A Solar and Wind Integrated Forecast Tool (SWIFT) Designed for the Management of Renewable Energy Variability on Island Grid Systems

The management of solar and wind power variability on small island grid systems is an extremely demanding task due to the small size of the systems and the lack of interconnections with other systems. The Hawaiian Electric Company (HECO) family of utilities operates five island grid systems in the Hawaiian Islands with a high and growing penetration of solar and wind generation. In order to provide a tool to assist in the management of the variability, HECO has supported the development of a Solar and Wind Integrated Forecast Tool (SWIFT) that is designed to provide guidance to the management of solar and wind power variability on island grid systems.

SWIFT is built on the multi-method ensemble approach to forecasting in which the prediction that is ultimately presented to the application is based on an optimized composite of the individual methods. The optimization is based on the likely relative performance of the individual methods for each look-ahead period as well as the time-of-day, season and weather regime. The likely performance in a specific situation is diagnosed from the historical performance of the methods. The individual methods include standard cycle Numerical Weather Prediction (NWP), rapid update NWP, statistical time series models, cloud advection algorithms based on visible and infrared satellite data, weather feature detection algorithms and short-term analog-based approaches.

SWIFT provides both deterministic and probabilistic forecasts as well as intra-forecast-interval variability and inter-interval power production ramp rates for a 0-48 hour look-ahead period. There are two forecast cycles: (1) a 15-minute update cycle for the next 6 hours in 15-minute intervals and (2) a 6-hour update cycle for the next 48 hours in 1-hour intervals. Forecasts are produced for each substation that has wind or solar energy input. Individual forecasts are produced for each utility-scale wind or solar generation facility. In addition, forecasts are also produced for the aggregated distributed behind-the-meter solar generation connected to each substation.

The forecasts are provided to the grid operators through a series of tabular and graphical displays. However, work is currently underway to integrate the solar and wind forecast data into the power flow models that are part of the Energy Management System (EMS) used by the major island grids and into the data displays provided by the EMS.

The presentation will provide (1) an overview of the solar and wind penetration levels on the HECO grid systems and the associated issues that have been encountered by HECO operators; (2) a high-level description of the design of SWIFT and its components; (3) initial results from the performance evaluation of the power production forecasts; (4) examples of forecast performance in critical situations faced by grid operators; and (5) a summary of the plans for the integration of the forecast information into the EMS systems.