Solar PV Inverter Study ( Solar Thermal Magazine)
SolarCity, in partnership with the U.S. Department of Energy’s National Renewable Energy Laboratory and the Hawaiian Electric Companies, has completed testing on the ability of solar pv inverters to mitigate transient load rejection overvoltage (LRO) concerns on Hawaiian Electric’s distribution grid.
These LRO concerns have been one of the major limiting factors governing Hawaiian Electric’s current integration policies on high penetration of distributed generation. The LRO testing is part of various other activities planned in collaboration with SolarCity, NREL and Hawaiian Electric that also includes analysis on the ability of inverters to enable increased levels of distributed solar penetration on utility distribution circuits.
The inverter testing at NREL’s Energy Systems Integration Facility (ESIF) examined ways to quantify transient LRO. That testing is one of the main technical barriers to allowing more distributed energy such as solar and wind onto the grid. Results of the testing are discussed in the report, “Inverter Load Rejection Over-Voltage Testing: SolarCity CRADA Task 1a Final Report.”
The goal of this collaborative research is to examine existing barriers to achieve increasingly higher safe and reliable integration of distributed generation on utility distribution circuits, ultimately providing insights into how to overcome these interconnection barriers. The NREL testing has already proven successful in achieving this goal. As a direct result of this testing, the Hawaiian Electric Companies announced on January 20, 2015 their intention as part of a transitional distributed generation program to dramatically increase circuit penetration thresholds for distributed generation. Specifically, coupled with the implementation of new performance settings for inverters, Hawaiian Electric announced plans to increase circuit thresholds from their current levels of 120% of daytime minimum load (DML) to 250% of DML, more than doubling the hosting capacity of circuits to integrate rooftop solar.
When implemented, this new standard for solar integration on distribution circuits will represent the highest threshold in North America.
Hawaiian Electric’s announcement of its intention to raise the minimum daytime load threshold came several months after they announced that they would “clear a queue” of net energy-metered solar customers who have been waiting to interconnect their rooftop solar systems to Hawaiian Electric’s distribution grid. Hawaiian Electric justified this announcement on early results from the NREL testing. Hawaiian Electric’s intention to increase MDL limits in conjunction with new performance settings across all circuits reinforces the promising results obtained from this research.
This SolarCity, NREL and Hawaiian Electric testing collaboration continues into several other technical topics related to the interconnection and utilization of distributed generation. SolarCity, NREL and Hawaiian Electric are currently testing the ability of inverters to mitigate ground fault overvoltage concerns. Later in 2015, testing will also examine the capability of inverters to support distribution voltage regulation, mitigate utility concerns related to bi-directional power flow, and the effectiveness of multiple inverter islanding during faults. SolarCity, NREL and Hawaiian Electric engineers continue their collaboration at NREL’s ESIF facility and will publish their findings as they become available.
This research is supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy. Funding is provided from SolarCity, the Department of Energy’s SunShot Initiative, and the Hawaiian Electric Companies.