High-Renewable Grids in the Sacramento Municipal Utility District

As solar photovoltaic (PV) integration continues to grow in California, NREL has collaborated with Sacramento Municipal Utility District (SMUD) to explore solutions to accelerate advanced inverter adoption.

Community with rooftop solar homes in California.

Increasing PV integration with advanced inverters requires fast yet advanced solutions. These solutions should be affordable and streamlined to reduce work for utilities and solar planners. NREL and Sacramento Municipal Utility District (SMUD) collaborated to develop these solutions.

PREconfiguring and Controlling Inverter SEtpoints

Preconfiguration and autonomous operation of advanced inverters is the path to enabling the expansion of distributed energy systems. PREconfiguring and Controlling Inverter SEtpoints (PRECISE) is a tool that evolved from NREL's work with SMUD at the Energy Systems Integration Facility and was inspired by the surge in customer interest to connect home-installed solar to California's grid. With support from SMUD, the PRECISE team developed a real-time operation platform that enables distribution utilities to identify optimal inverter modes and settings to maximize the cost-effective use of installed PV systems.

Effects of High Renewables on Driving Point Impedance and Voltage Regulator Performance

Voltage regulators are the classic voltage support devices on distribution systems. Before distributed energy resources were introduced, power flow in a distribution feeder was unidirectional, causing a predictable loading pattern and making operation of voltage regulators easier and understandable. However, with increased renewable generation on distribution feeders, a paradigm shift is occurring in the operational expectations of voltage regulators and load tap changers.

In this collaboration, NREL reassessed the research needs to foster existing load tap changers and line-regulator controls on renewable-rich distribution systems. This study makes use of metrics such as driving point impedance, the effectiveness of tap change (tap-delta), reactive power flow, and transformer efficiency to evaluate the performance of load tap changers/line regulators on distribution feeders with substantial distributed energy resource penetrations.


Studies on the Effects of High Renewable Penetrations on Driving Point Impedance and Voltage Regulator Performance: National Renewable Energy Laboratory/Sacramento Municipal Utility District Load Tap Changer Driving Point Impedance Project, NREL Technical Report (2018)


Adarsh Nagarajan

Group Manager, Power System Design and Planning