The construction of new data centers could lead to transmission line overloads in the Bay Area, CAISO forecasts show.
Speaking during a 2025/26 transmission planning workshop on Sept. 24, CAISO representatives said the Los Esteros-Metcalf 230-kV line in San Jose could become overloaded in both near- and long-term panning scenarios, with data center load “exacerbating this issue.”
Potential data center loads also contributed “significantly” to forecasted line and transformer bank overloads in the De Anza region, which is north of San Jose.
And in the East Bay region of the Bay Area, two of the East Shore 230/115-kV transformer banks and the Grant-East Shore 115-kV lines also show overloads under both near- and long-term scenarios, with a major contributing factor tied to forecasted data centers, CAISO said during the workshop.
Kanya Dorland, a senior analyst at the California Public Utilities Commission, asked if forecasted overloads in Palo Alto also were due to planned data centers.
“And if it is data centers, do you have confirmation that the data centers have control of the sites that they are going to be located at?” Dorland asked at the workshop.
“We have modeled these data servers from the [California Energy Commission] load forecast,” a CAISO representative on the call said. “At this point, we don’t know which overloads are caused by individual loads.”
“You don’t have any information about what is driving the overloads?” Dorland said.
“Right now, we haven’t dug into what exactly is creating the overloads, which we plan to do after this stakeholder meeting as part of mitigation development,” the representative said. “And then, from there on, we need to coordinate with Pacific Gas and Electric to see what they are finding as part of their load interconnection study and see what upgrades are necessary.”
“It would be great to have more transparency to show the amount of overload is contributed by data center loads,” Dorland said.
The representative said the ISO can’t guarantee that “we will be able to provide that kind of information.”
In Palo Alto, CAISO said there is a planned upgrade project of a 115-kV line, which will help alleviate some of the overload issues, but other issues will continue to persist. Compared with the previous transmission planning cycle, Palo Alto’s load forecast increased by 47 MW in 5 years, 70 MW in 10 years and 78 MW in 15 years.
In CAISO’s transmission planning process in 2025, the ISO implemented a new load modifier to represent data centers — the Data Server modifier.
The ISO continues to study potential transmission system overloads as part of its transmission planning process and will include recommendations in its draft transmission plan by the end of March 2026, CAISO told RTO Insider.
