Alpha Energy, ET Capital and Geenex: HXOap Solar Farm

A landmark project for the East Coast and North Carolina, the 29.7 MWdc HXOap Solar Farm is built on the site of the decommissioned Halifax County Airport. At the time of commissioning, the project is the largest PV system in North Carolina, one of the largest on the East Coast and the single largest string inverter system in the western hemisphere. The project’s decentralized architecture features 866 Advanced Energy 3-phase 1,000 Vdc non-isolated string inverters.

Geenex, a Charlotte, North Carolina–based solar developer, and ET Capital, a California-based energy investment company and subsidiary of ET Solar Group, developed the HXOap Solar Farm in partnership. Alpha Energy, a member of the Alpha Group, provided engineering consultation and construction. Upon completion, Duke Energy will acquire the project and sell the energy generated to Dominion over the 15-year PPA. The project created more than 150 jobs during peak construction and will inject an estimated $75 million into the economically challenged Halifax County between 2014 and 2029.

The system uses RBI Solar’s fixed-tilt GM-I mounting system in conjunction with driven-post foundations to mount 98,724 ET Solar modules in two-module-high portrait orientation at an azimuth of 180° and a 20° tilt. The power conditioning system employs 866 23.2 kWac Advanced Energy AE 3TL string inverters. A standardized array layout connects each inverter to subarrays consisting of 19 modules per source circuit with six strings per inverter. The placement of each inverter, ac panel and transformer pad creates a consistent and optimized design. Each of the 149 ac panels aggregates the output of either five or six string inverters. The design distributes inverters, switchgear and transformers strategically throughout the array field. The overall dc and ac ohmic losses for the system are 0.23% and 2.39%, respectively.

The 20 MWac power conversion system is organized into 10 blocks total, with seven blocks dedicated to a 15 MWac collection system and three blocks dedicated to a 5 MWac collection system. The 15 MWac collection section consists of seven pads —each with one 2 MVA 34.5 kV Cooper transformer and two Eaton switchboards—and interconnects at a 34.5 kV medium-voltage connection. This interconnection point is located at the southernmost section of the 15 MWac subarray. The 5 MWac collection system  utilizes three pads, of which two have one 13.2 kV 2 MVA Cooper transformer and two Eaton switchboards; the remaining pad has one 13.2 kV 700 kVA Cooper transformer and a single Eaton switchboard. Both the 34.5 kV interconnection point and the 13.2 kV interconnection point lead to Dominion’s Homertown substation.

“Alpha Energy is proud to be the first EPC in the US to construct a string-level distribution system of this magnitude. Watching 866 Advanced Energy inverters communicating on our network is impressive.”

Ronnie Andrawis, Alpha Energy

“This AE 3TL project is a great example of the inflection point in the market towards 3-phase string technology.”

Bates Marshall, VP of Global Sales and Marketing, Advanced Energy


DEVELOPERS: ET Capital,; Geenex,

DESIGNERS: Mike Doman, engineering consultant, Alpha Energy,; Dominic Lopez, senior project manager and system engineer, ET Capital

LEAD INSTALLER: Ronnie Andrawis, senior project manager, Alpha Energy



LOCATION: Roanoke Rapids, NC, 36.5°N

SOLAR RESOURCE: 5 kWh/m2/day

ASHRAE DESIGN TEMPERATURES: 93°F 2% avg. high, 10°F extreme min.



Equipment Specifications

MODULES: 98,724 modules total; 81,738 ET-P672300, 300 W STC, +5/-0 W, 8.18 Imp, 36.68 Vmp, 8.72 Isc, 44.89 Voc; 16,986 ET-P672305, 305 W STC, +5/-0 W, 8.21 Imp, 37.18 Vmp, 8.78 Isc, 45.12 Voc

INVERTERS: 866 Advanced Energy AE 3TL-23, 23.2 kW, 1,000 Vdc maximum input, 250–900 Vdc MPPT range, non-isolated 3-phase 480 Vac nominal output, 98% CEC efficiency; 13.2 kV and 35.4 kV medium-voltage interconnections

ARRAY: Nineteen modules per source circuit (for ET-P672300: 5,700 W, 8.18 Imp, 696.9 Vmp, 8.72 Isc, 852.9 Voc), six strings per inverter (for ET-P672300: 34.2 kW, 49.08 Imp, 696.9 Vmp, 52.32 Isc, 852.9 Voc), 866 inverters total, 29.7 MWdc array capacity total, 1.5 dc-to-ac ratio

ARRAY INSTALLATION: Fixed-tilt ground mount, driven posts, RBI Solar GM-I mounting system, 180° azimuth, 20° tilt

SYSTEM MONITORING: Cisco Switches with AlsoEnergy monitoring hardware and software

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