True South Solar: Buckhorn Springs Retreat Center
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The history of southern Oregon’s Buckhorn Springs dates back to the late 1800s when James Clarke Tolman built a resort to take advantage of the site’s mineral water and carbon dioxide springs, which many believed had curative properties. Buckhorn Springs’s current owners, Bruce and Leslie Sargent, purchased the run-down resort in 1987 and embarked on a life-long family effort to restore the historic structures and create a modern retreat center steeped in the site’s rich history. In the summer of 2015, True South Solar (TSS) added a modern event to the property’s historical time line—a 24 kW PV system.
The property’s sloping site was a good candidate for six pole-mounted arrays. The crew outlined property and creek setbacks and mocked up the pole-mount locations with paint to determine the optimal spacing between them. Although they staggered the poles down the hill in an organic manner, the installers made sure to line up each set of poles on the east-west axis to create a nice visual line between them.
TSS selected MT Solar’s Top of Pole Mounts for the project. The product includes a chain hoist and pulley system that allows workers to assemble the array at waist level and lift it into place, minimizing the need for ladders or heavy equipment. MT Solar’s pole mounts integrate with the installer’s preferred top-down rail system. TSS used SnapNrack rails for the project, in part due to the crew’s familiarity with installing this particular rail system.
This was the first time TSS had worked with MT Solar’s pole mounts, and a few unanticipated challenges came up. The system includes a hand crank that allows individuals to easily adjust the array’s tilt angle. However, the crank is on the backside of the pole where a combiner or disconnect is typically located. To avoid working clearance issues, installers may need to mount enclosures and associated circuits on the side of the pole when using the MT Solar mount. Another product-specific consideration is that since installers assemble the array at waist level before lifting it into place, they need to delay the installation of enclosures or conduits that fasten to the pole until they raise the array into its final position. TSS did not find this to be a big issue, but it did alter its standard pole-mount installation workflow.
The project uses three SunPower 7 kW non-isolated inverters with dual MPP trackers. Its physical and electrical layout worked out nicely, with a dedicated MPPT for each pole-mounted array. Each mount supports 12 SunPower modules configured in two six-module source circuits. TSS used MC4-Y connectors to parallel these circuits. Because the system uses non-isolated string inverters, Code requires both ungrounded power conductors to be de-energized when the circuit is opened. Using MC4-Y connectors to parallel two source circuits allowed TSS to use two-pole rather than four-pole disconnects, reducing both material and labor costs.
“The Buckhorn Springs project was our first experience with the MT Solar pole-mount system. Although we encountered a few unanticipated challenges, the added speed and safety of building arrays at waist level with two feet on the ground has sold us on this product.”
—Ry Heller, True South Solar
DESIGNER AND LEAD INSTALLER: Ry Heller, True South Solar, truesouthsolar.net
INSTALLATION CREW: Josh Neale, Colin Bashant, Mike Goglin and Oshia Golden
DATE COMMISSIONED: August 2015
INSTALLATION TIME FRAME: 6 days
LOCATION: Ashland, OR, 42.2°N
SOLAR RESOURCE: 4.9 kWh/m2/day
ASHRAE DESIGN TEMPERATURES: 96.8°F 2% avg. high, 17.6°F extreme min.
ARRAY CAPACITY: 23.54 kWdc
ANNUAL AC PRODUCTION: 32,020 kWh
MODULES: 72 SunPower SPR-E20-327, 327 W STC, +5/-0%, 5.98 Imp, 54.7 Vmp, 6.46 Isc, 64.9 Voc
INVERTERS: Single-phase 120/240 Vac service; three SunPower SMA America SB7000TL-US with Secure Power Supply, 7 kW rated output, 600 Vdc maximum input, 245–480 Vdc MPPT range, 125–500 Vdc operating voltage range, dual MPPT
ARRAY: Six modules per source circuit (1,962 W, 5.98 Imp, 328.2 Vmp, 6.46 Isc, 389.4 Voc); two source circuits per MPP tracker (3,924 W, 11.96 Imp, 328.2 Vmp, 12.92 Isc, 389.4 Voc); four source circuits per inverter (7,848 W, 23.92 Imp, 328.2 Vmp, 25.84 Isc, 389.4 Voc); three inverters total; 23.54 kW array total
ARRAY INSTALLATION: Ground mount, six MT Solar 8-inch Top of Pole Mount, 180° azimuth, fully adjustable array tilt from 0° to 90°
STRING INVERTER AGGREGATION: 125 A inverter combiner panel, 40 A two-pole breaker per inverter
SYSTEM MONITORING: SunPower monitoring system with smartphone app