The Rock, once home to notorious criminals, now hosts 1,300 solar panels to provide the tiny island with power.
Once the home of such criminal luminaries as Al Capone and Machine Gun Kelly, the craggy island one and a half miles off the coast of San Francisco has been a fort, a federal prison and latterly a tourist attraction. Alcatraz, or ‘The Rock’ to give it its common moniker, was closed as a prison 50 years ago.
1. Long gone are the notorious inmates. Today, Alcatraz is home to 1,300 solar panels in place of the diesel generators that powered the island for over 75 years. Although the building is highly visible, the photovoltaic (PV) array installation is only visible from the air.
2. On the roof of the main cell house, a 307kW PV array capable of producing 400,000kWh of electricity each year reduces the carbon dioxide emissions by around 337,000kg a year. The roofing needed replacing prior to installation because the old one contained layers of asbestos felts.
3. There have been numerous silver screen adaptations of events on the island, one of the most popular, ‘Birdman of Alcatraz’, seeing Burt Lancaster as Robert Stroud, the ‘Birdman’. Stroud (inset) spent 53 of his 72 years behind prison bars. He was permitted to keep birds in his cell and maintain a laboratory. From studies conducted in his cell, he produced ‘Stroud’s Digest of Diseases of Birds’, considered by many ornithologists to be a definitive work on bird sicknesses.
4. When the prison closed in March of 1963 its incumbents were transferred to other Federal prisons.
5. The PV array is connected to two 2,000-amp-hour battery strings and an inverter plant, and more efficient diesel generators were installed. The generators provide power when PV or battery sources are insufficient. Under optimal conditions, generator use has been reduced by more than 90 per cent.
6. Even in the winter months the battery array typically provides island power for about two-thirds of the night. Once the batteries have reached a set point of state of discharge, the generator kicks on to recharge them.
7. Another challenge was the requirement to arrange the PV array around the historic architectural and mechanical features of the roof. This includes skylights and large roof-mounted pipes. An unexpected challenge was that birds were attracted to the warmth of the panels and their droppings became a serious issue in the late summer when rain is less frequent and birds are more abundant. The project provided a way of washing down the panels but the frequency at which wash downs were needed significantly exceeded expectations.