Voltage Regulation with 

Customer-Sited Resources

EUCI Hawai’i Power Summit 2017

Julieta Giraldez

NREL/PR-5D00-70562

Honolulu, Hawaii

December 1st, 2017
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• Objective: simulation of feeder 

operations with advanced inverter grid 

support functions (GSF) to understand 

operational and customer curtailment 

impacts

• Approach: Add secondary circuits to 

two HECO feeders and use of annual 

quasi-static time-series analysis with 

various GSF (volt-VAR, constant power 

factor (CPF) and volt-watt) and varying 

PV penetration levels

HECO/NREL CRADA -Voltage Regulation Operating Strategies 

(VROS) Project

• Metrics

o Annual energy PV curtailment to all rooftop PV customers with 

advanced inverters

o Increase in reactive power demand at the feeder-head from GSF

o DeltaV metric for the highest-voltage week of the year
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• Final report

o https://www.nrel.gov/docs/fy17osti/68681.pdf

• Volt-Var benefits over CPF 0.95

o Volt-Var is always as effective or more than CPF 0.95 in reducing 

over-voltages

o Volt-Var results in significantly less reactive power absorption 

(good for utilities)

o Volt-Var results in less PV kWh curtailment (good for customers)

• Activating GSF in rooftop PV systems

o With reactive power priority, as opposed to active power 

priority, is recommended to avoid momentary over-voltages

o Have no adverse impact in legacy utility voltage regulation 

equipment 

o Do not fix voltage violations due to existing legacy PV systems 

with no GSF

Summary of Findings from VROS Study
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Summary of Findings from VROS Study

 Max. PV curtailment values

much lower than expected

 Volt-Watt showed minor 

increase in PV curtailment

 Annual curtailment 

< 0.5% for 95% of customers

 Annual curtailment < 5%

for remaining 5% of customers

• Volt-Var is recommended to be used in combination with Volt- Watt to protect the system from over-voltages 

o Results in more total customers able to interconnect

o Can avoid the need for traditional upgrades
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• Secondary low-voltage circuits are approximated and modeled up 

to the customer meter, but further voltage drop/rise could occur 

between the meter and the PV system generator terminals

 The field data from the advanced inverter pilot project is expected to 

calibrate and validate the findings of this VROS Project, including 

analyzing the behind-the-meter voltage rise impacts on kWh 

curtailment 

• PV penetration cases include all PV systems interconnected with the 

ability to export (as in NEM or customer-grid-supply (CGS) tariffs 

offered by the Companies’)

 BS modeling including customer-self-supply

• DER Parties concern about % customer energy reduction 

 BS and load control impact on kWh curtailment

 Update future scenarios with non-exporting tariffs (VROS models all PV 

systems exporting!)

 Pilot project to verify kWh reduction from Volt-Watt

Caveats and Additional Scope
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• NEM customers offered ability to connect without paying for secondary 

system upgrade in exchange for participating in the Advanced Inverter 

Pilot

• Objective: Field validation of inverter-based voltage regulation functions

o Investigate impacts on feeder voltages (mainly secondaries)

o Investigate curtailment impacts on PV kWh production

o Validate VROS project feeder models with field data 

o Confirm that there are no undesired interactions among inverters or between 

inverters and utility equipment

• Functions under test:

o Non-unity fixed power factor (FPF) operation

o Volt-var control (VVC)

o Volt-watt control (VWC)

o Combinations: FPF+VWC, VVC+VWC

• Plans to expand this project to a larger number of customers

Advanced Inverter Pilot Project Overview
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Existing pilot data collection points

Distribution 

transformer

~

Grid2020 AMI Inverter AC & DC Irradiance 

Substation 

SCADA

• Irradiance: 1-second intervals (selected locations)

• Inverter measurements: V, P, Q, pf, frequency, etc at inverter terminals

o SolarEdge: 1-second intervals; Enphase: 5-minute intervals

• AMI: V, P, Q at customer meter; 1-minute intervals

• Grid2020: V, P, Q on LV side of transformer; 1-minute intervals

• Feeder SCADA data (V, P, Q, PF, LTC setting)

• All four data streams operational as of August

• Live feed to NREL’s ESIF and remote control of GSF for participants
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• How will utility and customer impacts of rooftop PV 

with GSF change with different scenarios of BS 

deployment?

• How will the charging and discharging of distributed 

BS under non-exporting and smart export tariffs 

affect day and night-time voltages?

• How much will GSF be activated with distributed BS?

• Can load control be used to minimize customer kWh 

curtailment from GSF?

Additional Research Questions
www.nrel.gov

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, 

LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding provided by the U.S. 

Department of Energy Office of Energy Efficiency and the Hawaiian Electric Company. The views expressed in the 

article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and 

the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a 

nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or 

allow others to do so, for U.S. Government purposes.

Thank you!

julieta.giraldez@nrel.gov