[Note that this article is a transcript of the video embedded above.]

In January of 2024, right on the heels of a serious drought across the state, a major storm slammed into the Hawaiian islands of Oahu and Kauai. Severe winds caused damage to buildings, and heavy rain flooded roadways. At the Waiau Steam Turbine plant, the rain reached some of the generator unit controls, tripping two units and knocking 100 megawatts of power off the tiny grid (roughly 10% of demand). The overcast weather also meant solar panels weren’t producing much electricity, and the colossal battery systems at Kapolei and Waiawa were running out of juice. Other generating units were out of service due to maintenance scheduled during the cool winter months when power demands were lowest. Then, the H-POWER trash-to-energy plant tripped offline as well. By the evening of January 8th, all of Hawaiian Electric’s power reserves on Oahu were depleted, and it was clear that they weren’t going to have enough generation to meet all the needs. And if you can’t increase supply, the only other option is to force a reduction in demand.

At around 8:30 PM, the utility implemented rolling outages across the island of Oahu to bring power demands down to a manageable level. For about 2 hours, the utility blacked out different sections of the island for 30 minutes each to minimize the inconvenience. Twice since then, as of this writing, rolling outages have been forced on Hawaii Island from unexpected trips at generators and scheduled maintenance at backup facilities, making them unavailable to pick up the slack.

When we say “power grid” we’re used to imagining interconnections that cover huge areas and serve tens to hundreds of millions of people. But populated islands need a stable supply of electricity too. Those recent power disturbances highlight some really interesting challenges that come from building and operating a small power grid, so I thought it would be fun to use the 50th state as a case study to dive into those difficulties. I’m Grady, and this is Practical Engineering. Today we’re talking about the Hawaiian power grid.

Really, I should say Hawaiian power grids, because each populated island in the state has its own separate electrical system. Around 95% of customers are served by a single utility, Hawaiian Electric, which maintains grids on Oahu, Maui, Hawaii Island, Lanai, and Molokai. Kauai is the only island with its own electric cooperative. There have been a few proposals and false starts to connect the islands through undersea transmission cables and form a single grid. It is an enormous challenge to install and maintain cables of that depth and distance. When you add in the volcanic and seismic hazards of the area and the sensitive ecology of the surrounding ocean, so far, no one has figured out how to make it feasible. So, each island has its own power plants, high-voltage transmission lines, substations, and distribution system entirely disconnected from the others. And that makes for some interesting challenges.

“Reliability” is the name of the game when it comes to running an electrical grid. It’s not that complicated to build generators, transmission lines, transformers, et cetera. What’s hard is to keep them all running 99.9% of the time, day and night, rain or snow. Yeah, some parts of Hawaii occasionally get snow. This is a graph of a typical reliability curve that helps explain why it’s a challenge. At the left end of the curve, you can get big increases with a small investment. But the closer you get to 100 percent uptime, each increment gets a lot more expensive. It really boils down to the fact that, in many ways, reliability comes from redundancy. When something goes wrong, you need flexibility to keep the grid up. But, in practice, that means you have to pay for and maintain equipment and infrastructure that rarely gets used, or at least not to its full capacity.

Hopefully, it’s clear that the graph I showed is idealized. It’s much harder to put concrete numbers to the question. The random nature of problems that arise, our inability to predict the future, and the fact that everything in a bulk power system is interconnected all make it practically impossible to know how much investment is required to achieve any incremental improvement in reliability. But it’s useful anyway because the graph helps clarify the benefits of a large power grid, also known as a “wide area interconnection.”

For one, it smooths out demand. One part of a region may have storms while another has good weather. From east to west, the peak power demand comes at different times. Some areas get sun, some get shade. But overall, demands average out and become less volatile as the grid gets bigger geographically. Larger interconnections also have more redundant paths for energy to flow, reducing the impacts of major equipment problems like transmission line outages. They have more power plants, again creating redundancy and making it easier to schedule offline time to maintain those facilities. And, the power plants themselves can be bigger, taking advantage of the economies of scale to make energy less expensive and more environmentally beneficial. Finally, larger areas have more resources. Maybe it’s windy over here, so you can take advantage and build wind turbines. Maybe this area has lots of natural gas production, so you can produce power efficiently without having to pay for expensive fuel transportation. In general, a wide area interconnection allows the costs of equipment, infrastructure, resources, and operations to be shared, making it easier to keep things running reliably. Hawaii has none of that.

Roughly 75% of the electric power in the state currently comes from power plants that run on petroleum. There are no oil or natural gas reserves in Hawaii, which means the vast majority of power on the islands comes from fuel imported from foreign countries. That makes the state very susceptible to factors outside of its control, including international issues that affect the price of oil. Each island has only a handful of major power plants and transmission lines. And when storms happen, they often hit the entire place at once. It’s easy to see why retail energy costs in Hawaii are around 3 times the average price paid across the US. Every increment of reliability costs more than the one before it, and each island has no one else to share those costs with. So, they get passed down to consumers. But, it’s not just that the grids are small.

The bulk of the remaining roughly 25% of Hawaii’s electric power not produced in oil-fired power plants comes from renewable sources: wind, solar, and a single geothermal plant. This has the obvious benefit of reducing CO2 emissions, but it also reduces the state’s exposure to the complexities of the fuel supply chain and price volatility, taking advantage of resources that are actually available on the islands. But, renewable sources come with their own set of engineering challenges, particularly when they represent such a large percentage of the energy portfolio.

Of course, renewable sources are intermittent. You don’t get power when the wind doesn’t blow or the sun doesn’t shine. That sporadic nature necessitates options for storage or firm baseload to make up the difference between supply and demand. It also makes it more complicated to forecast the availability of power to plan ahead for maintenance, fuel needs, and so on. And, it requires those storage facilities or baseload plants to ramp down and up very quickly as the sun and wind come and go. But that’s not all. Solar and wind sources are also considered “low-inertia”. Thermal and hydroelectric power plants generally use enormous turbines to generate electricity. Those big machines have a lot of rotational inertia that stabilizes the AC frequency. The frequency of the alternating current on the grid is basically its heartbeat. It’s a measure of health, indicating whether supply and demand are properly balanced. If frequency starts to deviate too much, equipment on the grid will sense that something’s wrong and disconnect themselves to prevent damage. The same is true for lots of industrial equipment and even consumer devices. When conditions on the grid fluctuate - say a transmission line or generator suddenly trips offline - the rotational inertia in those big spinning turbines can absorb the changes and help the grid ride through with a stable frequency. Solar panels and most wind turbines connect to the grid through inverters. Instead of heavy spinning machines creating the alternating current, they’re basically just a bunch of little switches. That means disturbances can create a faster and more significant effect on the grid, reducing the quality of power and making it more difficult to keep things stable. I’m planning a deep dive into how inverter-based energy sources work, so stay tuned for that in a future video. But, it gets even more complicated than that.

Of all the renewable energy on the Hawaiian islands, about half currently comes from small-scale solar installations, like those on residential and commercial rooftops. They’re collectively known as “distributed energy resources.” This has the obvious benefit of bringing resources closer to the loads, reducing strain on transmission lines. It also takes advantage of space that is already developed and builds capacity on the grid without requiring the utility to invest in new facilities. But, distributed sources come with tradeoffs. Most parts of the grid are built for power to flow in one direction, so injecting electricity at the downstream end can create unexpected loads on circuits and equipment not designed to handle it. Distributed sources also affect voltage and frequency, since something as simple as a cloud passing over a neighborhood can dramatically swing the flow of power on the network. The inverters on small solar installations are generally dumb. And I’m using that as a technical term. They can’t communicate with the rest of the grid; they only respond based on what they can measure at the point of connection. The grid operator doesn’t get good data on how much power the distributed sources are putting into the grid, and they have little control over those inverters. They can’t tell them to reduce power if there’s too much on the grid already or increase power to provide support. And inverters, especially consumer-grade equipment, can behave in unexpected and unintended ways during faults and disturbances, magnifying small problems into larger ones.

Those inverters can also make the grid more vulnerable to cyberattacks since their security depends on individual owners. It’s not hard to imagine how someone nefarious could take advantage of a large number of distributed sources to sabotage parts of the grid. And finally, distributed resources affect the revenue that flows into the utility, and this can get pretty contentious. The rates a customer pays for electricity cover a lot of different costs, many of which don’t really evaporate on a kilowatt-per-kilowatt basis if you remove that demand from the grid. Fixed costs like maintenance of infrastructure still come due, even if that infrastructure is being used at a lower capacity on sunny days. With net metering, it gets even more complicated to figure out how much that power injected into the grid is really saving, not to mention how those savings should be distributed across the customer base.

And, these challenges are only becoming more immediate. Hawaii’s Clean Energy Initiative, launched in 2008, set a goal of meeting 70 percent of its energy needs through renewables and increased efficiencies by 2030. In 2014, they doubled down on the commitment, setting a goal of completely eliminating fossil fuel use by 2045. That would take them from one of the most fossil-fuel-dependent states in the US to the most energy-independent. And, they’ve taken some big steps toward that goal. Renewable generation has gone from less than 10% to about 25% of the total already, and a host of policies have been changed to create more opportunities for renewables on the grid. Solar water heaters are now required for most new homes. Rebates are available for solar installations. The only coal-fired plant in the state was controversially shut down in 2022. And, there is a big list of solar, battery storage, and biofuel turbine projects expected to come online in the near future.

For better or worse, Hawaii has become a full-scale test bed for renewables and the challenges involved as they become a larger and larger part of the grid. Many consider natural gas to be a bridge fuel to renewables, a firm resource that is generally cheaper, cleaner, and often more stable in price than other fossil fuels. But Hawaii is hoping to leapfrog the bridge. For the climate and their own energy security, they’ve gone all in on renewables, making them a leader in the world, but also forcing them to work out some of the bugs that inevitably arise when there’s no one ahead of you to work them out first. There are some really cool innovations on the horizon as Hawaii grows closer to its goal. Smart grid technologies will add sensors and communications tools to automate fault detection, recovery, and restoration, and enable power to flow more efficiently across distributed resources. Hawaiian Electric is also testing out time-of-use rates to encourage customers to shift their power use to off-peak hours, hopefully smoothing out demands and reducing the need for expensive generators that only get used for a few hours per day.

That idea really underscores the significant challenge Hawaii faces in keeping its grids operating. Improvements and capacity upgrades help everyone, but they cost everyone too, and they cost more for every additional increment of uptime. There’s no reliability menu, and kilowatt-hours don’t come a la carte. If you’re a self-sufficient minimalist or frequent nomad who isn’t bothered by the idea of intermittent power, you can’t pay a cheaper rate for less dependable service. And if you use a powered medical device or work a high-powered, always-connected job at home, you can’t pay extra for more reliability. In many ways, Hawaiians are all in it together. Drawing that line between what’s worth the investment and what’s just gilding the electric lily is tough already with such a diverse array of needs and opinions. Doing it on such a small scale, multiplied by several islands, and with such a quickly growing portfolio of renewable energy sources only magnifies the challenge. But it also creates opportunities for some really cool engineering to pave the way for a more resilient, secure, and flexible energy future, not just for Hawaii, but hopefully all the rest of us too.