distributions are not appropriate for distributed PV
scenarios.
At each penetration level between 5% and 100%,
in 5% increments, 50 scenarios are examined.
Each scenario requires 4 one-week time-series
simulations with one-minute time-steps.
The results from the 4,000 time-series
simulations need to be represented in an easily
accessible visualization.
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Building Type (BT) Install Size (kW) Probability of Installation (2015)
BT0 – General Miscellaneous ?? ??BT1 – Agricultural 194 0.02859BT2 – Assembly 91 0.02823BT3 – Education: Primary 149 0.09471BT4 – Education: Secondary 363 0.04289BT6 – Education: Community College 232 0.01215BT7 – Education: University 118 0.00357BT8 – Grocery 47 0.00107BT9 – Food Store 18 0.00250BT10 – Hospital 318 0.00572BT11 – Nursing Home 45 0.00715BT12 – Clinic 28 0.03788BT13 – Hotel 101 0.00643BT14 – Guest Rooms 8 0.00071BT15 – Motel 23 0.00179BT17 – Manufacturing – Light Industrial 141 0.03860BT18 – Industrial 255 0.00536BT19 – Miscellaneous Commercial 131 0.06969BT20 – Office: Large 111 0.03788BT21 – Office: Small 30 0.42102BT23 – Multifamily Residential 16 0.01072BT25 – Restaurant: Fast Food 68 0.00107BT26 – Restaurant: Sit Down 19 0.00465BT27 – Retail: Multistory Large 331 0.03002BT28 – Retail: Single-Story Large 205 0.04753BT29 – Retail: Small 39 0.01465BT31 – Storage: Unconditioned 267 0.00036BT32 – Transportation, Communication, Utilities
1850.04325
BT33 – Warehouse: Refrigerated 607 0.00179
Native Limit Curve (Circuit 11)
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Native Limit Curve (Circuit 19)
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Part 3: Mitigating PV Violations
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Traditional Upgrades
Shunt capacitors
Remove existing units
Adjust existing units
Install fixed units
Install var-controlled units
Voltage Regulators
Install substation units regulating
output voltage
Reconductor/upgrade
Primary conductor
Service transformers
Secondary drops
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Solar PV Inverter Upgrades
It is assumed that all “new” solar
above the native limit is equipped
with these controls, but there is no
retrofitting.
The controls are based on the Rule 21
Volt-var plot shown to the right.
The set points for the Rule 21 control
are fixed and do not change over time.
The second of two journal papers
being written is examining the
possibility of adjusting the default
Rule 21 values so that inverters do not
have to be over-sized.
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Battery Storage Inverter Upgrades
Substation Distributed
This is assumed to be a utility-owned asset
Controls the reactive power output of the
inverter
The control goal is to maintain the power factor
at the substation within a desired range
Control Variables:
pf_reg INCLUDED_ALT;
pf_reg_high -0.98;
pf_reg_low 0.99;
pf_target 0.98;
pf_reg_activate_lockout_time 60s;
pf_max_capacitive_Q 1000 kVAr;
pf_max_inductive_Q 1000 kVAr;
This is assumed to be a customer-owned
asset
Controls the active power output of the
inverter
The control goal is to minimize the peak
load of an individual commercial/industrial
customer
Control Variables:
charge_on_threshold -55000
charge_off_threshold -50000;
discharge_off_threshold -65000;
discharge_on_threshold -40000;
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Mitigation Example (Circuit 11)
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at X% PV Limiting Violations Traditional Mitigation: Added two new substation capacitors
One 600 kvar (Fixed)
One 600 kvar (VAR controlled) Reduced the size of one existing downstream capacitor (600
kvar to 300 kvar)
Path 1 Central energy storage unit in 15%
Path 2: 11 decentralized storage units in peak shaving control
Six Large Units, 250 kW/1,000 kWh
{Charge on=-55 kW Charge off=-50 kW Discharge on=500 kW Discharge off=300kW}
Five small units, 100 kW/ 50 kWh
{Charge on=-0.5 kW Charge off=0 kW Discharge on=5 kW Discharge off=0kW}
Cir
cuit
#11 The non-traditional mitigation upgrade path to address these violations:
15%
15% Low Average PF
Target pf 0.98, +/- 1050 kvar
Mitigation Example (Circuit 19)
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at X% PV Limiting Violations Traditional Mitigation:
5% Voltage Flicker Added two substation Capacitors
15% Low Average PF One 150 kVAR (Fixed)
One 150 Kkvar (VAR controlled)
45% 5 min ANSI Violation Added one substaion regulator controlling output voltage
to 2,380V
0% Fixed power factor control with 0.95 leading
The non-traditional mitigation upgrade path to address these violations:
Cir
cuit
#19
Part 4: Concluding Comments
All 15 circuits can support 100% penetration of PV once the proper
mitigation strategies have been applied.
Nearly 50% of SCE circuits can host less than 50% PV, where approx. 40%
can host less than 25% PV
Determining how to achieve 100% penetration on legacy circuits can be
challenging, with a mitigation leading to new violations. (domino effect)
The most common violations experienced were power factor and voltage
based.
Proper sizing of secondary drops when new solar is installed is essential.
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Concluding Comments (cont.)
Controlling circuit voltage and circuit power factor simultaneously with
capacitors is not practical at high penetrations of PV.
Energy storage is a technically viable solution for power factor, but may not
be cost effective unless it is part of a larger multi-objective control strategy.
Inverter-based Volt-VAR is not able to address low lagging power factor and
high voltages at the same time. However, Volt-VAR combined with other
traditional upgrades can be highly effective.
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