NREL, Sacramento Work Together on Interconnection Process Improvements


Every day, utilities across the country receive applications from customers requesting to connect their rooftop solar systems to the grid – up to hundreds per day and thousands per week. This high volume of interconnection requests shows no signs of slowing down as the price of photovoltaic (PV) systems decrease and states and local governments set higher renewable energy goals for their communities.

This swell in solar interconnection requests has created a new challenge for utilities because each application received requires a technical evaluation to assess the potential grid impacts of the new solar installation. This technical assessment evaluates impacts to power quality and infrastructure assets and is a key element of a utility’s interconnection approval process. Right now, utilities are evaluating interconnection applications manually, which means there is an increasing demand on already burdened distribution engineers.

To manage the growing volume of requests, utilities are increasingly turning to hosting capacity analysis to provide public visibility into the capacity of their networks to accommodate solar. The resulting hosting capacity maps provide a broad snapshot for customers to know if their local grid can accommodate—or host—new solar generation. These maps, although useful for high-level planning, still 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.

Grid researchers at the National Renewable Energy Laboratory (NREL) have partnered with the Sacramento Municipal Utility District (SMUD) to solve that pain point in the interconnection process.

“Our project team set out to understand how a utility can assess solar applications in a fast, robust fashion while still being technically thorough,” says Killian McKenna, a senior researcher in NREL’s Grid Planning and Analysis Center and the principal investigator on the effort.

Their solution was PRECISE – PREconfiguring and Controlling Inverter SEt-points – a tool that performs fast and automated interconnection assessments and seamlessly integrates with SMUD’s existing business interconnection workflow.

“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,” states Sheikh Hassan, a principal distribution engineer at SMUD. “PRECISE significantly reduces this evaluation time by instantly determining optimal inverter settings for a given location.”

PRECISE went live at SMUD on Feb. 26, 2022, and has processed over 1,700 applications in its first six months of operation, an average of 13 applications each business day and as many as nearly 30 applications in one day. The tool itself can scale to process any number of applications; through automation, data integration, and fast computing techniques, PRECISE can easily handle hundreds of applications daily.

“This is a tremendous result for our team and has ensured staff gets the help they need while speeding up the interconnection process and lowering costs for our customers,” comments Sruthi Nadimpalli, an information technology (IT) project manager with SMUD. This functionality won PRECISE an R&D 100 Award in 2019, has helped customers safely and efficiently install more solar energy in SMUD’s service areas, and has worldwide potential.

Automating this workflow is complicated. To be technically rigorous, PRECISE automates the modeling of all of SMUD’s 40,000-plus distribution secondaries – or the low-voltage distribution system connected to houses and rooftop solar – and pulls in advanced metering infrastructure (AMI) data as required. The tool also uses local irradiance measurements across SMUD’s service area and creates mathematical models of each incoming PV system. This involves modeling every component of the solar panels and their orientations, as well as the inverters and smart inverter capabilities, to make the assessment.

The whole process is automated to ensure that PRECISE pulls in data as soon as a customer’s interconnection application is created and updates business teams downstream (i.e., planning, metering, line design) once its calculations are complete, creating a streamlined solar interconnection process tailored to fit SMUD’s unique local needs.

One common scenario for SMUD customers involves requests to interconnect solar power systems larger than the grid could accommodate in a specific location. PRECISE automates an assessment of what size system the grid can accommodate and how advanced inverter functions can support approval. In these scenarios, planning engineers have this information and can work with the customer to find a solution to enable the PV system to interconnect successfully.

For every residential solar PV interconnection application, PRECISE assesses the impact of the interconnection proposal and evaluates the need to use smart inverter functions.

“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 adds. 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.

To make PRECISE happen, NREL worked closely with a SMUD team that included more than 20 personnel working over multiple departments at the utility – including geographical information system (GIS) experts, advanced metering infrastructure leads, distribution engineers, database administrators, application administrators, information technology project managers and business process experts.

NREL’s project team included Kapil Duwadi, who played the role of application developer, Aadil Latif, who automated the modeling of SMUD’s entire distribution system, and Killian McKenna, who oversaw the effort.

Close collaboration between NREL engineers and a diverse SMUD team was vital to the successful integration and automation of PRECISE. The project was the first automation of the technical interconnection evaluation process of its kind, one that could serve as a template for many utilities that wish to automate the increasing challenge of evaluating new interconnection requests.

“PRECISE is a cutting-edge PV interconnection evaluation tool that enables utilities to cost-effectively host more solar,” Hassan says.

Given this achievement, NREL and SMUD are exploring future collaborations together, now that PRECISE has linked the diverse utility data sets (e.g., meter data, GIS, interconnection applications) needed for automated evaluation of new distributed energy resources. PRECISE could now 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 future for grid planning and operations is increased automation for evaluating the health, impacts, and opportunities of increasing levels of distributed energy resources,” McKenna mentions. “PRECISE is a first step of many to reach that future.”

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