Arizona Solar System Moves into Niche at Landfill

May 06, 2003

Photo of the front view of two solar trackers lined up one in front of the other and each with 20 solar photovoltaic modules mounted on racks and facing up toward the sun.
Gray Wolf is the first commercial application of the tilted tracker PV system, developed by APS Star Center in Tempe. (Credit: APS)

APS and Waste Management inaugurated a hybrid solar-diesel power system on April 16th at the Gray Wolf landfill in Dewey. Waste Management operates the landfill in a remote area located about 10 miles east of Prescott in the center of the state.

The new system has eight solar arrays, each with 20 photovoltaic (PV) modules mounted on a tracker that follows the sun across the sky during the day. The trackers use a hydraulic actuators and sophisticated electronic controls to move the position of the modules by about two degrees every eight minutes in order to keep them aligned directly with the sun. The result is the modules produce more electricity than if they were mounted fixed on the ground or if they rotated only on a horizontal axis. The solar system will provide 68,000 kilowatt-hours (kWh) per year, on average, saving the landfill about $2,000 per month on its energy bill.

APS developed the trackers at its Solar Test and Research (Star) Center in Tempe. It is the first commercial application of the tracker, and APS envisions using it for similar remotely sited landfills throughout the West. Headquartered in Phoenix and formerly known as Arizona Public Service, APS is the largest electric utility in Arizona and serves about 900,000 customers.

The power system is a solar-diesel hybrid, which means it can operate on solar energy, diesel-powered generators, or both. The solar modules have peak output (rating) of 28 kilowatts (kW), and the diesel generator is rated at 50 kW. Batteries store energy produced in the PV modules throughout the day and, in turn, provide power to the landfill facilities. The diesel generator remains in standby mode until the batteries signal they have a low charge level and call for additional power.

The system replaces three diesel generators that previously powered the facility. In addition to providing cheaper electricity because it significantly reduces the expense of hauling diesel fuel to power the remote generators, the new system is quiet and substantially reduces emissions. All of which is a benefit to the 15-member staff at Gray Wolf.

The Arizona Energy Office provided funding to the project from the DOE State Energy Program (SEP).

For more information about the system and the APS Star Center, see the APS April 28th press release.