By Jay Landers

Among U.S. states, Hawaii has some of the most ambitious mandates for shifting from fossil fuels to renewable energy sources to generate electricity. To achieve these mandates, the state aims to rely heavily on battery energy storage systems to provide backup power when intermittent sources such as solar and wind are insufficient or unavailable. On the Hawaiian island of Oahu, a large and sophisticated battery energy storage system recently came online, marking a key point in the state’s efforts to move toward a future of 100% renewable energy.

December startup

Situated on 8 acres of industrial land, the Kapolei Energy Storage project comprises 158 Tesla Megapack 2 XL lithium iron phosphate batteries, which are about the size of a shipping container. All told, the KES project provides 185 MW of total rated power capacity, or the largest possible instantaneous discharge, and 565 MWh of energy capacity, or the maximum amount of stored energy.

The system can meet 17% of Oahu’s electricity demand for three hours at peak load or six hours at half load, Brandon Keefe, the executive chair of Plus Power — the company that developed the project — told USA Today. Plus Power “develops, owns, and operates standalone battery energy storage systems that provide capacity, energy, and ancillary services, enabling the rapid integration of renewable generation resources,” according to the company’s Jan. 11 news release announcing the start of operations at its KES facility.

As a percentage of the electricity system that it serves, the KES project is larger than any other battery storage project in the world, Colton Ching, the senior vice president of planning and technology for the Hawaiian Electric Co. Inc., told USA Today. Hawaiian Electric serves 95% of Hawaii’s 1.4 million residents on the islands of Hawaii, Lanai, Maui, Molokai, and Oahu. Each of the islands has its own independent power grid. On Oahu, Hawaiian Electric serves approximately 307,000 customers.

large batteries near a coastline
The 185 MW/565 MWh Kapolei Energy Storage project began operations on the Hawaiian island of Oahu in December. (Image courtesy of Plus Power)

Following construction that lasted from April 2022 to December 2023, the KES project began operating on Dec. 19, says Naveen Abraham, the chief engineering, procurement, and construction officer for Plus Power. “Plus Power performed the preliminary design (for the KES project) and (construction company) Moss performed the detailed design and constructed it,” Abraham says. He declined to say how much the project cost to design and construct as well as what it will cost to operate. Owned by Plus Power, the KES facility will be operated under the terms of a 20-year contract by Hawaiian Electric.

The KES facility is by far the largest utility-scale energy storage project to begin operations on Oahu. Other projects upon which Hawaiian Electric relies for storage on Oahu include the Mililani 1 Solar facility, which provides 39 MW of solar power and 156 MWh of battery storage, and Waiawa Solar, a 36 MW solar photovoltaic project that has 144 MWh of battery storage. Both projects were developed by the Clearway Energy Group.

Advanced storage system

Plus Power describes KES as the “most advanced grid-scale battery energy storage system in the world,” according to its Jan. 11 news release. Among its benefits, the storage facility can respond to the needs of Oahu’s electrical grid in as little as 250 milliseconds, significantly faster than the combustion-powered peaker plants that take “several minutes” to come online, the release notes.

The KES project also helps stabilize the grid by ensuring its proper frequency. If electricity demand and supply do not match, the frequency of a grid can change, threatening its stability. Traditionally, grids have relied on the inertia of large spinning turbines and generators in conventional power plants to maintain stable frequencies. However, this method becomes less feasible as renewable energy sources that lack such equipment gain usage. To address this issue, the KES facility provides “‘virtual inertia’ to replicate the power-smoothing function of a spinning turbine,” according to the Plus Power release.

The KES facility connects to Oahu’s electric grid near three of Hawaiian Electric’s power plants. In this way, KES can “support the reboot of those power plants in the event of an islandwide emergency, otherwise known as ‘black start’ capability,” according to Plus Power’s release.

“This is a landmark milestone in the transition to clean energy,” Keefe said in the release. “It’s the first time a battery has been used by a major utility to balance the grid: providing fast frequency response, synthetic inertia, and black start. This project is a postcard from the future — batteries will soon be providing these services, at scale, on the mainland.”

Such services are a key part of why the KES facility is critical to Oahu’s energy future, Hawaiian Electric spokesperson Darren Pai says. “KES is an important part of a portfolio of resources that work together to provide reliability and energy security on Oahu’s isolated island grid,” Pai says. “Energy storage technology that responds quickly to constantly changing conditions is an essential tool for us to use to manage the grid and operate it as efficiently as possible.”

Benefits of storage

The new battery storage system is intended to help facilitate Oahu’s adoption of more renewable, but intermittent, energy supplies. Under the terms of a 2015 state law known as Act 97, Hawaii must obtain increasing percentages of its electricity from renewable energy sources, says Mark Glick, the chief energy officer for the state of Hawaii. By the end of 2030, 40% of the state’s electricity must come from renewable energy sources. This percentage increases to 70% by the end of 2040 and 100% by the end of 2045.

On average, 28.2% of Oahu’s electricity comes from renewable energy sources, according to Hawaiian Electric’s 2022-2023 Sustainability Report. Most of this renewable energy is provided by customer-sited solar and grid-scale solar projects, followed by waste-to-energy and wind projects.

Meeting the ambitious renewable energy targets in the future will depend, in part, on the use of battery energy storage systems, Pai says. “Renewable energy resources, such as wind and solar, are essential to our future,” he notes. “Those resources do not consistently provide energy 24 hours a day. Energy storage projects can store that energy for use at night or at other times when renewable sources are not available.”

The KES facility also is expected to enable Hawaiian Electric to take advantage of some solar power that it previously was unable to use. “Customer-sited solar power has become so abundant that Hawaiian Electric must regularly ‘curtail’ or turn off large volumes of existing utility-scale solar and wind to keep the electric system in balance,” according to the Plus Power release.

“Hawaiian Electric’s modeling found that in its first five years in operation, the KES battery plant will allow the utility to reduce curtailment of renewable energy by 69% and integrate 10% more new utility-scale renewables than previous models had allowed, while providing for the continued rapid growth of individually owned renewables such as rooftop solar,” Plus Power states in its release.

The cost of cutting coal

The KES facility came online more than a year after Hawaiian Electric stopped receiving electricity from what had been the largest power source on Oahu, a 30-year-old coal-fired power plant owned by the AES Corp. The 180 MW facility, which produced up to 20% of Oahu’s electricity, shut down in September 2022, in keeping with a 2020 state law prohibiting the use of coal for electricity generation in Hawaii after 2022. (For its part, Hawaiian Electric had indicated before the passage of the legislation that it did not intend to renew its contract with AES upon its expiration in September 2022.)

After the shutdown of the coal-fired generation facility, Hawaiian Electric had to rely more on generation facilities that run on imported oil. This change in fuel resulted in higher electricity prices, which were only exacerbated by the increase in oil prices that resulted from Russia’s invasion of Ukraine in February 2022.

In response, some critics have alleged that Oahu’s recent spike in energy costs indicates that Hawaii is pushing the adoption of renewable energy too quickly. “It became apparent prior to the coal plant shutdown that this island didn’t have enough renewable projects lined up to fill” the resulting gap in power production, says Glenn Wakai, a Democratic state senator from Oahu. “Politicians put the cart far in front of the horse,” Wakai says. “To fill the gap, (Hawaiian Electric) decided to just use more oil. They went from burning the least expensive fossil fuel to the most expensive one. Ratepayers saw a 20% increase in their electricity bills in 2023.”

However, Hawaiian Electric maintains that increased battery energy storage is expected to help alleviate higher electricity costs. “KES and other energy storage projects help us integrate more renewable energy,” Pai says. “Adding more renewable resources at fixed prices over long-term contracts will help mitigate impacts from the volatility of fossil fuel prices.” Five new solar-generation projects with battery energy storage systems ranging in size from 35 MWh to 240 MWh are expected to come online in Oahu in 2024, according to Hawaiian Electric’s Renewable Project Status Board.

Ultimately, the KES project “will save customers money,” Plus Power states in its release. “The Hawaiian Electric filing for KES estimated it will reduce electric bills by an average of $0.28 per month over a 20-year contract life,” according to the release.

Glick acknowledges that using imported oil as a fuel source poses a problem because of its cost as well as its deleterious environmental effects. For these reasons, the Hawaii State Energy Office is “looking at other ways to move to less-carbon-intensive fuels to replace diesel and low-sulfur fuel oil,” Glick says. The office will release a report outlining its findings during the second quarter of 2024, he says.

Precarious position

Less than a month after the start of the KES facility, Hawaiian Electric found itself in a precarious position in terms of its Oahu operations. On the evening of Jan. 8, the utility implemented 30-minute rolling blackouts in various locations on Oahu when energy generation was insufficient to meet demand. Hawaiian Electric conducted the blackouts, which affected about 120,000 customers, for slightly more than two hours, according to a Jan. 9 news release from the utility.

The blackouts resulted from a “combination of factors and cannot be attributed to one single cause,” Pai says. Heavy rains and winds caused “weather-related complications” that shut down two large generating units at Hawaiian Electric’s 500 MW oil-fired Waiau Power Plant, he says. At the same time, a waste-to-energy power generation facility operated by a third party also shut down.

“Additionally, due to heavy cloud cover, residential and utility-scale photovoltaic systems saw reduced output throughout the day,” Pai says. “As a result, energy storage systems like KES were needed during those hours, reducing the amount of stored energy they had available during the evening,” when peak demand occurs in Hawaii, he says. “Also, production from Oahu’s wind farms fell off during the evening,” Pai notes. “As a result of all those factors, we did not have enough available generation to meet the needs of our customers.”

Although the blackouts attracted criticism from some skeptics of Hawaii’s push to transition to all renewable energy, Pai rejects the claim that an increased reliance on renewable energy caused the problems on Jan. 8. “This was the result of a rare combination of events,” he says, noting that Oahu last experienced a blackout event in 2015, when the island depended more heavily on fossil fuel generation facilities for power.

For his part, Glick says that the operational hiccup can be blamed on the “age” and “lack of readiness” of the units at the Waiau Power Plant and not Hawaii’s push to adopt renewable energy sources.

Wakai disagrees with this assessment. Hawaii’s “overly ambitious policies” mandating eventual adoption of only renewable energy supplies are “just lofty goals with no plans,” he says. “All we are doing is inflicting pain on our residents through blackouts and higher electricity bills.”

Although he supports the idea of moving away from the use of fossil fuels, the transition needs to occur “at the right time,” Wakai says. “Hawaii needs to take a breather, identify what specifically time-bound steps need to happen, hold all stakeholders accountable, and ensure firm renewable projects are fully online. Only then should we abandon fossil fuels.”

This article is published by Civil Engineering Online.