“While this project is relatively small in size compared to many of today’s solar farms, it represented a big accomplishment for the team. A fresh perspective was applied to the overall EPC process focusing on design and installation efficiencies and produced a showcase system that serves as the standard for the current and future work.”—Corey Shalanski, Joule Energy
Located in Woodland, Georgia, the OldAlabama Road 2 (OAR 2) solar projectrepresents two trends present in manymegawatt-scale ground-mounted PVinstallations—tracked arrays and the useof string inverters for power processing.The OAR 2 project team has three primarystakeholders: Boviet Solar, a subsidiaryof Powerway Group, is the system ownerand module vendor; Hecate Energyserved as the project developer; and NewOrleans–based Joule Energy was the projectEPC firm.
Project team:EPC joule energy, joule-energy.com; owner - Boviet solar USA, bovietsolarusa.com; developerhecate energy, hecateenergy.com
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 extrememinimum
Array capacity: 1.613 MWdc
Annual AC production:2,826 MWh
Site grading began in late September2016. Construction coincided witha significant drought that impactedmuch of western Georgia, and thedrought conditions complicated earlyconstruction efforts. At one point inthe site preparation process, the gradingcontractor was not able to secureburn permits. As a result, workers hadto truck vegetation debris off-site, whichadded unanticipated cost and resultedin a minor project delay. Another earlydelay resulted from the severing ofan unmapped 2-inch gas line duringstump excavation. Further investigationrevealed that the pipe had been abandonedand supposedly capped off manyyears ago. The project team worked withlocal officials to trace the source of thepipe and quickly and safely make theappropriate repairs.
With site preparation completed,Joule Energy opted to subcontract thetracker and module installation, focusingits efforts on realizing the cost savingsthat optimizing the ac power collectionsystem would offer. Considerationsincluded the strategic location of powerprocessing equipment and ac aggregationpanels, as well as approaches tominimize the project’s wiring materialcost and speed conductor deployment. Atotal of 35 Ginlong Solis 40 kW 3-phasestring inverters provides power conversionand optimization for OAR 2.
All array rows contain even numbersof tracker tables, which simplifiedthe wiring plan. This configurationallowed Joule Energy to parallel twomodule source circuits and therebyminimize homerun wiring back to thestring inverters. Joule developed a relativelysimple homerun gauge schemebased on each string’s position in itsrow. For shorter runs, it used 10 AWGand 8 AWG conductors; for longer runs,it stepped conductor size up to 6 AWG.Installers paralleled strings using Ybranch connectors for 10 AWG and8 AWG conductors and Tyco GTAP connectorsfor 6 AWG conductors.
Joule Energy used the leapfrog wiringmethod. This wiring configurationresults in the colocation of each sourcecircuit’s homerun connections, whichallowed OAR 2 installers to plug themdirectly into the parallel branch connector.The installation team ran all homerunconductor pairs to their respectiveinverter-input terminals with no intermediarybreaks. This approach complicatedthe initial installation, particularlybecause the design called for direct burialof portions of each homerun. However,the design also significantly reduced thenumber of field-installed connections, which are among the Joule Energy O&Mteam’s most frequently cited failureconcerns. Because only two strings terminate at each inverter MPP tracker, thesystem did not require any in-field fuses,which further cut costs and simplifiedinstallation.
The installation team had to learnquickly how to deploy both large-gaugewire spools and large numbers ofsmaller-gauge spools. In early attempts,team members used an extendablereachforklift and a custom-builtlumber rack. The Joule Energy teamhas since learned that a more optimalapproach is to use a full flatbed trailerwith turntables underneath the spools,a setup it purchased for future projects.
Installers grouped the inverters atthe site location nearest to the pointof interconnection. They constructedtwo separate equipment walls, onecomprising inverters serving the easternrows of the array and one comprisinginverters serving the centraland western rows of the array. The equipment support structures includemetal roofing panels along the top andback sides of the structure to shadethe inverters. The 11 inverters on theeastern equipment wall combine at an 800 A breaker panel, as do each of thetwo sets of 12 inverters on the centraland western equipment wall. JouleEnergy minimized ac voltage drop bylocating each inverter within 40 feet ofits respective breaker panel, and thebreaker panels within 120 feet of thesystem’s fused disconnects.
“While this project is relatively small insize compared to many of today’s solarfarms, it represented a big accomplishmentfor the team. A freshperspective was applied to the overall EPC processfocusing on design and installationefficienciesand produced a showcasesystem that serves as the standard forthe current and future work.”—Corey Shalanski, Joule Energy
Modules: 5,040 Boviet SolarBVM6612P-320, 320 W STC, +5/-0 W,8.65 Imp, 37 Vmp, 9.17 Isc, 45.5 Voc
Inverters: 3-phase 277/480 Vacservice, 35 Ginlong TechnologiesSolis-40K-US, 1,000 Vdc maximuminput, 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 sourcecircuits per inverter (inverter 46.08 kW,69.2 Imp, 666 Vmp, 73.36 Isc, 819Voc), array total 1.613 MWdc
Array installation:GameChangeSolar Genius Tracker, single axis,independent row, 90° standardrotational range (104° range option),Zigbee wireless network
Inverter aggregation panels:Three 800 A panels with 800 Adisconnects (two disconnects fused at750 A and one fused at 700 A)
System monitoring: Locus Energymonitoring and analytics
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