GREAT SMOKY MOUNTAINS 
NATIONAL PARK
PHOTOVOLTAIC SOLAR 
WATER HEATING SYSTEM

The hot water used for hand washing in the rest rooms at the Sugarland's Visitor Center within the Great Smoky Mountains National Park is being heated by a photovoltaic solar water heating system. The system uses photovoltaic cells, pictured at right, that convert sunlight to electricity. The voltage and current at which the photovoltaic cells operate at maximum efficiency varies with solar intensity and ambient temperature. A microprocessor continuously selects various combinations of six heating elements so that the resulting voltage and current closely coincide with the values at maximum efficiency.

The system uses a two-tank configuration. The tank that contains the six selectable heating elements serves as the preheat tank. When hot water is being used it flows from the 80-gallon preheat tank into the 50-gallon auxiliary water heater, where it is heated further when necessary, such as on cloudy days. The auxiliary water heater is connected to the electric utility. The system was installed as a joint cooperative venture with the Tennessee Valley Authority, National Institute of Standards and Technology, Sevier County Electric System, and the National Park Service. The system will be monitored to determine its performance over a one year interval.

Frequently Asked Questions

• Who developed the photovoltaic solar water heating system? Two mechanical engineers, A. Hunter Fanney and Brian P. Dougherty, with the National Institute of Standards and Technology (NIST) developed and patented the system in 1994.
  
  
• Who paid for this system? The Tennessee Valley Authority (TVA) purchased the hardware, and provided funding to NIST to monitor the performance of the system for a one-year interval. TVA also covered the labor cost for the Great Smoky Mountains National Park (GSMNP) personnel to build the solar support structure, mount the photovoltaic panels, and install the required plumbing and electrical work.
  
  
• Can I buy one? At the current time the system is not available from a manufacturer. There are two other demonstration sites currently in operation - One at NIST in Gaithersburg, Md. and one at the Florida Solar Energy Center at Cocoa, Florida. NIST is currently looking for industrial partners to commercialize the technology.
  
  
• How does this system compare to solar thermal hot water systems? Solar thermal systems heat water by pumping water or an antifreeze solution through solar collector panels. These systems require the use of pipes and circulating pumps to transport the fluid from the storage tank through the solar collectors. In warm climates another type of solar thermal hot water system heats water directly by exposing a storage tank to the sun. The photovoltaic solar water heating system does not require a circulating pump or pipes to transport the collected energy to the storage tank. It uses conventional house wiring to transport the electrical energy to the storage tank.
  
  
• Would the photovoltaic water heating system be suited for a northern climate? Yes. The freeze concern associated with a solar thermal system is eliminated because there are no fluids present in the exterior portion of the system.
  
  
• How much electrical power does the system produce? Under clear sky midday conditions each photovoltaic module produces approximately 53 watts. There are 40 photovoltaic modules in this system resulting in a peak power output of approximately 2100 watts.
  
  
• Why and how is the system being monitored? The system is being monitored to learn how well the system performs and to collect solar radiation data for the GSMNP personnel. The system performance data will be used by NIST to verify computer prediction models being developed by the University of Wisconsin. TVA will use the data to document the potential for reduction in energy and peak demand on their utility. The system is being monitored by measuring the energy supplied by the photovoltaic array, the energy supplied by the electrical utility grid, and the gallons of water consumed. Data is collected every 10 seconds and forwarded weekly to NIST for analysis.
  
  
• How much would a system installed on my house cost and is it currently cost effective? At current photovoltaic cell costs, the estimated installed cost for a 30-panel system is $8900 which is not cost effective. However photovoltaic cell costs have declined dramatically and are projected to continue to decrease. In 1982 the average price of photovoltaic cells was $11.00 per peak watt. Currently the price is approximately $5.00 per peak watt. At a price of $1.50 per peak watt, the system would cost approximately $3,400 equivalent to that of some solar thermal hot water systems.
  
  
• Who can I contact to obtain additional information on the system? Send your request for information to Paula Svincek - National Institute of Standards,100 Bureau Drive, Gaithersburg, MD 20899-8632; 
  Fax (301) 975-5433; E-mail PVSOLAR@nist.gov