By Carolyn Weber. The Sewerage Commission of Northern California's Oroville region has become the first wastewater treatment plant in the United States to be powered predominantly by solar energy (80 percent). A massive 520 kilowatt solar power system installed by Sun Power and Geothermal Energy of San Rafael, Calif., will supply most of the plant's electrical needs. The plant serves 15,000 families and many industries in the area, treating approximately 1.2 billion gallons of wastewater annually. The dual-tilt solar panels were installed in November and have been tilted up into their "winter" position to capture sunlight more efficiently while the sun is low in the sky. They'll be manually dropped back to the "summer" position in February when the sun begins to move higher.