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NERC finds rooftop solar growth could create reliability challenges

An expected explosion of rooftop solar installations in several states over the next five years could create reliability challenges for the bulk power system, and grid operators would be wise to make sure they can track and manage the impacts of those resources, the North American Electric Reliability Corp. said in its 2018 Long-Term Reliability Assessment.

The rapid rate of distribute energy resource, or DER, installations "will affect not just the flow of power but also the behavior of the system during disturbances," according to the assessment released Dec. 20. Grid operators need "to coordinate the planning, installation, and operation of DERs in relation to the BPS as [the] transition to a new resource mix occurs."

The assessment officially looks 10 years out, but NERC focused much of the report on the next five years, in part because projecting what could happen in that timeframe is much easier, NERC Director of Reliability Assessment John Moura said in a Dec. 20 press call.

In addition to flagging potential reliability challenges associated with rooftop solar growth, NERC also found that reserve margin shortfalls could occur within the next five years in the Electric Reliability Council Of Texas Inc. and Midcontinent ISO and in Ontario. But for the most part, the planned generation already going through the interconnection process should help fill in the reserve margin gaps when those projects come online, the report said.

NERC also said that while the California Independent System Operator Corp. and northern Mexico should not have any issues maintaining reserve margins during peak energy usage hours, during other hours they could have as much as 152.2 MWh of energy needs unserved in 2022 and 2.3 hours of loss of load.

"NERC isn't significantly concerned, but it's a faint signal that tells us about potential risks that should be looked at that may not be occurring during the peak hour," Moura said.

As it has in some prior long-term assessments, NERC again raised concerns about some regions' growing dependence on natural gas-fired generation amid coal-fired plant and nuclear unit retirements and new utility-scale wind and solar generation coming online. But NERC determined that expected generation retirements are not likely to result in frequency response shortages at least through 2022 in both the Eastern and Western Interconnections. However, NERC recently issued a report that found under an extreme accelerated generation retirement scenario, grid operators may have to take additional steps to preserve reliability.

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Turning to rooftop solar and other distributed resources, NERC cited projections by GTM Research that about 30 GW of nonutility distributed energy resource installations are expected come online by the end of 2023, which would bring the national total to about 51 GW. California is expected to have added the most new rooftop solar capacity by 2023: 18 GW, or about 40% of its projected peak demand for that year. New Jersey, Massachusetts and New York each are projected to see between 3.5 GW and 4 GW of distributed generation added to their systems within five years.

As more rooftop solar comes online, "the effect of these resources can present certain reliability challenges that require attention," the report said. It added that grid operators need to craft data-gathering strategies to improve visibility in areas with expected growth.

"This data collection is needed to ensure accurate and valid system planning models, load forecasting, coordinated system protection, and real-time situation awareness," the report said.

NERC issued a guideline in September 2017 for modeling distributed generation, and the report noted that some regions have already started examining the situation.

The ISO New England includes expected distributed generation growth in its planning studies, and the New York ISO published a roadmap in February 2017 for integrating distributed generation in market design elements, functional requirements and tariff language. The NYISO also implemented a solar forecasting system in 2017 to integrate with its day-ahead and real-time markets that include one data stream on zonal data for behind-the-meter rooftop solar installations.

Western Electricity Coordinating is addressing modeling development and data collection procedures to ensure distributed resources are represented in interconnection models. The PJM Interconnection tracks distributed generation installations and uses the data in its load forecasts. Additionally, PJM established a subcommittee in December 2017 to investigate and resolve related issues and procedures associated with markets, operations and planning around distributed energy resources.