Alcatraz: The Ultimate Solar+Storage Microgrid

While at Intersolar, I had the opportunity to take a tour of Alcatraz Island—not of the touristed parts, but rather of the solar generation and storage facilities that tourists rarely see, let alone even know exists.

Few people realize that Alcatraz has been mainly powered by PV since 2012. There is no connection to the grid in San Francisco just across the bay. Prior to the installation of the array, 2,000 gallons of diesel fuel were ferried to the island each week, where it fed large generators. Alcatraz-Rooftop-Solar-Array Today, two diesel generators remain for backup power generation, but the island is primarily powered by 959 SunPower modules on the roof of the main cellhouse building.

San-Francisco-Skyline-from-Alcatraz-Rooftop-1The array is rated for 307 kW. It feeds Princeton Power Systems inverters and a large bank of Deka lead-acid batteries.

Deka-Battery-Bank-on-Alcatraz

Princeton-Inverters-on-Alcatraz

The inverters and battery bank are stored in an old building that’s now off-limits to visitors:

House The typical load on the island varies between 50 and 80 kW, and the array produces a peak of 175 kW a day; the batteries absorb the excess power generated. Even so, the array and stored battery power is only enough to power 60% of the island’s loads, so the two diesel power generators (image below) make up for the rest.

Diesel-Generators-on-AlcatrazThe whole system cost $3.6 million and was funded by the American Reinvestment and Recovery Act, which also brought us the Investment Tax Credit for solar.

The thing that really stood out for is how much more wind power would have made sense for Alcatraz. I’m no wind expert, but a few factors jumped out at me.

First, San Francisco is notoriously cloudy and foggy most of the year. (The day I was there was atypically beautiful.) Relying on the sun for a major tourist attraction’s power thus seems like a risky proposition. Even with a 307 kW array and a relatively modest load, those diesel generators still need to be fired up occasionally, which means diesel fuel still needs to be ferried to the island as it was decades ago.

Second, San Francisco—especially the Bay—is notoriously windy. The wind rarely calms down. The sun, obviously, is never available at night

And finally, bird poop is a serious problem for the array. Seagulls love Alcatraz, and those modules are a prime target. The National Park Service has to clean them frequently. Wind turbines are immune from this problem, and the turbine might scare away the seagulls, anyway. Of course, the seagulls would need to find another place to nest, so there would be an environmental impact to address.

Bird-Poop-on-Alcatraz-Solar-Array

I don’t know if wind turbines were even considered, but I do know that parties advocating for historical preservation objected to the array unless it could be kept out of site. So, they surely would have gone to town on a proposal to have tall wind turbines, even though Alcatraz is perhaps the perfect place for them.

Tower-on-Alcatraz

Check out this video, made by Intersolar in 2014, which has some great footage of the system:

All photos taken by David K. Wolpert on an iPhone 5s.

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