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Here’s How Intermittent and Firm Renewable Sources Are Factored Into Hawaii’s Power Grid


Hawaiian Electric is looking to bring more firm renewable energy to the grid over the next decade. But as new solar and storage projects come online, the definition and role of enterprise generation remains up for debate.

On Oʻahu, Kapolei Energy Storage by Plus Power is still under construction, but it will be the largest storage facility in the state when completed, according to Polly Shaw, director of policy and communications for Plus Power.

“This large-scale Kapolei energy storage facility will provide great absorption of midday solar energy to be ready when the evening peak arrives,” she told HPR.

Battery storage is an important piece of the energy puzzle because it adds stability to variable energy sources, like wind and solar. Traditionally, these resources provided power only when the wind was blowing or the sun was shining.

Renewables generally fall into two camps: intermittent or firm. Intermittent sources such as solar and wind are weather dependent and energy limited. Firm sources can produce electricity 24 hours a day, 7 days a week, whenever needed.

The waste-powered H-POWER on Oʻahu is considered a renewable business, under state law, as would a biomass, biodiesel, or geothermal power plant. But storage technology like Kapolei Energy Storage complicates these definitions.

Savannah Harriman Mate



The Kapolei Energy Storage facility is expected to be completed by spring 2023.

“Battery plus solar is a pretty reliable resource. If you just bought a battery, well, it’s not renewable at all. But if you’re going to power it with solar, and solar plus batteries, is it a renewable business? Well, that depends on your definition,” said Matthias Fripp, associate professor of electrical engineering at the University of Hawaii at Mānoa.

He also serves on the technical advisory board for Hawaiian Electric’s integrated grid planning process. Fripp pushes any hard line in the sand between what is and isn’t a renewable business.

“I would say there’s no clear definition. Every time someone comes to you using that kind of terminology – firm, revolving – you have to dig a little deeper and ask how they define it?” Fripp said.

Hawaiian Electric argues that solar and wind power combined with battery storage does not meet its definition of firm power. This year, HECO launched the tender for 500 to 700 megawatts of next-generation farm on Oʻahu.

“Storage is typically limited to about four hours and that’s what we’re looking for in our RFP,” said Rebecca Dayhuff-Matsushima, vice president of resource procurement at Hawaiian Electric. “Long-term storage, things that would last for days or weeks, is very expensive and still in its infancy in technology development. So there’s always this need for a 24-hour enterprise generation. and 7 days a week.”

Fripp agrees that this kind of corporate power has a role to play, but thinks people should be careful not to overestimate the power needed. Even though the main advantage of solid energy is that it can be used 24 hours a day, 7 days a week, Fripp says that it would be incredibly expensive to permanently use a new renewable energy production plant.

“I don’t even want to imagine how much energy that would cost. That would be bad. But again, if you only use it 3-5% of the year, it won’t have a big effect on invoices,” Fripp said. “If you use my definition of what they need, which is something that you can activate when you need it, but it won’t work all the time, then it seems to me that we need something like 150 megawatts.”

Unlike Hawaii’s current fossil-fuel plants, Dayhuff-Matsushima says HECO does not plan to use new, 24-hour, firm renewable plants.

“What we’re looking for is flexible, firm, renewable generation that we can ramp up and down, that we can turn off when it’s not needed, but is there when it’s needed so we can make sure that we are able to provide safe, resilient and reliable energy for the island,” she told HPR.

Solar and wind will still be in the lead, says Dayhuff-Matsushima, but enterprise generation may take over.

Clearway Energy Group's Mililani I Solar Project, Oʻahu's first large-scale solar power plant and storage solar power renewable energy

Office of Governor David Ige


FILE – Clearway Energy Group’s large-scale solar and storage facility near Mililani on Oʻahu.

But some say Hawaiʻi has to wonder if that role can be filled by battery storage technology.

“Battery technology is already very functional, and it is improving and evolving rapidly. And battery technology can store energy from any source, including sources that are affected by weather conditions like wind and the sun. And they can turn what we normally call intermittent energy into steady energy,” said Colin Yost, chief operating officer of RevoluSun, a solar battery and battery installation company. locally owned and operated and specializing in rooftop solar.

Kapolei Energy Storage can capture solar energy during the day for use in the early hours of the night. Yost asks, why should he stop there?

“At this time, we don’t believe the batteries work 24/7. They’re generally considered a four-hour battery or some other amount of guaranteed storage,” Yost said. “When you connect thousands of batteries to a grid, some of that power may still be available 24/7.”

“So it’s really a question of scale and a question of technology and how you integrate those resources into the larger network. And that’s where I think more discussion is needed. A bit of imagination is needed in terms of how we’re really going to make it work,” he told HPR.

Dayhuff-Matsushima says the storage just isn’t there yet. If something went really wrong, like a natural disaster, companies’ traditional generation facilities could work better and deliver electricity sooner.

The introduction of new firm renewables addresses other concerns, such as the limits of the amount of land we have available for new solar and wind farms. But Dayhuff-Matsushima says solar power and storage still have an important role to play in Hawaii’s energy strategy.

“Being able to use these facilities, solar plus storage, or any type of intermittent plus storage facility, allows us to reduce the amount of firm generation we have to use. And that’s why even if we go out and we’re looking for a new generation of renewable business, we’re going to take more fossil fuel generation out of it,” Dayhuff-Matsushima said.

Firm versus intermittent is not just semantic. These definitions are important because they shape what the grid will fundamentally look like as Hawaii tries to meet its clean energy goals. Dayhuff-Matsushima says it can be a bit of a stretch trying to measure the needs of the future against today’s technologies.

“I think a lot of people think about this 2045 goal of 100% renewable energy that we’re just going to hit – like we’re going to have all these systems in place,” she said. “But really, it will be constant because the facilities that we are putting in place today with 20-year contracts will expire in 2045. These are either going to have to be renegotiated or they are going to have to be replaced.

“It will be an ever-evolving journey, like any electrical system. It’s just that we’re moving from what was traditionally an ever-evolving journey from fossil fuels to new forms of renewable technologies,” he said. she adds. “Right now we also have to plan what is available.”

Can solar and wind power be considered as firm energy? HPR’s Savannah Harriman-Pote takes a closer look.

Extended segment on The Conversation – September 14, 2022