State utility regulators are once again questioning the feasibility of a Hawaiian Electric Co. (HECO) plan to shut down a vital coal plant — this time on the island of Maui.

Those doubts were evident during an April 14 meeting between HECO and the Hawaii Public Utilities Commission to discuss the steps required to retire AES’s Kahului Power Plant (KPP) in 2024

KPP’s shutdown would follow a path similar to that of AES’s coal-fired Hawaii Power Plant on Oahu, where new renewable resources are expected to be phased in as the old plant is phased out. (See Discontent Mounts over HECO Coal Plant Closure Plans.)

HECO subsidiary Maui Electric is slated to bring on six new resources in two phases by the end of 2023 to replace KPP’s output. Stage 1 includes the Paeahu and Kuihelani solar projects, while Stage 2 consists of the Pulehu, Kamaole, and Kahana solar projects along with the Waena Battery Energy Storage System.

Complicating the shutdown is KPP’s role providing a number of key and interrelated grid functions that the new renewables must take up. In addition to replacing KPP’s energy capacity, HECO must also use the new resources to replace the plant’s voltage support, relieve transmission congestion via a switchyard, and provide the Stage 2 projects with grid-forming — or black start — capability.

Because of its role in Maui’s voltage control, KPP’s four units must be shut down sequentially to maintain grid stability while HECO transitions to renewables. The utility plans to close unit K3 in early 2024 and convert it into a synchronous condenser, a three-month process. It will then turn on K3 and shut off K4, performing the same conversion. After this six-month process, the entire plant’s fossil fuel generation will be shuttered, although units K1 and K2 will remain available if needed.

The Stage 2 renewable projects would require the installation of inverters that allow those resources to jumpstart the grid in the event of a blackout.

“That’s hampered by the fact that, in the industry, there is no standard for grid-forming functionality,” HECO Senior Vice President of Planning and Technology Colton Ching said during the April 14 meeting. The necessary inverters are a newer technology, potentially delaying the Stage 2 projects.

“It’s a prerequisite for the retirement, but what happens if there’s a project that is delayed or they aren’t successfully developed?” PUC Chief of Policy and Research David Parsons asked. “It sounds like you’re confident that if we got all the Stage 2 projects, that you would have sufficient grid-forming capability. But it’s still an area that you’re studying?”

HECO Director of Transmission and Distribution Planning Marc Asano acknowledged it is an area “we need to study further.” Without the grid-forming inverters, “the system would be unstable,” making that equipment a requirement for the KPP shutdown, he said.

Parsons asked if HECO had any opportunity to accelerate project timelines, given that the conversion of K3 and K4 is the “critical path here that has to happen [and is] the last thing on all the schedules. HECO Vice President of Power Supply Robert Isler pointed to the potential to shave off four to six months, adding that “I’m a little hesitant to go all the way to six but ­— depending on what happens with the other projects — possibly.”

‘Rebalancing’ Needed

A stern critic of HECO’s plan to shut down the Oahu coal plant, PUC Chair James Griffin said he was “uncomfortable with what I saw” in the Maui plan: “Where I stand right now is concerned, to be generous.”

Griffin questioned HECO’s claim that the KPP transition plan is “robust and resilient, and will over time maintain reliability, lower customer bills, and significantly reduce carbon emissions.”

“It seems to me we’ve set up a situation very similar to what we’re facing on Oahu,” with project delays that force a scramble to accelerate other timelines before the planned shutdowns of fossil fuel plants. “This is very much setting up a situation where, higher probability than not, [HECO will] delay the retirement, which after all the years of planning is not our first contingency.”

Ching said the utility has leeway for accelerating timelines on Maui: “Quicker engineering review times, faster pre-commercial operation testing, and all the steps there — those are things that we’ve committed to working with the developers to embed within their schedules to either move [the completion dates sooner] or, if they are facing headwinds that are causing delays, to offset those delays.”

Griffin agreed that “we all share the urgency,” but disagreed with HECO that its plan is robust enough.

“Let’s be very clear about who carries the cost and the risk when these things fall apart: It’s the public out there,” he said. “We need to be very cognizant about who’s carrying these costs and risks.”

Griffin said that Kuihelani Solar, slated for service this July, was delayed two years, preventing it from “filling in the middle” of the transition from KPP.

HECO CEO Scott Seu said “community engagement” accounted for some of the delays, forcing the company to adjust the project footprint and design.

“We don’t even know at this point if we can do all this, and then we’ll find out later that there’s still other hoops to jump through. Again, it feels to me that we’re setting up another delay in retirement,” Griffin said.

Seu said HECO “will have much better information” after completing additional studies this month.

Griffin further criticized HECO for redactions in its reports to the PUC. Citing Seu’s claim that Kuihelani was delayed due to community engagement, he said, “We’ve asked for the discussion about that, and all of that is still filed away confidentially. We’re being told that this is going to benefit the community, but we can’t even share what that discussion looks like?”

“We are still trying to work with [Kuihelani developer] AES in terms of unredacting more of the details of this information, which we have submitted and filed with the commission,” Seu said. “We’re not making this up that there were community concerns… We are trying to strike a balance.”

“I would highlight that we have obligations to the public,” Griffin said. “In my opinion, there needs to be a rebalancing of this cost and risk equation.”