Smoky Mountains Go Solar with Joint Venture to Test NIST Water Heater in Tennessee

A novel solar water heating system developed by the Commerce Department's National Institute of Standards and Technology is now hard at work in Great Smoky Mountains National Park (Tennessee/North Carolina). The device, which uses photovoltaic cells in combination with computer technology to maximize capture of the sun's energy, was installed recently at the park's Sugarlands Visitor Center near Gatlinburg, Tenn., in a joint project involving NIST's Building and Fire Research Laboratory, the U.S. National Park Service, the Tennessee Valley Authority's Technology Advancements Division and the Sevier County (Tenn.) Electric System.

Participants hope that the year-long test of the photovoltaic solar water heater will considerably reduce the visitor center's water heating energy consumption while providing valuable "on-the-job" field data to NIST researchers looking to improve the models used to predict system performance. Two ongoing tests of the solar water heater—at NIST's Gaithersburg, Md., headquarters and at the Florida Solar Energy Center in Cocoa, Fla.—led to refinements in earlier versions of the system that resulted in the model installed in Tennessee.

Photovoltaic cells are semiconductors that convert sunlight into electrical energy. The NIST technology, patented in 1994, includes an array of PV cells, a water storage tank incorporating multiple electrical resistive elements and a controller that maximizes the conversion of solar energy into heated water. In the system, a microprocessor continuously monitors solar conditions and kicks in the appropriate electrical resistive elements for maximum energy conversion from sunrise to sunset.

The PV design avoids many of the problems inherent in traditional thermal solar water heating systems. Such systems operate when sunlight is transmitted through a transparent cover, is absorbed by a metallic plate and the energy then heats a fluid flowing under, through or over the plate.

Unlike thermal devices, the PV solar water heater operates without pipes through the roof, fluids which can freeze or be toxic (if antifreeze is used) or costly pumps that may fail. There also is no need for storage batteries to provide energy during the night or poor solar conditions. Electrical current produced by the PV cells is utilized by the resistive elements in the storage tank to directly heat water within the tank. The heated water then serves as the means of storing energy for poor weather or nighttime conditions.

The current high cost of PV cells—equal to $5 per peak watt—is expected to decline to $1.50 per peak watt within the next decade. At that cost, a PV water heater could be installed for approximately $4,000, about the same installation price for a solar thermal heater.

The TVA is funding the demonstration project at the GSMNP site. A plaque at the installation informs park visitors about the technology of the solar water heater and the collaborators' desire to "advance the use of photovoltaic cells as an alternate energy source for the future."

GSMNP personnel contributed to the project by building the solar panel support structure, mounting the photovoltaic panels, and completing the required electrical and plumbing work. As the project was totally funded by TVA, no expenditures were required by the Park Service or NIST.

For technical information about the NIST solar water heater, contact A. Hunter Fanney, B222 Building Research Building, NIST, Gaithersburg, Md. 20899-0001, (301) 975-5864, e-mail: hunter.fanney [at] nist.gov (hunter[dot]fanney[at]nist[dot]gov).

An agency of the Commerce Department's Technology Administration, NIST promotes economic growth by working with industry to develop and apply technology, measurements and standards.