The test results from NREL’s recent inverter testing at the Energy Systems Integration Facility (ESIF), which was aimed at investigating means of quantifying transient Inverter Load Rejection Over-Voltage (LRO), are now in — bringing with them some progress. They will help address one of the primary technical barriers to large-scale integration of distributed generation into the grid.
Owing to the results of the tests, the utility company HECO recently announced — via a filing with the Hawaii Public Utilities Commission — its intention to increase its penetration limits for rooftop solar. The increase was pretty substantial, it’s worth noting — from the current limit of 120% of minimum daytime load (MDL) all the way up to 250%.
If these proposed changes are instituted, they will mark the highest threshold solar penetration on distribution circuits in the US.
A bit of background here — LRO conditions sometimes occur “when a local feeder or breaker opens and the power output from a distributed energy resource exceeds the local load.” It’s this that is theoretically responsible for the current limits on high penetration of distributed generation on the utility’s feeders in HECO’s territory.
Reportedly, the test results from NREL’s recent test program helped to “mitigate some of HECO’s LRO challenges generated from advanced photovoltaic inverters.”
“ESIF enables NREL and DOE to leverage strong partnerships with manufacturers and utilities to help integrate renewable energy into a smarter, more resilient energy system,” stated Bryan Hannegan, NREL’s Associate Laboratory Director for Energy Systems Integration. “NREL and its partners use state-of-the art capabilities to develop advanced PV inverter technology and successfully integrate that with plug-in electric vehicles, hybrid power systems, hydrogen fuel cells, microgrid controls and several other advanced energy technologies.”
Here’s a bit of background on NREL’s testing program via a recent press release:
NREL’s ESIF is a 182,500-square-foot user facility that is helping transform how the nation generates, delivers and uses energy by modernizing the interplay among energy sources, infrastructure, and data. ESIF offers partners access to some of the most advanced testing, research, and development capabilities in the country and was named 2014 Lab of the Year by R&D Magazine.
The collaboration among NREL, HECO and SolarCity continues, with testing on the ability of advanced inverters to mitigate ground fault overvoltage issues. Later this year, tests at ESIF will examine the capability of advanced inverters to support distribution voltage regulation, address challenges related to bi-directional power flow, and measure the effectiveness of multiple inverter islanding during faults.
Those interested can find the report here.
Image Credit: NREL
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