A microgrid goes to jail [photos]


Chevron has built a microgrid at a jail in Dublin, Calif. in an effort to make sure energy doesn’t escape the 1 million square-foot facility east of San Francisco. Chevron and political dignitaries gathered on Thursday to unveil this microgrid at the Santa Rita Jail, which features solar, wind, fuel cell and a lithium-ion battery system.

Microgrids are sectioned off grids that can be independent from the larger electric grid and can often generate, use and store their own power. Microgrids are useful because they can provide their own energy long enough to deal with unexpected events such as power outages. The microgrid concept has become more appealing as more energy storage and power generation technologies have become more available and cheaper.

Santa Rita jail has 19 housing units for up to 4,000 inmates. The jail also runs a big kitchen operation: it prepares 12,000 meals per day, and some are shipped to other detention centers in the county. The jail needs 3 MW of constant power.

Santa Rita didn’t add all of its power generation equipment at the same time. It started with a 1.2 MW rooftop solar system featuring BP solar panels in 2002. Then it added a 1 MW fuel cell system from FuelCell Energy in 2005 and five turbines of 2.3KW each from Southwest Windpower in 2010.  In the past few months, 2 MW of lithium-ion batteries from BYD and 275 KW of Solaria solar panels that sit on trackers were brought online. Chevron oversaw the installations for all these except the Solaria systems.

The jail also is adding a solar thermal water heating system from Focal Point Energy, a winner of the 2008 California Clean Tech Open, that should be completed by May this year, said Matthew Muniz, energy program manager for Alameda County.

What ties all these power generation equipment and create the microgrid is the battery system, which can provide 4 MWh of energy, and a control system that figures out automatically when to bank or withdraw power from the batteries, said Eduardo Alegria, a power system engineer at Chevron Energy Solutions. There also is an equipment that disconnects the jail’s own distribution network from the local utility grid (run by Pacific Gas & Electric) when there is a blackout.

The ability to store power, including charging the batteries at night when power is cheap, and to disconnect from the PG&E grid, are key measures to create the microgrid at the jail. Banking power when it’s cheap and using it when it’s not will save the jail about $100,000 pear year, Alegria said.

In the past, the fuel cell and rooftop solar systems would shut down when there was a blackout because they were tied to the grid, which would prompt power generation equipment to go offline during a blackout so that utility workers could work on repairing equipment without being electrocuted. That meant the jail would have to turn on diesel generators to provide backup power even though it could’ve just continued to run the fuel cell system, which produces power as long as it gets fed natural gas, or gotten power from the solar panels during daylight.

The microgrid set up allows the jail to supply its own power for up to eight hours. The more recent installations of wind turbines, battery and its control system and solar thermal water heating equipment cost around $11.7 million, Muniz said. The county owns the equipment.



Let’s see…..saves 100,000 a year and costs over 11 million. Interest on 11 million, even at 2%, is 200,000 per year, so the payback for this innovative system is ????

Ucilia Wang

The $100K/yr only accounts for battery-related energy savings. The baseload power production by the fuel cell and the energy from solar/wind/thermal aren’t factored in. If I get some good numbers, I’ll add them in.

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