As of today, 8 percent of the Public Service Company of New Mexico’s customers—approximately 41,000 customers—have solar panels or battery storage on their properties, according to Omni Warner, the utility’s director of distribution engineering.

PNM expects that percentage will grow to roughly a quarter of customers generating some of their own electricity in 2040.

“It’s a significant amount today,” Warner said. “It’s going to be even larger by 2040. It’s going to grow.”

Warner and Mark Fenton, PNM’s executive director of regulatory policy and case management, presented information about PNM’s system to the New Mexico Public Regulation Commission on Tuesday during a workshop about existing practices for distributed planning. 

All three investor-owned utilities presented details about their existing practices.

Distributed planning includes preparing for increasing levels of solar from rooftop and community arrays and is an important part of grid modernization.

The information gathered during workshops like the one on Tuesday will help the PRC develop rules.

Art O’Donnell, the PRC’s director of policy administration, said the statistic that stood out the most to him during the workshop was that a quarter of PNM customers will have rooftop solar in 2040.

“I think it’s important for the commission to recognize the drivers behind this need for distribution planning,” he said. “And it’s not just policies that are put in place by the legislature, legislature and the governor and the Commission, but also consumer demand consumer preference.”

The increasing levels of solar will lead to the need to update the distribution system.

This is in part because traditionally, electricity flowed only one way on the lines—from generation sources to houses. Now electricity is flowing both ways as customers are generating solar power that is then placed onto the grid.

Zachary Pollock, the director of grid strategy and emerging technology at Xcel Energy, broke this down during his presentation. Southwestern Public Service Company, which serves part of New Mexico, is a subsidiary of Xcel Energy.

“New Mexico has very aggressive state policy goals,” Pollock said. “We’re expecting to see rapid dynamic load growth on our distribution system from the electrification of transportation, the electrification of heating. So keeping all those things in mind, I just want to reiterate that we really are seeing a lot more dynamic impacts on our system.”

Pollock said SPS has about 400 feeders on its system and is building more to meet demands. The utility has to understand how much energy the customers served by those feeders will need and how much those customers might produce from rooftop solar.

Rooftop solar means changes from how utilities have planned distribution in the past. 

“We historically have not been in the business of understanding and forecasting where customers are putting those resources on our system, as well as understanding the impacts of those.” Pollock said.

In some parts of the distribution system, there is so much solar power from customers that utilities are having to turn away applications from customers wanting to install solar panels on their roofs because the infrastructure is not able to handle it without upgrades.

Warner said the amount of solar on PNM’s lines is increasing. He said that about 5 percent of the utility’s distribution feeders are currently at solar saturation. What that means is that 90 percent of that feeder is connected to solar, he explained.

The number of solar saturated feeders is expected to increase when the community solar projects come online. 

Warner said PNM expects six to 10 additional feeders to reach solar saturation levels.

That makes it harder to bring new solar on in those areas without making infrastructure upgrades. 

Furthermore, Warner said that 35 percent of PNM’s feeders have high levels of solar penetration, meaning that the amount of solar generated during the daytime exceeds the demands for electricity in that area.

PNM is not the only one struggling with the amount of solar coming on line. Even El Paso Electric, which has had less interest in customer-owned solar than the other two utilities, has faced challenges, according to William Tye Pollard, a distribution systems engineer with EPE.

Another challenge utilities face is the supply chain. Right now, it takes 18 months to get new equipment. That means planning has to be done two to three years in advance despite the dynamic and changing nature of the grid, according to Fenton. 

Because of that dynamic nature, Pollock said it is important that any rule that the PRC adopts has flexibility.

PRC Commissioner James Ellison said that his intention with the rulemaking is not to interfere with day to day operations at utilities. However, he said he would like to see the distribution plans that the three utilities all said they produce on a basis of every three to five years.