Over the past few months, the electric grids on Oahu and Hawaii island have been challenged with customer disruptions. Many have been caused by damage to local neighborhood power lines but some involved rolling blackouts.

While both result in a loss of power for customers, it is important to consider these separately.

The former are usually the result of damage to the transmission or distribution lines often during storms, as was experienced by thousands of customers in Hawaii Kai on Oahu on April 14 and 15. These outages have nothing to do with how the electricity is generated.

In contrast, the rolling blackouts that have occurred recently were the result of island-wide generation supply shortages.

Simply stated, there was not enough generation or stored energy available on the island to serve the demand. This occurred four times recently, once on Oahu (Jan. 8) and three times (Jan. 30, Feb. 13 and April 15) on Hawaii island.

These types of outages, referred to in the power industry as resource adequacy shortfalls, are exceedingly rare on the mainland, where grids are larger and more interconnected. Across much of North America, utility and grid planners try to ensure these types of system-wide supply deficiencies occur no more frequently than once every 10 years.

While still rare in Hawaii, they do occur more often because the island’s grids are smaller and isolated from neighbors. On Oahu, for example, planners design to expect no more than one shortfall every four years or so.

While the most recent outages on Oahu occurred during a period of cloudy weather with low solar and wind generation, the transition to renewables is not to blame. Instead, the root cause of the rolling blackouts was unexpected outages of several of the utility’s oil-fired generating plants at a time when others were offline for maintenance.

During the Jan. 8 event, Hawaiian Electric Co. lost significant generation capacity in quick succession due to flooding at the Waiau power plant and failures at the H-Power waste-to-energy plant. As summarized in the figure below, at the time of the rolling blackouts, almost 50% of the utility’s thermal generation was unavailable going into the evening peak.

Rather than blame the transition to renewables for these generation shortfalls, we need to learn from these recent events and accelerate the installation of the new solar and storage projects which can improve the reliability and flexibility of the grid. We also need to move as quickly as possible to replace or repower the utility’s aging oil generation plants to have more reliable “back-up” generation.

Similar challenges are being experienced on the other islands. For example, when rolling blackouts were required on the Big Island on Jan. 30, approximately 57% (160 megawatts of a total capacity of 280 megawatts) was out of service, due to reliability issues plaguing the Hamakua Energy Plant, ongoing low generation from the Puna Geothermal plant and other outages and maintenance needs across the island.

While Maui customers have not experienced rolling blackouts recently, their grid is also operating under very limited reserves. According to HECO, Maui has “high future risk with insufficient margins, no room for unexpected events.” With pending oil-plant retirements in 2027-2029, significant reliability concerns are likely if new resources cannot be brought online.

Given some of the media coverage it is easy to point fingers at renewable energy sources for the recent reliability issues, labeling them as “non-firm” or “intermittent” resources. While it is true that solar output is variable and can be extremely low during periods of clouds and rain, the utility plans for those weather conditions with back-up generation.

More storage, with or without the solar, would help some but losing half of the oil-fired power plants — many in quick succession — is considerably more than what the utility plans for.

How Did We Get Here?

While variable renewables operating on the grid are not the cause of the reliability challenges, delays in bringing approved and contracted projects online before the retirement of the AES coal plant have been a contributing factor on Oahu. Analysis conducted by the Hawaii Natural Energy Institute clearly showed that connection of the planned solar plus storage projects to the grid would more than replace the AES coal plant in terms of resource adequacy.

Unfortunately, even today, more than 20 months after retirement of the coal plant, only 75 megawatts of the 140 megawatts expected to be operational before the coal plant retirement is online today. Of the 24 new solar and storage projects that were supposed to be operational across Oahu, Maui and Hawaii island, 11 projects were canceled and the remaining were delayed significantly.

More solar and storage may have helped some on Jan. 8 but, even when these and additional new resources come online, there will still be times, days or even weeks, where the output from solar and wind resources will be low. Under these circumstances, the utility will still need reliable back up generation to prevent rolling blackouts or calls for conservation.

One factor, for which the evidence is clear, is that the utility’s “firm” generators are, in fact, far from providing the reliable backup needed on the islands. HECO’s oil-fired power plants are quite old, with many older than 50 years, and operating well beyond their original design life.

The Waiau power station, a main culprit to the Jan. 8 Oahu rolling blackouts, for example, is one of the oldest steam power plants in the country. Whether due to age alone or a combination of other factors, the utility’s generators are facing increasing maintenance needs and more frequent mechanical failures.

The decreasing reliability of these plants, as measured by how often they become unavailable without warning, has been a significant and increasing problem for the past several years.

The chart below shows the percentage of firm generation, weighted by capacity, which was on unexpected, forced outage each year since 2007. On Oahu this “weighted forced outage” rate has increased from below 5% in 2007 to an astounding 20% in 2023.

The forced outage rate on Oahu has more than doubled from the time plans were being made to retire the AES coal plant to today. Computer simulations conducted by HNEI between 2021 and 2023 show that the likelihood of a shortfall in generation increases significantly when the forced outage rate increases.

Larger mainland grids have hundreds or thousands of power plants, so when a few go on outage it is not a problem. But with only 18 generating units on Oahu, any unexpected outages can cause reliability challenges. When these outages occur during periods of low solar resource or high demand, the likelihood of a shortfall increases even more.

What Happens Next? 

In the coming months, Oahu, Maui and the Big island will see a significant increase in solar and storage capacity with new projects coming online. These renewable projects will enhance flexibility and the ability to meet energy demands throughout the day and even throughout the night.

Analysis conducted by HNEI shows that while 80% or more of our total electricity needs can be provided from variable renewables with minimal curtailment, the future electricity grid will still require large amounts of reliable backup capacity. Even when all the new variable resources come online there will still be times when thermal generation or some other backup source will be needed.

As the penetration of solar and storage increases, those backup systems will be needed to run less often, meaning less fuel will be needed.

Continued and indefinite operation of the aging steam oil fleet is risky. Mechanical failures and maintenance needs will likely continue to increase. Without replacement of the current generation with more reliable backup, our ability to get our energy from renewables will be limited and we will all continue to suffer from outages due to capacity shortfalls.

Grid planners need to include not only solar and short duration battery storage, but additional resources — including firm capacity, long duration energy storage, load flexibility, and demand response.

In response to these challenges, action is needed across the Hawaii power industry. HECO will need to adapt by adjusting maintenance schedules and considering new operational strategies like pre-charging battery storage to ensure availability during critical times. State and local governments will need to expedite permitting and approval processes to ensure new resources can replace old ones in a timely manner.

Customers can also help by being informed and supporting development of renewable projects and, when appropriate, participating in programs to support grid operations such a load management programs.

With prudent planning and the integration of new clean energy resources, Hawaii’s power grid can become more renewable, and more reliable, not less.

To ensure a reliable, flexible grid for the future of Hawaii, all parties must be involved and provide effective support to the further development and deployment of technologies on the grid.