Secondary Author(s)

Metzger, Donard

Report Number




This report presents an evaluation of the resources and energy systems at Fort Jefferson, located on Garden Key in Dry Tortugas National Park, Florida. Conducted by Florida Solar Energy Center staff on June 11-12, 1997, this evaluation builds on a prior evaluation conducted in May 1989. The purpose of this evaluation was to document the energy and resource needs at the site, and to identify possibilities for reduced costs through conservation measures and renewable energy options.

Approximately 700 kWh of electrical energy is used at Fort Jefferson on a daily average, supplied exclusively by diesel-fueled generators. Average diesel fuel consumption is on the order of 2400 gallons per month. The predominant electrical loads include air conditioners (65%), refrigeration (11%) and hot water heating (8%). Peak loads are estimated to vary between 50 and 70 kW, with an estimated minimum load of about 20-25 kW during late evening and early morning hours. The estimated cost of energy is $0.33 per kWh, and includes estimates of fuel delivery and maintenance costs.

Propane is used for cooking and clothes drying only, consuming approximately seventy five 100-lb cylinders per year. Fresh water is supplied by a combination of rainwater collection systems and seawater desalination from a reverse osmosis plant. A seawater distribution system is provided for all toilet facilities.

A number of conservation measures and renewable energy options are presented in this report. These include considerations for space conditioning and refrigeration equipment and other load management devices. For the purposes of evaluating renewable energy options, solar radiation and wind energy resource data for the Dry Tortugas is provided. The use of retrofit solar water heaters is evaluated, suggesting a simple payback period of three to five years. Evaluation of Resources and Energy Systems at Fort Jefferson.

Wind energy appears to be a viable resource for the site, with the annual performance of a nominal 10-kW turbine estimated to average 47 kWh/day. Although this represents only 6 percent of the average daily energy use, the simple payback period is estimated to be about four years. The use of a photovoltaic power system was investigated for supplying part of the facility loads at Fort Jefferson, however the economics suggest that this option is marginally cost-effective, with an estimated payback period of over fifteen years at $10 per kWp installed costs. The cost-effectiveness and payback periods for each of these options depends highly on the assumptions made and accuracy of existing and projected energy costs.

Based on the data in this report, conservation measures and some renewable energy options should be strongly considered by NPS personnel responsible for Fort Jefferson. One option to consider would be the U.S. Department of Energy's FEMP program for renewable energy and conservation measures. Some of the options presented in this report may be acceptable for a shared-saving plan, whereas a contractor would install systems and equipment and be paid from savings from NPS operating funds. This arrangement has proved successful for many applications, and should be considered. Even without co-funding or other external financial support, the high energy and operating costs at Fort Jefferson suggest consideration of any viable measures to reduce costs.

Date Published




Local Subjects

Buildings - Energy Conservation; Photovoltaics


Text; Document


FSEC Energy Research Center® Collection



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