The 4,000 inmates at Santa Rita Jail in the San Francisco Bay Area have an unusual home. The Alameda County facility boasts a microgrid, a self-contained power system consisting of a 1.2-megawatt rooftop solar array, five wind turbines generating 11.2 kilowatts, a one-megawatt fuel cell, and two megawatts worth of batteries to store all that energy.
That makes Santa Rita perhaps the world’s greenest modern jail, according to a discussion at a recent conference. It, and other large-scale infrastructure projects like it, are another sign that institutions are beginning to pull the plug on a century-old energy business model in which a monopoly utility sells electricity at a regulated rate for a regulated profit to captive customers. “We’re saving a $100,000 a year while generating our own renewable energy,” Matt Muniz, Alameda County’s energy program manager, said of the facility at a recent conference in San Francisco.
How? The jail charges the microgrid’s lithium iron phosphate battery packs—essentially a supersized version of an electric car battery—at night when electricity rates are low and the sun is not shining. During the day the 1-million-square-foot jail’s photovoltaic arrays generate electricity when rates are higher. If passing clouds interrupt the flow of solar electricity, the batteries kick in and supply power. The jail’s fuel cell—which can convert natural gas, biogas, or hydrogen into electricity through an electrochemical process—provides about half the facility’s energy.