Escape from the grid: Alcatraz goes solar

The decision to move the San Francisco Bay island of Alcatraz off-grid was not, initially, one made by choice. It was reached through necessity several years ago, when the notorious former prison’s access to Pacific Gas & Electric’s electric grid was severed, accidentally, by a ship’s anchor. As Pike Research analysts Peter Asmus writes, back then diesel generators were installed to provide power for the now hugely popular tourist destination. But, “as the price of diesel began to climb, and the cost of solar PV fell, developing a state-of-the-art microgrid appeared attractive.”

In this way, Alcatraz could serve as a microcosm of the unfolding global clean energy revolution, which appears most likely to see the biggest shifts away from traditional power sources, and towards distributed and clean energy sources, come not from choice but, in the end, through necessity: because it will make more sense for households, businesses, cities and countries – and it will be cheaper.

For Alcatraz, the answer seemed clear: build a microgrid, with a 307kW solar array with a deep-cycle battery back-up unit, as well as a back-up diesel generator. The installation of the the 1,300 SunPower solar panels at Alcatraz was the result of a collaboration between America’s National Parks Service (NPS) and the US DoE and the National Renewable Energy Laboratory (NREL), with funding via a $3.6 million cash stimulus from the American Reinvestment and Recovery Act.

According to the NREL, the solar array will power lights and appliances and generate close to 400,000kWh of electricity a year. Kept clean, says Asmus, the PV panels can meet the entire island’s power supply, “even during San Francisco’s famous fog, which reduces potential output by more than half.” Energy Matters reports that so far, the prison has cut CO2 emissions by around 337,000kg a year and has been able to slash generator hours by 60 per cent, thanks to a 2,000-amp-hour deep cycle battery bank and other energy efficiency measures.

The technology that forms the backbone of the microgrid installed on Alcatraz comes from Princeton Power Systems, a smart inverter company based in Princeton, New Jersey. Pike’s Asmus, who went to the island at Princeton’s invitation, notes that recent advances in inverters for solar PV and small wind turbines are setting the stage for a viable microgrid market to evolve.

“New inverters allow for safe islanding – i.e., the creation of small distribution systems cut off from the larger power grid,” Asmus says. “When connected to the larger grid, inverters enable distributed renewable resources, such as solar PV, to continue to operate when the larger grid goes down, thus avoiding the feeder fault concerns associated with synchronous generators, which may take 2, 5, or even 10 seconds to respond to a grid outage.” (And he notes that Pike Research’s new report, Inverters for Renewable Energy Applications, forecasts that the total inverter market will surpass $4 billion in global revenues by 2018.)

Asmus writes that on the day of his visit, the entire island was running on diesel generation, with back-up from the batteries, because the solar array was not working because a switch had failed. “That’s the beauty of a microgrid,” he says, “a diversity of resources can run together or serve as back-up to each other.

Meanwhile, a solar-powered Alcatraz is saving money. Andy Walker, a senior engineer from the DoE, tells EnergyMatters that the solar array on the roof of the prison’s cellhouse block is cutting costs on fuel that would otherwise have to be transported by boat from the mainland.

“The cost of transporting diesel fuel to the island (maintenance costs and the price of the fuel itself) boosted the cost of electricity for the island to about 76 cents a kilowatt-hour. The PV project brings that cost to 71 cents a kilowatt-hour, and that includes the capital costs of buying the solar panels and erecting them on roofs.”