NW Wind & Solar: Seattle Aquarium Community Solar Project
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The Seattle Aquarium extends over the saltwater bay on Pier 59 in downtown Seattle. The historic landmark attracts almost 1 million visitors annually. In December 2013, NW Wind & Solar commissioned a 49.4 kW solar installation on the aquarium rooftop. The local utility, Seattle City Light, is sponsoring and will administer the Community Solar Program. The NW-based Bonneville Environmental Foundation provided technical support throughout the system design and installation.
While the Seattle Landmarks Preservation Board has special variances for solar, it required the aquarium to submit profiles, renderings and documents to ensure that the installation would be aesthetically pleasing and would not compromise the historical integrity of the landmark Seattle pier. The board approved the design, in part thanks to the glass-on-glass Silicon Energy modules, whose appearance exceeded the design architect’s expectations.
The array is subject to high wind and saltwater mist. The double-glass design of the Cascade Series SiE200 module makes it a good choice for marine environments. Silicon Energy also offers an aluminum conduit upgrade for its powder-coated wire management and mounting system, specifically for marine installations. Anodized aluminum SunEarth Solar Strut provided added insurance that rust and corrosion would not compromise the looks of the landmark structure.
Interconnecting the system to a building that Seattle City Light’s downtown secondary network supplies proved to be a challenge. In most cases, commercial PV installations tie into the building’s electrical distribution system, which a utility radial distribution feeder line in turn supplies. However, a secondary network distribution system, interconnected to multiple radial feeder lines, feeds the Seattle Aquarium. The location of the aquarium’s electrical service—immediately adjacent to a secondary network transformer—is just about the worst-case scenario for the point of interconnection. A 12.47 kV feeder through the secondary network feeds the aquarium, and it has a 277/480 3-phase service, requiring a step-down transformer to interconnect the 208 Vac Silicon Energy inverters.
For this type of electrical service configuration, utilities may have concerns about backfeeding from the PV array to the secondary network. Bonneville Environmental Foundation, NW Wind & Solar and Seattle City Light sought the help of consultants from Schweitzer Engineering Laboratories to address the interconnection concerns. They determined that if the aquarium demand were to drop below 3 times the dc rating of the PV system, the system would require a minimum import relay controlling a contactor to disconnect the PV system and protect the secondary network from backfeeding. Designers configured the system to automatically disconnect if the aquarium’s instantaneous power demand ever drops below 150 kW, a rare situation that might occur if the seawater pumps shut down.
“Many stakeholders were involved in the Seattle Aquarium Community Solar Project. This led to several design and installation challenges that made for an exciting and memorable installation. The final product is durable, aesthetically pleasing and highly visible from Seattle’s waterfront. It’s a symbol of Washington’s ongoing commitment to local renewable energy.”
—Kevin Charap, division manager, NW Wind & Solar
“Community Solar demonstrates Seattle City Light’s commitment to meeting the energy needs of our customers in an environmentally sustainable manner and shows why we call ourselves ‘The Nation’s Greenest Utility.’”
—Sephir Hamilton, chief of staff, Seattle City Light
INSTALLATION FIRM: NW Wind & Solar
DATE COMMISSIONED: December 2013
INSTALLATION TIME FRAME: 45 days
LOCATION: Seattle, WA, 47.6°N
SOLAR RESOURCE: 3.7 kWh/m2/day
ASHRAE DESIGN TEMPERATURES: 70°F 2% average high, 27°F extreme minimum
ARRAY CAPACITY: 49.4 kWdc
ANNUAL AC PRODUCTION: 54,023 kWh
MODULES: 247 Silicon Energy Cascade Series SiE200, 200 W STC, +3/-3%, 7.8 Imp, 25.6 Vmp, 8.4 Isc, 30.6 Voc
INVERTERS: 277/480 Vac service, two Silicon Energy SiE3840 (3.3 kW at 208 Vac, 600 Vdc maximum input, 220–550 Vdc input voltage range), eight Silicon Energy SiE5300 (4.6 kW at 208 Vac, 600 Vdc maximum input, 220–550 Vdc input voltage range)
ARRAY: 14 modules per source circuit, typical (2,800 W, 7.8 Imp, 358.4 Vmp, 8.4 Isc, 428.4 Voc), 18 source circuits total, 49.4 kW array total
ARRAY INSTALLATION: Roof mount, composite shingle roofing, SunEarth 2.5-inch Black Anodized Solar Strut, Silicon Energy Cascade Series mounting system, 180° azimuth, 27° tilt
SYSTEM MONITORING: DECK Monitoring