Joule Energy: Old Alabama Road 2
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Located in Woodland, Georgia, the Old Alabama Road 2 (OAR 2) solar project represents two trends present in many megawatt-scale ground-mounted PV installations—tracked arrays and the use of string inverters for power processing. The OAR 2 project team has three primary stakeholders: Boviet Solar, a subsidiary of Powerway Group, is the system owner and module vendor; Hecate Energy served as the project developer; and New Orleans–based Joule Energy was the project EPC firm.
Site grading began in late September 2016. Construction coincided with a significant drought that impacted much of western Georgia, and the drought conditions complicated early construction efforts. At one point in the site preparation process, the grading contractor was not able to secure burn permits. As a result, workers had to truck vegetation debris off-site, which added unanticipated cost and resulted in a minor project delay. Another early delay resulted from the severing of an unmapped 2-inch gas line during stump excavation. Further investigation revealed that the pipe had been abandoned and supposedly capped off many years ago. The project team worked with local officials to trace the source of the pipe and make the appropriate repairs quickly and safely.
With site preparation completed, Joule Energy opted to subcontract the tracker and module installation, focusing its efforts on realizing the cost savings that optimizing the ac power collection system would offer. Considerations included the strategic location of power processing equipment and ac aggregation panels, as well as approaches to minimize the project’s wiring material cost and speed conductor deployment. A total of 35 Ginlong Solis 40 kW 3-phase string inverters provides power conversion and optimization for OAR 2.
All array rows contain even numbers of tracker tables, which simplified the wiring plan. This configuration allowed Joule Energy to parallel two module source circuits and thereby minimize homerun wiring back to the string inverters. Joule developed a relatively simple homerun gauge scheme based on each string’s position in its row. For shorter runs, it used 10 AWG and 8 AWG conductors; for longer runs, it stepped conductor size up to 6 AWG. Installers paralleled strings using Y-branch connectors for 10 AWG and 8 AWG conductors and Tyco GTAP connectors for 6 AWG conductors.
Joule Energy used the leapfrog wiring method shown in SolarPro’s April/May 2014 issue. This wiring configuration results in the collocation of each source circuit’s homerun connections, which allowed OAR 2 installers to plug them directly into the parallel branch connector. The installation team ran all homerun conductor pairs to their respective inverter-input terminals with no intermediary breaks. This approach complicated the initial installation, particularly because the design called for direct burial of portions of each homerun. However, the design also significantly reduced the number of field-installed connections, which are among the Joule Energy O&M team’s most frequently cited failure concerns. Because only two strings terminate at each inverter MPP tracker, the system did not require any in-field fuses, which further cut costs and simplified installation.
The installation team had to learn quickly how to deploy both large-gauge wire spools and large numbers of smaller-gauge spools. In early attempts, team members used an extendable-reach forklift and a custom-built lumber rack. The Joule Energy team has since learned that a more optimal approach is to use a full flatbed trailer with turntables underneath the spools, a setup it purchased for future projects.
Installers grouped the inverters at the site location nearest to the point of interconnection. They constructed two separate equipment walls, one comprising inverters serving the eastern rows of the array and one comprising inverters serving the central and western rows of the array. The equipment support structures include metal roofing panels along the top and back sides of the structure to shade the inverters. The 11 inverters on the eastern equipment wall combine at an 800 A breaker panel, as do each of the two sets of 12 inverters on the central and western equipment wall. Joule Energy minimized ac voltage drop by locating each inverter within 40 feet of its respective breaker panel, and the breaker panels within 120 feet of the system’s fused disconnects.
“While this project is relatively small in size compared to many of today’s solar farms, it represented a big accomplishment for our team. We applied a fresh perspective to the overall EPC process—focusing on design and installation efficiencies—and produced a showcase system that serves as the standard for our current and future work.”
—Corey Shalanski, Joule Energy
DESIGN & INSTALLATION LEAD: Corey Shalanski, senior PV engineer, Joule Energy
DATE COMMISSIONED: April 2017
INSTALLATION TIME FRAME: 40 days
LOCATION: Woodland, GA 32.8°N
SOLAR RESOURCE: 4.59 kWh/m2/ day
ASHRAE DESIGN TEMPERATURES: 95°F 2% average high, 12.2°F extreme minimum
ARRAY CAPACITY: 1.613 MWdc
ANNUAL AC PRODUCTION: 2,826 MWh
MODULES: 5,040 Boviet Solar BVM6612P-320, 320 W STC, +5/-0 W, 8.65 Imp, 37 Vmp, 9.17 Isc, 45.5 Voc
INVERTERS: 3-phase 277/480 Vac service, 35 Ginlong Technologies Solis-40K-US, 1,000 Vdc maximum input, 200 Vdc–800 Vdc MPPT range
ARRAY: 18 modules per source circuit (5,760 W STC, 8.65 Imp, 666 Vmp, 9.17 Isc, 819 Voc), eight source circuits per inverter (inverter 46.08 kW, 69.2 Imp, 666 Vmp, 73.36 Isc, 819 Voc), array total 1.613 MWdc
ARRAY INSTALLATION: GameChange Solar Genius Tracker, single axis, independent row, 90° standard rotational range (104° range option), Zigbee wireless network
INVERTER AGGREGATION PANELS: Three 800 A panels with 800 A disconnects (two disconnects fused at 750 A and one fused at 700 A)
SYSTEM MONITORING: Locus Energy monitoring and analytics