Pushing the envelope: Utility KIUC on integrating high penetrations of solar on an isolated grid


In early November pv magazine reported on the completion of the Anahola PV plant, a 12 MW-AC solar PV and battery storage project which on its own will meet 20% of Kauai's daytime electricity demand.

With a series of other utility-scale and thousands of distributed PV projects, Kaua'i is currently meeting around 17.5% of annual electric demand with solar PV – more than twice the portion of the leading nation, Italy, and nearly three times as much as Germany. During the day, this has peaked at as high as 72% of instantaneous demand.

However, this is just the beginning. SolarCity is building another 12 MW-AC solar and storage project in Kaua'i, and by 2018 the island expects to be meeting a full 25% of annual demand with PV and battery storage.

The technical challenge of integrating this much solar is further compounded by the island's small area, its isolated grid and the lack of wind power to balance out daily production cycles. pv magazine spoke with Jim Kelly, spokesperson for island utility cooperative KIUC, about how Kaua'i is tackling this challenge.

pv magazine: The island of Kaua'i is now meeting a much higher portion of demand with solar than leading solar energy nations like Germany, Italy and Greece. Can you give a brief overview of the steps that were needed to make this technically possible?

Jim Kelly: We had to do things like modify our air permits to allow our generators to operate well below their 50% load level, tune our generator governors so that they would better complement the variability of solar, work with solar inverter manufacturers to ensure that the installations were ride-through, wide frequency and voltage excursions that are pretty common on small island systems, work with the battery inverter manufacturers to makes sure that their installations were doing the same thing.

Redesign our relay protection scheme to counter declining inertia in the system when that happens, redesign our load shed scheme to account for the wider operating scenarios we are seeing.

And just some things that are inherent to our island specifically, is that we have small, fast-start generators that are not prone to cycling damage, and we have, really, a small group of engineers who have a lot of grid operations experience who really are being driven to push the envelope, because outside of solar, there are really few alternatives to us for the high price of oil generation.

So we had to make this work.

pv magazine: What are the additional challenges posed by Kauai's relatively small geographic area and isolated grid?

Jim Kelly: The main challenge is that isolation. We are very vulnerable to huge swings in oil prices, but you know we are also vulnerable to any kind of disruption in that supply chain. So the idea of being much more energy independent is a huge part of why we are doing this.

pv magazine: In terms of wind and solar, how does being on a small island affect deployment?

Jim Kelly: First off, wind is off the table for us, because we have an endangered seabird population, that just rules out conventional wind farms. So we don't have any wind here and that isn't a viable option for us. So we are looking mostly at solar.

The main thing is, you get a frequency drop, and there is nobody you can count on to help you out. We are it. So if there is an issue that has come along during the day with one of the solar arrays, then that is something that we need to deal with ourselves. You need to ramp up conventional generation.

The frequency swings that you are seeing with solar, because of the intermittent character of it, is just, I think when we've shown it to other utilities, their minds are blown. The system is in constantly in motion all day long, between solar and conventional generation and batteries backing it up.

Kauai has a lot of cloud cover that moves in and out – it's actually a fairly rainy island. So it's very possible that on one side of the island you may be having a heavy rainstorm, so your utility-scale solar and all of your rooftop solar is going to be basically producing nothing while you are getting pretty good production from all the solar on a different part of the island.

So you are going to spend all day chasing that. And there's nobody else to rely on and jump in when suddenly when half of your frequency is dropping because of weather, cloud conditions, whatever.

pv magazine: Can you talk about the role that batteries are playing in integrating this much solar on the grid? Why is the power smoothing function necessary, and will it be necessary to use batteries to meet demand after sundown when more solar projects are built?

Jim Kelly: The batteries we are using are for smoothing, because we've got to keep that frequency stable. And that high penetration of solar that we are talking about just wreaks havoc on frequency. Again, you can have a day, every day pretty much, around here you get clouds moving in on different parts of the island, moving in, moving out quickly, so you are getting wide frequency variations, and the batteries have to be able to respond immediately, instantly and cover that, for as long as required.

So without the batteries we could not be doing the utility-scale solar that we are doing. We could not have the kind of penetration that we have.

Talking about using batteries for actually moving some of the daytime production into the night – We have a project that is right now in the permitting stage, and we hope to begin it in March, next year, of construction with SolarCity. SolarCity is going to be building a 13 MW solar array that is hooked up to a battery system that is going to be almost exclusively dedicated to peak shaving. We are going to turn that battery on at 5 o'clock at night and run it until 10 o'clock.

And we believe that is going to be – we call it dispatchable solar. We believe that this is going to be the first dispatchable solar battery system in the country. And that is not going to be used really for frequency stability but will be used exclusively to shave the evening peak, and enable us to ramp down our use of oil-fired generation even further.

pv magazine: Solar is often cited as a means to meet peak demand in other parts of the U.S. and the world, however demand curves vary by geography. What role, if any, has solar played in meeting peak demand on Kaua'i?

Jim Kelly: No. Our peak starts around 6 o'clock, and that's obviously when solar is starting to taper off, which is why we are really interested in the SolarCity project, and hoping that is an effective and cost-effective way to essentially move all of this solar that we've got during the day that is available, and move it into the night-time hours.

Kaua'i is unique in that we don't have a lot of air conditioning, we don't have any heating. We don't have any heavy industry here, we have hotels. But, during the day the tourists are out going to the beach, so the demand for air conditioning and lighting and all that kind of thing, kind of really kicks in at 6 o'clock. Everybody comes back to their hotel room, wants to take a shower, turns on the AC, that's when our peak is.

pv magazine: What should we expect for the future of renewable energy on Kaua'i?

Jim Kelly: We're really now focusing on this storage challenge. We have plenty of solar during the day, and it's cost-effective, and we feel like we've got a pretty good handle on the technical challenges of it, but now we are trying to figure out how can we put this solar to work at night, so that we again not having to be importing millions of gallons of oil.

The SolarCity project is something that we are really excited about, and that has a lot of potential. We are also looking at a pumped hydro storage project, on a part of the island where there is a pretty big elevation drop. And we can use the solar during the day to pump water uphill and at night have it run down, run like a traditional hydro.

We think that would be a terrific project for us, because it is a 100 year project, it is a proven technology, and it really puts to work all of the solar that we've got online during the day that we want to find a home for.

The issue is that we do have now is that we have plenty of solar on, in fact I think we've got more than we need during the day, and we've got over 3,000 people who put on rooftop solar. There are probably 50 people per month who are putting on rooftop solar.

So we really don't to waste it, and we don't want to curtail it, so our emphasis really now is on storage, and shifting that daytime solar into the night.

Interview conducted by pv magazine Americas Editor Christian Roselund on November 4, 2015.

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  1. In the article Jim often refers to “wide frequency variations” surely he didn’t mean ‘frequency’ as in 60hz, but more likely to variations in available generated power as the sun rises and sets, either due to time of day or to cloud cover?

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