Technical Assistance for the Electric Load Survey and Battery Energy Storage Recommendation at the Dry Tortugas Garden Key National Park

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This report provides a summary of energy measurement findings recorded from the generator serving Fort Jefferson, Garden Key, Dry Tortugas. Data analyzed in the report will be used to investigate the implementation of a microgrid system with energy storage. The National Park Service (NPS ' Homestead, FL) goal is to deliver electricity during nighttime hours from an energy storage bank for a clean and noiseless environment. Daytime storage energy will be supplied by the excess capacity untapped from the running diesel generator. Generator power measurements recorded, include the electric demand of the Garden Key-Fort Jefferson compound plus the Motor Vehicle Fort Jefferson (MVFJ) supply boat, as it was connected at the dock. Power measured during the nighttime hours between 10:00 PM and 6:00 AM were examined for two nights (Sept. 9-10 and Sept. 10-11). Power demand for the 8-hour period averaged 46.4 kW with a peak demand of 56.7 kW. Electricity used averaged 371 kilowatt-hours (kWh) based on the two 8-hour nighttime periods.A twenty percent (20%) size increase may be adequate to account for energy reserves and roundtrip losses (charging/discharge) of the system. Then, a minimum energy storage system capable of supplying 430 kWh's of electricity is considered. Since a maximum of 16 hours would be available to replenish the storage, about 29 kW of power would be needed. Based on analyzed data, the biggest hurdle encountered is the limited excess generator capacity available for charging at a given time of day. A grid tied photovoltaic system may be considered to increase total daytime charging capacity. Simulations performed in EGUSA using typical meteorological yearly (TMY) data for Key West, FL indicate that a 60 kW PV system could provide over 50% of the storage energy needed (72,995 kWh/yr).Life expectancy of an energy storage mechanism is taken into consideration depending on battery technology chosen. For a realistic long term service of batteries, the depth of discharge (DOD) has to be taken into consideration. Since Garden Key-Ft. Jefferson would implement a single discharge cycle per day over 8 hours, life expectancy may be easier to predict. Two suggested microgrid systems, including cost of system components are presented. The case for single and multiple (clustered) inverters systems as well as Lithium-ion and lead acid energy storage is debated.

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