Solar-Hybrid Covers Remote Landfill Needs

When the operators of the Grey Wolf landfill outside Prescott Arizona grew frustrated spending US$8000 a month to run three large diesel generators to power the facility – along with the inherent risk of fuel spills – they didn’t immediately consider using solar power to address their needs.

Dewey, Arizona – April 28, 2003 [] Instead they explored the first obvious choice that was to connect to the local power grid by running power lines out to the nearby interstate. Unfortunately, the nearby interstate was over three miles away, and the route ran through protected land that would have required burying the line. The trenching alone would have cost over US$300,000 – not including the conduit and wire. That’s when Don Cassano and his colleagues from Waste Management knew there had to be another way. Working with Arizona Public Service (APS), which has extensive experience with a variety of solar technologies through their STAR facility, Waste Management decided to install a 28 kW tracking solar PV array, with battery and diesel backup. The eight 3500 W tilted trackers use a hydraulic actuator and electronic controls to advance the position of the Sharp modules by approximately two degrees every eight minutes to maximize exposure to the sun. The 50 kW diesel generator stands by in order to maintain battery level. The 40 kW inverter, with a 50 kW surge is from Advanced Energy Systems. The average yearly output of the system is 68,000 kWh shaving US$2000 off the monthly energy bill while supplying clean, Renewable Energy for the operations and maintenance facility of 15 full time operators. And without the constant hum of diesel generators, there’s one less offensive odor for the workers to deal with. At ten years old, the landfill is relatively new and therefore not very large. That factor, combined with the extreme dryness of the area, makes methane recovery for onsite power generation impossible for the immediate future, said Cassano. Landfills in areas with more rainfall generate more gases. With an average of 12-14 inches of rain per year in this part of Arizona, methane will not likely ever be produced at a substantial level at the Grey Wolf facility. According to Cassano, though, the Environmental Protection Agency is conducting research on bioreactor possibilities where moisture is pumped directly into a landfill’s refuse to expedite methane production. The Arizona Department of Commerce Energy Office, working in partnership with APS, attained a U.S. Department of Energy grant that resulted in partial funding for the Gray Wolf hybrid PV system. The DOE was seeking applications that would provide for a remote Renewable Energy system to reduce or avoid diesel and gasoline power generation in a real-life exercise. The hope is that this project will lead to many subsequent systems being installed in Arizona and around the United States. Jesse Broehl can be reached at
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