Independent Power Producer
Independent Power Producer





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 MW and a minimum load of 85 MW, with available firm generation of approximately 268 MW. The majority 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% of the island’s peak demand.





As wind power production increases, so does the requirement for regulating reserves. Maui’s relatively small grid has a limited number of generation assets available to provide this increased reserve capacity. Additionally, the generators have minimum operating levels, resulting in reserve generators providing often-unneeded power to the grid – which, in turn, leads to curtailment of otherwise available wind power. KWP II is first in the curtailment order of the island’s three wind farms, making it the first to be curtailed and the last to be released from curtailment. As such, KWP II would have been significantly underutilized unless additional measures were taken. This unique situation led to an opportunity for Younicos to provide an energy storage solution to increase the overall acceptance of wind power from the KWP II project to the MECO grid.





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 provides up to 10 MW of “up reserve” and 8 MW of “down reserve” capability without adding any unneeded thermal generation to the grid. In addition, the system maintains the PPA-required ramp rate of ± 2 MW/minute for required hours. 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 is able to avoid running generators for the sole purpose of grid stability. One generator with a minimum operating output of 4.5 MW would be required in order 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% 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% capacity factor to the 21 MW wind farm.




turnkey energy storage system by Younicos.



for regulating reserves to be taken offline, preventing the KWP II wind farm from being curtailed



of otherwise curtailed wind generation can be now delivered to the grid.




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.