When the Village of Oak Park, Ill., commissioned a PV system for the Avenue Parking Garage, it didn’t intentionally set out to win any awards. However, the array’s exceptional design, which was not without its challenges, made it a shoe-in for the 2013 Project of the Year Award (Structures Less than $5 Million) from the American Public Works Association (APWA) Chicago Metro Chapter and has since been nominated for an APWA national award.
The 99.5-kW PV system, one of the largest municipality-owned solar arrays in Illinois, is located on the sixth floor of the Avenue Parking Garage, providing power throughout the facility and its electric vehicle charging stations. Solar Service Inc., based in Niles, Ill., designed and installed the system, which comprises 390 SolarWorld SW255 Mono modules and 12 SMA inverters (six Sunny Boy 6000-US and six Sunny Boy 8000-US).
SMA Sunny Boy inverters were selected over a single central inverter to allow for ease of installation and maintenance and providing monitoring granularity. “For commercial system designs, I always prefer multiple inverters so performance can be compared and production issues easily assessed via remote or onsite monitoring,” said Garrison Riegel, system designer and project manager for Solar Service. “The decentralized design provides improved energy harvest and by using string inverters we maximized cost-effectiveness and long-term system reliability. We chose SMA Sunny Boys for this project specifically because they have proven to be one of the most reliable string inverters available.”
Safety and Structure
The main challenge was creating a PV system design that would maximize performance and longevity, but not compromise the integrity of the existing parking garage structure. The safety of the general public and protecting the racking from damage were also primary design factors. While these considerations are similar for all installations, this project posed certain challenges seen in areas prone to harsh winters, such as protecting the racking’s support posts from possible snowplow damage.
To combat some of these issues, pole mounts and cantilevered carport-type racking systems were initially considered. However, “the reaction to the environmental stresses placed on these types of rack designs would have compromised the garage’s structural integrity unless we made significant structural reinforcements,” said Mark Tryon of Larson Engineering, who worked on the project. In the end, a canopy racking system design with a custom galvanized steel frame and IronRidge XRS rails was chosen, thereby eliminating the need for structural reinforcement of the garage.
Blending seamlessly into the aesthetic and function of the parking garage was important for the system’s final design. To keep its upright posts away from vehicles and snow plows, the 50-ton steel racking system was anchored to the parking garage’s elevated support columns. The array was installed at a single slope–at a similar angle to the adjacent garage ramp—with two gaps that allow for expansion and contraction of the aluminum rails, as well as access points for maintenance and cleaning as necessary.
Now that the system has been commissioned, it has exceeded the initial energy estimations by the National Renewable Energy Laboratory’s PVWatts™ calculator by as much as 25 percent and is expected to produce about 110,000 kWh annually, earning it rave review from city officials and possibly even a few more awards in the future.
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