Hawaii’s Solar Push Strains the Grid

The prospect of cheaper, petroleum-free power has lured the Kauai Island Utility Cooperative (KIUC) to quintuple utility-scale solar capacity over the past year, building two 12-megawatt photovoltaic arrays.  These facilities are the biggest and a significant contributor to the island’s 78-megawatt peak power supply.  When the second plant comes online this summer, peak solar output on Kauai will approach 80 percent of power generation on some days, according to Brad Rockwell, the utility’s power supply manager.

That puts Kauai on the leading edge of solar power penetration, and KIUC has bruises to show for it.  Power fluctuations from a first large plant installed in 2012 have already largely burned out the big batteries installed to keep solar from destabilizing the island’s grid.

Now KIUC is taking a second try with batteries and hoping energy storage technology has progressed sufficiently to keep the same problems from recurring.  The new system, installed beside the solar farm nearing completion on Kauai’s northeast shore, is one of the first commercial installations of grid-scale lithium-ion batteries manufactured by the French battery giant SAFT.

The intermittent nature of renewable energy sources like solar power presents a range of challenges to utilities, depending on their grid’s size and design.  Kauai’s difficulty is most acute when clouds drift over a solar plant.  That can slash a plant’s power output by 70 to 80 percent in less than a minute.  If the plant is providing a substantial share of the grid’s power, that rapid power loss can cause the frequency of the grid’s alternating current to drop well below 60 hertz, damaging customer equipment or even causing a blackout.
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Lithium-ion batteries, which KIUC is pinning hopes on now, endure cycling better than lead-acid batteries.  John Cox, KIUC’s engineering manager, says SAFT’s lithium-ion batteries are rated for four to six times as many full charge-discharge cycles as Xtreme Power’s.
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After Anahola [KIUC’s next solar plant] comes online, Rockwell expects Kauai to see days when clear skies result in solar generation beyond what KIUC’s grid can carry.  Instead of throwing away the excess, McDowall says, KIUC could use the Anahola battery storage system to absorb it and then release that power after the sun goes down.

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