Islands face a double threat in our warming world. Rising seas threaten to sweep them from the map; dependence on the fossil fuels largely responsible for those rising seas exposes island populations and economies to increasingly burdensome energy costs.
Until recently, Alcatraz Island, perched 1.5 miles from Fisherman’s Wharf in San Francisco Bay, could not operate without imported fuel. When I toured the island with National Park Service (NPS) staff in August 2010, Jim Calvinperez, the facilities manager and chief engineer, told me that 2,000 gallons of diesel fuel had to be shipped to the island weekly in order to keep the generators in the power plant humming.
The Golden Gate National Recreation Area, the NPS unit that manages Alcatraz, used $3.6 million from the American Recovery and Reinvestment Act (ARRA) to install a solar-powered microgrid on the island. The National Renewable Energy Laboratory’s Bill Scanlon recently published an overview of the project.
Engineers at NREL’s Federal Energy Management Program assisted the Park Service in designing the system, which included installation of a 307-kilowatt (kW) photovoltaic array atop the roof of the main Cellhouse building. Surplus electricity generated by the solar panels at peak is sent to a 2-megawatt-hour (MWh) valve-regulated lead-acid (VRLA) battery pack, which was installed next to the island’s new power plant.
A smart inverter system installed by Princeton Power Systems converts the direct current (DC) generated by the solar panels into alternating current (AC) used to power lighting and appliances and balances the fluctuating output of the PV panels with battery storage and diesel generators to meet the island's load. The microgrid comprises eight 100-kW grid-tied inverters, the rooftop PV array, the lead-acid battery pack, backup diesel generators, and a Web-based monitoring and control system. Pike Research’s Peter Asmus recently toured Alcatraz at the invitation of Princeton Power Systems and wrote afterward about the island’s microgrid.
The PV is capable of supplying all of the island’s electricity demand (Jim Calvinperez told me the island’s typical load is 90 to 120 kilowatt-hours). Over a year, the solar-powered microgrid will reduce the running time of the diesel generators from 100% to 40%.
The project was a long time in coming. As far back as 1995, NREL engineers were enlisted to assess the solar potential on Alcatraz and mock up what solar installations would look like to viewers on and off the island. The NPS had contracted the Sacramento Municipal Utility District (SMUD) to install PV on the island’s New Industries Building. In the end, aesthetic concerns prevented the project from moving forward.
The Park Service also looked into re-establishing a link to the electrical grid in San Francisco. My NPS guides told me that an anchor had severed the transmission link to the mainland just before the island’s prison closed in 1963. Alcatraz re-opened, years later, as an historic site managed by the NPS with the diesel-powered grid. A feasibility study conducted by researchers at the University of Washington indicated that installing an undersea transmission cable to San Francisco would be too costly.
The solar plans were shelved, awaiting funding. In the summer of 2009, when the Park Service learned of the availability of the ARRA funding, the project was re-launched. Over time, the project will save taxpayers money. Andy Walker, an NREL engineer who led the design assistance team for the project, told Bill Scanlon that before the solar-powered microgrid system was installed, the Park Service paid $0.76 per kWh for electricity on Alcatraz. The cost to taxpayers today is $0.71 per kWh, which includes the capital costs of buying and installing the rooftop PV system.
