The Maui Electric Company (MECO) owns and operates the electric grid and most of the generation assets on the island of Maui, Hawaii. The island has a peak load of 200 megawatt (MW) and a minimum load of 85 MW, with available firm generation of approximately 268 MW. Most of this generation is fueled by various forms of imported oil. Prior to 2012, the 30 MW Kaheawa Wind Power I (KWP I) project was the only operating wind farm on Maui. However, adding the KWP II (21 MW) and Auwahi (21 MW) wind farms in 2012 increased available wind power capacity to 72 MW, or 36 percent of the island’s peak demand.
First Wind selected Younicos to provide a 10 MW turnkey energy storage system to meet the power purchase agreement (PPA) requirements of MECO, and reduce curtailment. The storage system consists of ten 1.125 MVA Power Conversion Systems (PCS) integrated with 45 minutes of advanced lead-acid battery technology that are managed by Younicos controls and proprietary software. The system monitors the grid 100 times per second to determine the appropriate response. It instantaneously and automatically adjusts its control mode and responds within 50 milliseconds. Per MECO requirements, the system also provides fast and accurate inertial frequency response for any frequency deviations outside of 59.9 Hz – 60.1 Hz. The utility can also call on the storage system via Automatic Generation Control (AGC) to increase or decrease its output at any time to support grid needs. It thus provides multiple services simultaneously while also prioritizing services automatically as defined.
With the battery system providing regulating reserves, MECO avoids running generators for the sole purpose of grid stability. One generator with a minimum operating output of 4.5 MW would be required to meet the up-reserve requirement. In addition, it enables MECO to back down generators providing down reserve by 3 MW. This results in a total of 7.5 MW of capacity for regulating reserves to be taken offline, preventing the KWP II wind farm from being curtailed. Using a conservative estimate based on the 7.5 MW reserve capacity normally running 8 hours per day for 80 percent of the year, over 17.5 GWh of otherwise curtailed wind generation can be delivered to the grid. This is equivalent to adding >9.5 percent capacity factor to the 21 MW wind farm.
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