The largest rooftop photovoltaic system in the United States will be expanded in Alameda County, on top of the county’s Santa Rita Jail in Dublin, California.OAKLAND, California, US, 2001-12-24 [SolarAccess.com] PowerLight Corp of Berkeley has been commissioned to increase the solar array from its current 640 kW to 1.14 MW by next spring. The expanded system will cover three acres of the jail’s roof, and will be the fourth-largest solar PV system in the world. The decision to expand the system “was easy because the economics were so compelling,” explains the Supervisors Board President, Scott Haggerty. “Harnessing the sun’s power to generate clean on-site electricity is not only a good investment, but it’s also a safe way to become more electrically independent and environmentally friendly at the same time.” “With solar electric generation, we are able to reduce our overall energy cost and, in particular, reduce our purchases of expensive peak energy from our local utility,” adds Matt Muniz of Alameda County. “With energy efficiency and demand side management technologies, we are able to reduce costs even further than solar alone, while at the same time revitalizing our facility.” Alameda County commissioned PowerLight earlier this year to reduce the Santa Rita Jail’s electric utility bill by displacing utility power with on-site solar power and by reducing the facility’s overall need for electricity through a combination of added insulation from solar roof tiles and a comprehensive upgrade to the jail’s central plant. To date, the combination of strategies has reduced the facility’s peak summer consumption of grid power by 25 percent, or 2 million kWh/a. Based on current power rates, the total project savings (including the 500 kW expansion) will save Alameda County $400,000 in the first year of operation and $15 million in net savings over the 25-year life of the project. The 1.14 MW system will generate electricity to supply 30 percent of the jail’s daytime needs, displacing 3 million pounds per year of CO2, NOx and SOx emissions. Alameda County did not authorize any general fund revenues to finance its solar and energy efficiency projects. Funds come from the California Energy Commission’s Emerging Renewable Buydown program, incentives from California PUC, and prior energy efficiency incentive payments. The County has also accessed a low-interest energy efficiency loan from the CEC that will be serviced by the project’s electrical cost savings.