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PNM considers new storage technologies

New, innovative technologies like hydro-pumped power storage and emerging battery systems could help Public Service Company of New Mexico power the grid in coming years as it works to transition to 100% carbon-free generation by 2040.

Those and other novel technologies are being considered as part of the company’s triennial efforts to develop a new Integrated Resource Plan that looks out 20 years into the future.

The utility files an IRP with the state Public Regulation Commission every three years to determine the most cost-effective, reliable and environmentally friendly mix of energy resources for the grid over two decades, with an immediate, four-year action plan to begin moving forward. That provides a guideline for the future that’s adjusted every three years in new IRPs to reflect changes in energy markets and generation technologies.

PNM began working in July on this year’s IRP, which will be filed with the PRC next summer, holding open meetings to get public input as it develops the plan.

Battery containers and solar panels at the PNM Prosperity Energy Storage Project at Mesa del Sol in Albuquerque. (Adolphe Pierre-Louis/Albuquerque Journal)

PNM executives say this IRP process is critically important because it covers the same 20-year period in which the utility is embarking on the most comprehensive overhaul of the grid in decades to meet state mandates included in the new Energy Transition Act, which took effect in June. The ETA calls for a foundational transformation in electric generation to eliminate all carbon-emitting resources by 2045, with at least 80% of electricity coming from renewables such as solar, wind and power-storage systems.

PNM has set a more ambitious goal for itself to achieve 100% carbon-free generation by 2040 – five years earlier than mandated by the ETA.

The law calls for utilities to reach 40% renewable generation by 2025, 50% by 2030 and 80% by 2040. To do that, the IRP process is evaluating new and emerging technologies like clean power storage to offset the intermittency of solar and wind, providing back-up generation during peak demand and when the sun isn’t shining or the wind isn’t blowing.

Today, fossil fuel plants that rely on coal, natural gas and nuclear generation provide back-up power as needed around the clock. PNM will continue to receive nuclear energy from the Palo Verde Nuclear Generating Station in Arizona through at least 2045, and possibly beyond that since it’s a carbon-free source of electricity.

A diagram of a flow battery for grid energy storage. Flow batteries are one type of power storage technology PNM is considering as it develops its new Integrated Resource Plan. (Courtesy of PNM)

But the utility’s 7 natural gas plants will be steadily phased out through 2040, starting in 2028. And it will pull out of the coal-fired San Juan Generating Station near Farmington in 2022, followed by exit from its 13% stake in the coal-fired Four Corners Power Plant in 2031.

It will replace those resources with mostly renewable generation, but it must also consider storage technologies and possibly other forms of carbon-free generation, such as carbon capture technology for natural gas “peaking plants” that can rapidly turn on and off as needed to provide back-up power.

To evaluate the viability, including cost and reliability, of those emerging technologies, PNM assembled an expert advisory group to assist in the new IRP process, said Tom Fallgren, vice president of Generation. That includes Sandia National Laboratories, the National Renewable Energy Laboratory in Colorado, New Mexico State University, the Western Grid Group and the State Land Office.

“We hold public meetings to get input on the IRP throughout the process,” Fallgren said. “But there’s a lot of debate on the state of emerging technologies, so we sought input from a technical advisory group. This way, rather than PNM just saying, ‘Here’s this and that technology we should consider,’ we’ll let the experts assess the state of new, innovative resources.”

Based on feedback from the group in early fall, PNM put out a “request for information” in November from companies developing new resources. The advisory group reviewed the responses, and in a Jan. 14 public meeting in Albuquerque, PNM presented some of the technologies it’s considering in the new IRP.

That includes both utility-side generation and demand-side management where the utility works with customers to lower their energy consumption, especially in times of peak demand. For demand-side programs, new, comprehensive software and communications systems will be needed for real-time ability to remotely turn things on and off based on rapid diagnosis of peaks and valleys in electric demand on the grid.

“We’re looking at both demand response and energy efficiency programs as part of the IRP,” Fallgren said.

It could take years before such systems are fully developed and proven for the marketplace, plus additional time to integrate them into the grid, according to PNM Financial Assessment Manager Dean Brunton.

“We need adequate communications technologies in place to integrate that,” Brunton said. “It may take multiple years to get the situational awareness we need for it.”

On the generation side, PNM and the advisory group looked at a range of technologies, including small nuclear reactors, Fallgren said.

“The first commercial deployment of that technology won’t happen until at least 2026, and it’s probably not the right resource for PNM anyway,” Fallgren said. “It’s more base-load nuclear, and we already have sufficient nuclear energy from Palo Verde through at least 2045.”

PNM to eye kinetic, battery systems

PNM is, however, looking closely at three types of power storage, including a new iron “flow battery” system, pumped hydro energy storage, and a novel system that uses concrete blocks on a tower.

That last technology is based on kinetic energy, whereby the blocks are hauled to a high elevation with power from the grid, and when backup electricity is needed, the blocks are slowly lowered. The kinetic energy from that process is used to spin a wheel to generate electricity.

“Designers claim it’s ready for commercial operation, but I say it’s still ‘pre-commercial’ technology,” Brunton said. “It’s not at the finish line yet and needs more demonstration. But we’ll look at it in the IRP modeling and ask more questions.”

In contrast, iron-based flow-battery storage seems closer to commercial deployment.

Utility-scale lithium ion batteries like those used in smartphones and laptops are already used today as backup for solar and wind facilities, including a demonstration 250-kilowatt battery storage project PNM has tested with a small solar array since 2011 at the Mesa del Sol planned community in south Albuquerque.

But those systems generally only provide between two and six hours of electricity, and PNM needs longer-duration storage capacity of up to 10-12 hours as more renewables are integrated into the grid in future years, Fallgren said.

Flow batteries could be a viable alternative. Those systems store electrical charge in tanks of liquid electrolytes. The liquids are pumped through electrodes to extract electrons. The liquids are then pumped back into the tanks for more electric storage in a close-loop system.

The tanks can be scaled up to store more power as needed, and PNM is looking at one commercially available system that uses iron as the liquid-immersed electrolyte component.

“With flow batteries, you can have tanks of unlimited size with perhaps up to 10 hours of energy storage,” Fallgren said.

Pumped hydro can also offer a potentially economical alternative. In that system, water is pumped up to a high elevation and then is used to generate hydro-based electricity as it flows back down. It’s also a closed-loop system disconnected from lakes or rivers, so it doesn’t draw down water supplies in an arid state like New Mexico, Fallgren said.

“I believe that will be a significant technology for us that could be a critical part of the solution to get to 100% carbon-free generation,” Fallgren said. “We’re seeing a lot of attempts to develop it across the U.S.”

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