In northern California, a problem was brewing at the jail. Santa Rita County Jail required a lot of power to keep its inmates safe: Three megawatts of secure, reliable power 24 hours a day, seven days a week, with an annual utility bill topping $3 million. To cut costs and increase efficiency, Alameda County (where Santa Rita is located) is trying an innovative approach to its power problem: creating its own microgrid to power the jail on-site.
Alameda County officials saw that the jail, which is the nation’s fifth-largest and can hold up to 4,000 prisoners at one time, was sucking up more power than any other county building. They wanted to reduce its bill--and maintain a secure power supply to the facility. The jail has a campus-style design, laid out over a one-half mile long by one quarter-mile wide site with 18 separate housing units, and a handful of administration buildings used for booking, release, and administration as well as warehouses, laundry, commissary, and kitchen facilities.
The first step was to install the nation’s largest rooftop solar system (1.2 megawatts) at the jail. They then added a 1-megawatt fuel cell to produce both power and heat. Wind turbines followed, and now four giant batteries store power, so the jail can automatically disconnect itself from the grid if a power disruption occurs and operate independently until local utility power is restored. Special control units manage the flows of energy from each source. Currently, the jail produces 8,000,000 kilowatt-hours of electricity (about half of what the facility needs) and 18% of its heat requirements. Just this year, the jail installed solar trackers to boost efficiency and give its solar panels the ability to chase the sun across the sky.
The microproject doesn’t have to work alone: the jail’s grid is able to utilize two-way communications, so that Santa Rita Jail can operate in parallel with the local power company’s distribution grid or independent of it. The system runs microcontrollers at each generation site as well as industrial lithium-ion storage batteries capable of holding 4 megawatt-hours’ worth of power. All together, the system is saving the county about $100,000 per year.
Perhaps jails aren’t the first place to think of energy technology, but their specific requirements for safe and always-available power (think of what would happen to electronic locks when the power goes out) make them ripe for innovation. In addition to the energy updates at the Santa Rita jail, the facility also boasts a robotic
system speeds delivery of laundry, supplies, and food to all areas of the 113-acre campus.
Microgrids are becoming more popular in places that can’t afford even a momentary power blip--places like hospitals, data centers and military bases. But as the price of giant batteries and renewable energy sources goes down, the grids will make economic sense in other locations.