This story was originally published by Canary Media.
Hawaii closed its last coal plant on September 1, 2022, eliminating 180 megawatts of fossil-fueled baseload power from the grid on O’ahu — a crucial step in the state’s first-in-the-nation commitment to stop burning fossil fuels for electricity by 2045.
But the move raised a question that is becoming increasingly pressing as clean energy gains momentum across the United States: How do you maintain a reliable grid while transitioning from familiar fossil plants to a portfolio of small and large renewables that depend on the whims of the weather is running?
Now Hawaii has an answer: It’s a gigantic battery, unlike the gigantic batteries which was previously built.
The Kapolei Energy Storage system actually began commercial operations on the industrial west side of O’ahu before Christmas, according to Plus Power, the Houston-based firm developing and owning the project. (The company just had the good sense to wait to announce it until journalists and readers had fully returned from winter break.)
Now Kapolei’s 158 Tesla Megapacks charge and discharge based on signals from Hawaiian Electric. The plant’s 185 megawatts of instantaneous discharge capacity matches what the old coal plant could inject into the grid, although the batteries respond much faster, with a 250 millisecond response time. Instead of generating power, they absorb it from the grid, ideally when it’s flush with renewable generation, and deliver that cheap, clean power back into the evening hours when it’s most needed.
“It feels amazing to be a part of what Hawai’i and Hawaiian Electric are doing to get to 100 percent renewable energy and to play this enabling role in helping them get one step closer,” said Brandon Keefe , executive chairman of Plus Power, told Canary Media.
The building process had its setbacks, as did the broader effort to replace the coal plant with a list of large-scale clean energy projects. The Kapolei Battery was initially intended to come online before the coal plant retired. COVID has disrupted deliveries for the grid battery industry across the board, and Kapolei’s remote location in the middle of the Pacific Ocean hasn’t made things any easier. By the summer of 2021, Plus Power hoped complete Kapolei by the end of 2022, but it ended up taking another year. Even then, it joined the grid ahead of several of the other large solar and battery projects planned to replace the coal plant’s output with clean power.
Batteries replace important coal plant functions
Grid batteries work in a fundamentally different way than coal plants, so Hawaiian Electric and Plus Power created a new framework to replace what needed to be replaced. The old coal generator provided three key values to O’ahu, Keefe explained: energy (the bulk volume of electricity), capacity (the instantaneous delivery of power on command) and grid services (stabilizing functions for the grid, fickle but essential to keeping the lights on to continue).
The battery directly replaces the latter two: it matches the coal plant’s maximum power output (or “nameplate capacity,” in industry parlance), and it is programmed to provide the necessary network services that keep the network operating within the right parameters. The grid runs within a certain frequency, but events can cause the frequency to drift out of bounds, say if another power plant goes offline or a sudden rush of solar production exceeds consumption. The Kapolei project provides a first line of defense, called “synthetic inertia,” that responds to and corrects grid anomalies in real time. If the situation continues to deteriorate beyond a certain threshold, the battery’s fast frequency response kicks in as a second line of defense.
With 565 megawatt-hours of storage, the battery cannot directly replace the coal plant’s energy production, but it works with the island’s bustling solar sector to fill that role. “We are enabling the grid to add more clean renewable energy to the system to replace the energy from the coal plant,” Keefe said.
Hawaiian Electric’s modeling suggests it could reduce the curtailment of renewable energy by an estimated 69 percent for the first five years thanks to Kapolei Energy Storage, which allows surplus clean electricity that would otherwise go to waste to come onto the grid.
The utility also requested “black start capability”. If a disaster, such as a cyclone or earthquake, knocks out the grid completely, Hawaiian Electric needs a power source to restart it. The Kapolei batteries are programmed to hold some energy in reserve for that purpose. Plus Power located the project near a substation connected to three other power plants, so the battery “could be AAA to start those other plants,” Keefe said.
The combination of all these capabilities in one site – capacity, network services, black start – leads Keefe to call Kapolei “the most advanced battery energy storage facility on the planet.”
Model for a reliable clean energy grid
The new battery is just the latest shipment from Hawaii’s longtime place at the forefront of the energy transition. It is the state that first hit mass rooftop solar adoption and the first utility-scale solar battery plant in Kauai. (Not coincidentally, Plus Power CCO Bob Rudd had a hand in that project during his tenure at Tesla.)
But when renewable energy growth and fossil plant retirements exceed a certain threshold, as in Hawaii, simply adding more wind, solar or batteries is not enough. The clean technologies, which work on digitally controlled inverters, must start to maintain the grid, not just to feed it.
Many other batteries provide frequency services to other networks, and a few of them are larger than Kapolei. But it’s the only large-scale battery we’ve seen capable of combining the basic peak capacity, frequency response, synthetic inertia and grid-recharge tasks. This is because Kapolei plays a more central role in its network than battery plants do elsewhere.
After years of construction, California’s grid battery fleet Surpassing 5,000 megawatts installed last year, but that equates to just 7.6 percent of the giant signboard capacity of the state’s network. Kapolei alone accounts for about 17 percent of Oahu’s peak capacity. Hawaiian Electric needed to take on more responsibility than batteries elsewhere ever had to.
Take inertia, which stabilizes grid frequency, as one example. Old plants provide this passively, through the rotating mass of their turbines; inertia did not need to be separately defined and compensated for in past decades because it was part of the package of running a power plant.
Now, across the country, the grid is moving to a model of maximizing cheap renewable energy when it’s available and burning fuel when renewable energy isn’t. But the thermal plants must run to provide inertia — sometimes, on the mainland, renewables are curtailed to keep old coal plants running so they can provide these grid services, Keefe said. This could be a bad deal for electricity customers, not to mention the climate.
Advanced batteries provide a synthetic version of this inertia through skillful programming of their converters. This provides a more economical alternative while avoiding unnecessary carbon emissions. They’re also faster and more precise – Keefe likened the Kapolei battery to a zip electric sports car compared to the clunky diesel bus of old thermal plants. This makes batteries a good technical fit for grids that are becoming increasingly erratic due to the fluctuations of renewable production.
Long-term, US climate goals require a phase-out of fossil fuels from the electric grid. Hydro and nuclear plants help provide valuable grid inertia without carbon emissions, but they are not on track to grow.
That is why this project is important for the clean energy shift everywhere: It is one of the first real examples of how to shift critical network functions from fossil fueled plants to clean energy plants. And eventually, the kind of network services that Kapolei pioneered will need to scale nationwide.
