NRG Renew: MGM Resorts International, Mandalay Bay
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Phase I of the Mandalay Bay PV plant has a total capacity of 6.4 MWdc and utilizes approximately 850,000 square feet of the Mandalay Bay Conference Center’s 950,000-square-foot roof area. The system is designed to the 2012 IBC and NEC 2008 per Clark County Codes in May 2014, when the designer submitted the permit application for review and approval.
Sunora Energy Solutions deployed the array on Unirac’s RM roof-mount system, secured by 49,026 ballast blocks (32 pounds each) and 4,310 anchors hot-welded to the surface TPO membrane to satisfy uplift load requirements. There are no mechanical attachments between the racking system and the buildings’ steel structures. Sunora installed the roof-mounted inverter aggregation switchboards and oil-filled transformers on steel racks mechanically attached to the building’s main columns and beams.
This project is unique in that the installers positioned the dc and ac electrical equipment that supports the PV plant on the roof adjacent to the PV arrays. This electrical equipment includes the string inverters, panelboards, switchboards and a DAS system, plus three 1 MVA and one 1.5 MVA transformers. A 12 kVA medium-voltage collection system delivers ac output power to new switchgear on the ground floor. The point of interconnection is approximately 3,800 feet from the switchgear, at one of the main electrical service points between NV Energy (NVE) and Mandalay Bay.
A challenging aspect of the project is that no PPA is in place with NVE. Contractually, all solar-generated power must be delivered to and used by the Manadalay Bay property. For this reason, the project team installed multiple safeguards to ensure that the PV system will not backfeed into NVE’s system. The solution includes a Kirk Key system located at both the designated solar plant switchgear and the main NVE interconnection point to the Mandalay Bay facility, which ensures that no one can open the main NVE breaker without opening the solar breaker first. In addition, a relay and communication system measures the Mandalay Bay facility load and the solar power output. If the PV system output reaches 92% of the total load, a curtailment feature in the relay system forces an automatic reduction in power output. Any issues that occur trigger alarms, and NVE, NRG and Mandalay Bay can use the relay control to remotely limit plant output. The inverter software also features a curtailment function that a system manager can use remotely if power generated is reaching power usage levels. Based on the load profiles and expected output of the solar arrays, NRG anticipates that curtailment will not be necessary in the life of the system.
“The MGM Phase I and Phase II solar projects at the Mandalay Bay Convention Center make use of the world-class Nevada solar resource and allow Mandalay Bay to generate a significant portion of the convention center’s electrical load. With an expected Phase II completion date of November 2015 and an installed capacity of 8.8 MWdc, the two projects combined will comprise one of the largest rooftop solar arrays in the US.”
—Randall Hickok, senior vice president, asset management and engineering, NRG Renew
CONSTRUCTION: Sunora Energy Solutions
DATE COMMISSIONED: February 2015
INSTALLATION TIME FRAME: 120 days
LOCATION: Las Vegas, NV, 36.1°N
SOLAR RESOURCE: 7.62 kWh/m2/day
ASHRAE DESIGN TEMPERATURES: 108°F 2% average high, 25°F extreme minimum
ARRAY CAPACITY: 6.354 MWdc
ANNUAL AC PRODUCTION: 10,379 MWh
MODULES: 3,780 Hanwha HSL 72 300, 300 W STC, +5/-0 W, 8.22 Imp, 36.5 Vmp, 8.72 Isc, 45.5 Voc; 13,320 Hanwha HSL 72 305, 305 W STC, +5/-0 W, 8.32 Imp, 36.7 Vmp, 8.8 Isc, 45.7 Voc; 4,296 JA Solar JAP6-72-285, 285 W STC, ±3%, 7.7 Imp, 37.01 Vmp, 8.38 Isc, 44.6 Voc
INVERTERS: 3-phase 480 Vac service, 203 SMA America Sunny Tripower 24000TL-US, 24 kW rated output, 1,000 Vdc maximum input, 450–800 Vdc MPPT range; 203 SMA America Connector Units combine strings at each inverter, 15 A fuses
ARRAY: Roof Areas 1–4, Hanwha modules, 18-module 1,000 Vdc nominal source circuits (for 305 W modules: 5,490 W, 8.32 Imp, 660.6 Vmp, 8.8 Isc, 822.6 Voc), six source circuits per inverter (32.94 kW, 49.92 Imp, 660.6 Vmp, 52.8 Isc, 822.6 Voc); Roof Areas 5–6, JA Solar modules, 12-module 600 Vdc nominal source circuits (3,420 W, 7.7 Imp, 444.12 Vmp, 8.38 Isc, 535.2 Voc), eight source circuits per inverter (27.36 kW, 61.6 Imp, 444.12 Vmp, 67.04 Isc, 535.2 Voc); 6.354 MWdc array total
ARRAY INSTALLATION: TPO roof membrane, Unirac Roof Mount (RM) system, ballast and hot-welded anchor system, 180° azimuth, 10° tilt, Eaton’s B-Line series dc cable management system
INVERTER AGGREGATION: 22 Eaton Pow-R-Line 3FQS 400 A panelboards, four Eaton 2,500 A Pow-R-Line switchboards, combined inverter output transformed to 12 kVac via roof-mounted Eaton’s Cooper Power series medium-voltage pad-mount transformers with switchgear located at ground level
SYSTEM MONITORING: Locus Energy