Joshua Tree National Park Cottonwood Visitor Use Complex
Department of the Interior
National Park Service
Twenty-Nine Palms, California
The Cottonwood Visitor Use Complex in sun-drenched Joshua Tree National Park is one of several National Park Service (NPS) sites that have been designated Federal Energy Saver Showcases. Until 1998, the park used 32-kW diesel generators to provide electricity to the remote Cottonwood site. Individual gasoline generators powered the park's campground amphitheaters. The U.S. Department of Energy's Sandia National Laboratories recommended that the diesel and gasoline generators be replaced by two photovoltaic (PV) systems. A 21-kW PV array, a 250-kWh bank of batteries, a 30-kW inverter and battery charger, and a 30-kW propane generator for backup power replaced the diesel generators. And a separate 2.0-kW PV system now supplies electricity to the park's amphitheaters.
Sandia also recommended several additional changes to increase energy efficiency. The park switched electric heating loads to propane, installed occupancy sensors to control lighting, retrofitted all lighting with fluorescent fixtures and lamps, equipped residences with highly efficient refrigerators, increased building insulation, and added shading structures to reduce cooling requirements.
The Federal Energy Management Program assisted NPS in evaluating financing options for the Joshua Tree project and supplied $20,000 for the changes made to increase energy efficiency. Appropriated funds would have been the least expensive way to finance the project, but, at the time of project planning, such funds were not available. Savings lost while waiting for appropriated funds to become available represented a cost greater than that of alternative financing options.
Ultimately, NPS contracted with Southern California Edison (SCE), the local utility provider. SCE installed the PV system for a 10-year fixed monthly service charge of 1.6% of the installation cost. SCE also assumed responsibility for the operation and maintenance of the system. The contract provided for the option of renewal for an additional five years at the end of the 10-year term. A buy-out schedule was also devised to allow NPS to pay for the PV system without penalty should appropriations become available.
The cost of the new PV system was $265,000, with an estimated annual operating cost of only $1,100. The simple payback (which does not include the cost of future battery replacements) is 5.4 years. Battery replacement will be necessary in 10 years and will cost $25,000.
NPS has a guideline that assigns a dollar value to pollutant emissions for inclusion in life-cycle cost analyses. In this case, basic annual operating expenses for the generators used at Cottonwood were about $27,000 per year. With the cost of emissions included, total operating costs were estimated at about $49,700 per year. Annual emissions from the generators at Cottonwood were estimated at 5,770 pounds of nitrous oxides, 286 pounds of sulfur dioxide, 218 pounds of suspended particulate, and 120 tons of carbon dioxide. The new system eliminates pollutant emissions by about 85% and lowers annual operating costs by about 90%.
According to John Williams, Buildings and Utilities Foreman at the park, "All the component parts of this project are 100% replicable anywhere the sun shines." Joshua Tree staff have taken special care in documenting the process and outcomes of the project. The staff even provide interpretive tours to high school groups wishing to learn more about renewable energy.