Kauai Island Utility Cooperative energy storage study
Sandia National Laboratories performed an assessment of the benefits of energy storage for the Kauai Island Utility Cooperative. This report documents the methodology and results of this study from a generation and production-side benefits perspective only. The KIUC energy storage study focused on the economic impact of using energy storage to shave the system peak, which reduces generator run time and consequently reduces fuel and operation and maintenance (O&M) costs. It was determined that a 16-MWh energy storage system would suit KIUC's needs, taking into account the size of the 13 individual generation units in the KIUC system and a system peak of 78 MW. The analysis shows that an energy storage system substantially reduces the run time of Units D1, D2, D3, and D5 - the four smallest and oldest diesel generators at the Port Allen generating plant. The availability of stored energy also evens the diurnal variability of the remaining generation units during the off- and on-peak periods. However, the net economic benefit is insufficient to justify a load-leveling type of energy storage system at this time. While the presence of storage helps reduce the run time of the smaller and older units, the economic dispatch changes and the largest most efficient unit in the KIUC system, the 27.5-MW steam-injected combustion turbine at Kapaia, is run for extra hours to provide the recharge energy for the storage system. The economic benefits of the storage is significantly reduced because the charging energy for the storage is derived from the same fuel source as the peak generation source it displaces. This situation would be substantially different if there were a renewable energy source available to charge the storage. Especially, if there is a wind generation resource introduced in the KIUC system, there may be a potential of capturing the load-leveling benefits as well as using the storage to dampen the dynamic instability that the wind generation could introduce into the KIUC grid. General Electric is presently conducting such a study and results of this study will be available in the near future. Another study conducted by Electric Power Systems, Inc. (EPS) in May 2006 took a broader approach to determine the causes of KIUC system outages. This study concluded that energy storage with batteries will provide stability benefits and possibly eliminate the load shedding while also providing positive voltage control. Due to the lack of fuel diversity in the KIUC generation mix, SNL recommends that KIUC continue its efforts to quantify the dynamic benefits of storage. The value of the dynamic benefits, especially as an enabler of renewable generation such as wind energy, may be far greater than the production cost benefits alone. A combination of these benefits may provide KIUC sufficient positive economic and operational benefits to implement an energy storage project that will contribute to the overall enhancement of the KIUC system.