Alcatraz: lighting up the Rock
It used to be home to notorious criminals but now Alcatraz is the site of an ambitious renewable energy project.
The cell block stands empty of inmates. The likes of Al Capone, machine Gun Kelly and the Birdman of Alcatraz are long gone. It is now 50 years since Alcatraz was used as a federal prison. These days thousands of tourists are ferried across the 1.5 miles of San Francisco Bay to discover what life was like at The Rock.
Power for the craggy island has traditionally come from an ageing set of diesel generators, but last year the national Park Service (NPS) decided to install a renewable energy system to supply power to the island. Now a 307kW photovoltaic (PV) array sits on the roof of the main building, attached to two 2,000-amp-hour battery strings and an inverter plant.
The new 1,300-panel system produces close to 400,000kWh of electricity a year, reducing carbon dioxide (CO2) emissions by about 337,000kg a year and reducing the time the generator runs from 100 per cent to 40 per cent.
A massive solar battery system helps power the island when the sun doesn't shine – and it, too, is hidden from the view of the 1.4 million visitors the island and prison get each year.
The man responsible for ensuring that the project ran smoothly was Paul Cloyd, NPS engineer, who spoke to E&T about the project.
What prompted the decision to install solar panels at Alcatraz? Were other renewable energy options considered?
Prior to the PV system installation, the island used as much as 1200 gallons of diesel fuel per week to operate the diesel engine electrical generators. The diesel fuel must be on and off loaded to and from a tanker with a risk of a spill into the bay always a possibility.
Historically there had been a submarine electrical cable to the main land, but this was severed by a ship’s anchor in the 1950s. From the 1950s until the PV system came on line, all power to the island was provided by diesel-powered electrical generators. Those generators were not in compliance with the clean air standards required in the San Francisco Bay Area. The park received an Environmental Audit finding in 2008 (finding # 217) that the park was using more fuel annually than the permit with the Air Quality Board allowed. A new submarine cable was considered for this project to allow the PV system to feedback to the grid and allow complete elimination of generator use. However the project team determined the submarine cable was cost prohibitive. I believe at one time some talk of a wind mill came up, but was fairly quickly determined to be too intrusive to the historic site.
As part of the overall project new more efficient diesel generators have been installed. The generators provide power when PV or battery sources are insufficient. Under optimal conditions (clear weather & longer summer days) generator use has been reduced by more than 90 per cent.
Do you have to approach installing solar panels on historic buildings such as Alcatraz in any special way or the same as any commercial building?
For historic buildings and sites, during the design stage, the project team will consult closely with NPS cultural resource staff and the state historic preservation officer to ensure any impacts to the historic character are minimized if not eliminated.
How did you decide on the specification and individual components for the system?
We worked closely with NREL and a consulting firm, HDR, to determine the system requirements. These requirements were called out in the Request for Proposal (RFP) for a Design Build contract. After award during the design portion of the design build contract NPS reviewed and commented on multiple design submissions to ensure the system would meet our needs.
What were the biggest challenges in approaching the project?
We determined the roofing needed replacing prior to the installation of the array. The old built up roofing contained layer of asbestos felts. In addition as the roofing was removed we found in limited areas that the condition of the roof concrete slab required repair. Another challenge was the requirement to arrange the PV array around the historic architectural and mechanical features on the roof. This includes skylights and large roof mounted pipes. The consultant prepared a study to determine how best to place the panels to minimize the shadow impact from these features on the array. An unexpected challenge, we found that birds were attracted to the warmth of the PV panels. Bird droppings on the panels became a serious issue in the late summer when rain is less frequent and birds are more abundant. The project provided for means of washing down the panels. However but the frequency wash downs needed significantly exceeded expectations.
Where there any objects to such a highly visible building having solar panels?
Although the building is highly visible, the PV array installation is only visible either while one is on the roof itself or from the air. The State Historic Preservation Officer as well as the Park Cultural Resource staff was quite vigilant on the point of not being visible to the visiting public. Visitors are informed about the system via an electronic display kiosk showing the real time performance of the system. You may be able to see the array this summer when the America's cup yacht races are televised.
What about challenges in the installation itself as it is a very busy tourist site?
The staging and work areas were largely in areas not accessible to visitors. Materials were brought to the island early in the day, before visitation hours or late in the day after visiting hours. Construction debris removal occurred in the same time frames. The biggest challenge was during the power source switch over period.
Prior to the switch over the contractor attempted to tweak the system utilising simulated island grid loads. However, the real island grid load had constantly fluctuating load characteristics that proved impractical to accurately simulate.
Consequently during multiple attempts to switch the island grid load to the PV system source, the power quality caused problems, with flickering lights and sensitive electronic equipment jeopardised.
The team developed a protocol that before the system switch over attempt, the day before all staff were instructed to shut down all sensitive equipment at close of business. Then early the following morning, prior to visitors arriving, a system switch would be attempted.
If the system was found ‘glitchy’, then correcting tweaks to the system control software would be made. If the correction efforts were not successful, as visitor arrival time approached, then the decision would be made to stay on generator for the day so as not to disrupt visitor activities.
One set of sensitive of equipment pieces was the digital projects used for visitor presentations. The power fluctuation would cause very expensive and inconvenient to replace projector bulbs to fail. As the switch over process continued over several weeks these projector units were placed on their one back-up generators until the PV system was determined to be suitably reliable.
How important is battery storage to the installation?
So far the batteries have performance well. Even in the winter months the battery array typical provides island power after the sun has set for about 2/3 of the night. Once the batteries reached a set point of state of discharge then the generator kicks on to recharge them. The battery array is essential in minimising generator run time, a prime goal of the project.
How has the installation been performing?
Performance has been satisfactory. We are considering if the battery state of discharge set point is set too conservatively. This could result in more generator run time than need be especially in the winter. There are on-going control system software tweaks to better optimize battery use and system performance.
Are there plans to do the same to other landmarks, historic buildings?
We recently enlarged a PV array for a historic visitor centre at Death Valley National Park. These are located adjacent to the visitor centre in the vehicle parking areas. The panels function as shade structures while providing PV power.
Similarly we recently completed a ground mounted off building PV array for a historic visitor centre at Lake Mead National Recreation Area. I am not aware of other upcoming PV projects for historic buildings.
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