Distributed Energy Resources

SMUD and NREL Partner on Software to Speed Rooftop Solar Applications

Researchers at the Sacramento Municipal Utility District (SMUD) and the National Renewable Energy Laboratory (NREL) have developed a tool to make it easier for utilities to interconnect residential solar panels to the grid.

The software – named PRECISE for PREconfiguring and Controlling Inverter SEt-points – aims to help utilities identify optimal inverter modes and settings for distributed solar.

The standalone system allows utility engineers to seamlessly interconnect photovoltaic (PV) solar generation, cutting the waiting times and costs for customers, NREL said.

Utilities can receive hundreds of requests a day to connect customers’ rooftop solar systems to their grid. Each application for interconnection requires a technical evaluation to assess the potential grid impacts of the solar installation. Currently utilities are evaluating interconnection applications manually, which puts increasing demands on distribution engineers.

To manage solar interconnection requests, utilities often use hosting capacity analysis to provide public visibility into the capacity of their networks to accommodate solar installations. The resulting maps provide a snapshot that lets customers know if their local grid can accommodate new solar generation. But the maps, although useful for high-level planning, do not answer the question of whether individual solar applications can interconnect to the grid, as every interconnection can trigger unique local distribution system constraints, NREL said.

PRECISE automates the modeling of all of SMUD's 40,000-plus low-voltage distribution lines connected to houses and rooftop solar and pulls in advanced metering infrastructure (AMI) data as required.

The software also uses local irradiance measurements across SMUD's service area and creates mathematical models of each incoming solar system, including every component of the solar panels and their orientations, as well as the inverters and smart inverter capabilities. Data is pulled in as soon as a customer's interconnection application is created and updates utility planning, metering and design teams, creating a streamlined solar interconnection process tailored to SMUD's local needs.

"PV interconnection evaluation is becoming a time-consuming process as each proposed solar power system must be individually reviewed in detail to make sure it works safely with our grid," Sheikh Hassan, a principal distribution engineer at SMUD, said in a statement. "PRECISE significantly reduces this evaluation time by instantly determining optimal inverter settings for a given location."

A common scenario for SMUD customers involves requests to interconnect solar power systems larger than the grid could accommodate in a specific location. “The task to determine optimal smart inverter settings in order to maximize our PV hosting capacity will become more complex and time intensive as the number of PV interconnection applications increase," Hassan said.

Smart inverter functions can be the deciding factor on whether an interconnection must be downsized or not, and PRECISE enables that evaluation, leveraging inverter functions as needed, to help accommodate more solar onto the grid, he said.

PRECISE went live at SMUD on in February and has processed over 1,700 applications in the first six months of operation, an average of 13 applications each business day and as many as nearly 30 applications in one day. Using automation, data integration, and fast computing techniques, PRECISE could handle hundreds of applications daily, NREL said.

NREL and SMUD said they are exploring future collaborations based on PRECISE’s ability to link the diverse utility data sets needed for automated evaluation of new distributed energy resources. PRECISE could be applied to large commercial solar sites, to assess battery energy storage, or to evaluate the impact of electric vehicles as they connect to the grid, the partners said.