The Salt River Project 'SunDish'

 

On January 26th a demonstration of the SRP "SunDish" was presented by Salt River Project. Present were engineers from Scientific Applications International Corp. (SAIC), DTE Biomass Energy, Arizona Public Service company (APS), and representatives from the American Hydrogen Association, the Arizona Solar Energy Association, and other interested parties.

The SRP 'SunDish' is one of four that have been built and is located at the Salt River Landfill on the Salt River Indian Reservation outside Scottsdale, Arizona. Two more are nearby at the APS 'Star' facility in Tempe, Arizona, and another is located in Colorado. The 'SunDish' itself is 50' high and has stretched-membrane faceted dishes which are deflected to convex form by vacuum. The dishes have a total area of 118 sq. meters. The reflective surface itself is made up of sheets of 1.0 mm low-iron glass. The Stirling engine and generator were manufactured by STM Corporation. (Photograph-Stirling/Generator Nacelle)

The 'SunDish' system produces 22kW of power by reflecting and concentrating the sun's rays onto the receiver of a Stirling engine that operates a generator producing 480 Volt, 60 Hz, power. The resulting electricity is used by the landfill facilities and the 'SunDish' support system. Power is produced by dish Genset technology at an efficiency 20% higher than other solar systems of a similar size. The system is called a hybrid because it can be heated by renewable landfill gas or by other gaseous or liquid fuels. Hydrogen is used as a heat transfer and expansion gas which drives the pistons. (Photograph-Hydrogen Supply)

The 'SunDish' is composed of dish-shaped solar concentrators which focus and intensify the reflected solar energy on a heater attached to the Stirling engine. Electronic controls and tracking motors keep the sun focused on the receiver. Before sunrise, the dish is in a stored downward or "stow" position (See Photograph) to protect the mirrors from soiling and potential hail damage. When the sun rises, tracking motors precisely move the dish to follow the sun. Heat from the sun is converted to power in the Stirling engine/generator and fed to the electrical grid. The system continues to track the sun throughout the day until sunset when the controls put the dish again in the downward facing position. During daylight operations, if the sun is obscured by clouds, the controls will instruct the dish to go into an upward stow condition until direct radiation from the sun returns. At nighttime or during cloudy weather, landfill gas is ignited at a burner providing the needed operational heat for the engine. The unit was designed for 24-hour operation.

 

This was a dramatic and exciting demonstration, and we thank Ethel DeMarr of SRP for her time and assistance to educate us about this facinating renewable-energy technology. For more information contact SRP Environmental Services at 602-236-2630.