HONOLULU (KHON2) — Oahu is now just one month away from the closure of the coal energy plant in Kapolei. It’s the island’s cheapest but dirtiest source of power. The cost of electricity after coal is still up in the air.

Hawaiian Electric said it will inform ratepayers sometime this month how much more electric bills could spike this fall. That’s because replacement solar and battery projects aren’t yet online and pricey oil generators need to be used more meanwhile.

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The final countdown begins, as the AES plant that burns coal to make electricity will shut down for good by Sept. 1.

“At least on Oahu there are these five projects coming online in 2023, one of them is going to be probably the largest solar and battery project for Oahu at least,” explained Public Utilities Commission Chairman Leo Asuncion.

While waiting for those to come online, HECO and the PUC said the utility can still generate enough power after the end of coal.

“I haven’t seen anything that would cause me to lose my sleep over having any type of dipping below the minimum reserves,” Asuncion said.

But it’s the cost that’s likely to bite because oil has to replace much of what coal once made until more renewables are online next year.

“I think for the near term, take a look at the energy efficiency of your home and things like that,” Asuncion recommended. “We have Hawaii Energy out there, our third-party energy efficiency administrator, they’re out there trying to take a look at what more can they do. Making sure — can (consumers) withstand this period of high fuel prices, high, high energy costs and the like.”

“The AES power plant has served a valuable purpose in fulfilling Oahu’s energy needs over the past three decades,” said Sandra Larsen, the Hawaii market business leader for AES. “Our loyal, hard-working employees deserve all the credit for making it possible to provide homes and businesses with essential fuel and electricity at the lowest available cost.”

When Always Investigating first reported on the price spike coming this fall, HECO said oil-generated power was expected to cost as much as five times more for the 10% to 20% of the island’s power that once came from coal.

KHON2 asked for a price update, and a HECO spokesperson said they are “still figuring that out based on recent downward oil price direction” and that they “will be putting something out to customers in early August so they are aware.”

After Oahu’s coal plant closure, Maui is also slated to cut back its fossil-fuel generation at the oil-powered Kahului plant, and debate what to do at the Maalaea plant which also runs on oil.

“Taking away the old diesel generators, but upgrading the other two generators that they have, that can kind of continue to run as kind of like standby,” Asuncion explained of the Kahului plan.

AES broke ground last week on a large solar plant on the Valley Isle, with other large-scale projects going through permitting now for Maui.

“So we’re kind of keeping our eyes on those, and hopefully they’ll come on, we can bring down Kahului, and then look at the next piece of the puzzle: What to do in Maalaea,” Asuncion said.

Always Investigating asked: After the oil-based power price hikes, is the price per kilowatt hour for all of this new cleaner power going to come back down?

Asuncion said Kauai’s more than decade-long experience converting to mostly renewables offers a light at the end of the tunnel — with price per kilowatt hour down overall, and more steady and predictable.

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“Their rates are pretty stable, and they continue to try to push farther and farther down,” Asuncion said. “They got a couple of projects online, pump storage, hydro and the like. Those are very tough, expensive projects, but it’s all to eventually drive it as low as they can.”