Project Profiles

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Located at a residential horse farm, a solar shade structure was built to offset the electrical consumption for the service it is interconnected to while providing a location for outdoor recreation. Aesthetics were a primary consideration during the system’s design and installation.

Tropical storms regularly pass through Florida, and the array structure stands nearly 10 feet tall at its highest point, so careful consideration was required. The custom mounts, designed by ASE, use standard PV mounting rails to support the modules and transfer the load to the steel substructure. Trim pieces were added to conceal the modules’ wiring and provide a uniform appearance. The top and side trim pieces are perforated to provide sufficient airflow for cooling.

AAA Builders of Micanopy, Florida, completed the concrete and structural work. The design called for individual 32-inch–deep concrete pads under each leg section, along with a 3-inch slab under the entire array. Each leg is secured to two 12-inch J-bolts embedded into the pads. Dan House Electric was responsible for the system’s electrical work. The inverter is located outside on a pedestal mount, 75 feet from the array, to minimize the visual impact of the electrical equipment and to allow for a convenient location for the utility interconnection.

“The structural considerations for this array were difficult enough on their own. The unique aesthetic requirements made the Micanopy array one of the more rewarding residential installations we have done.”

Daniel House, President, Dan House Electric


DESIGNER: Chris Morrison, Planet Green Solutions,
LEAD INSTALLER: Daniel House, Dan House Electric,
LOCATION: Micanopy, FL, 29.8°N
SOLAR RESOURCE: 5.1 kWh/m2/day

Equipment Specifications

MODULES: 12 Canadian Solar CS6P-230P, 230 W STC, +2.2%/-0%, 7.78 Imp, 29.6 Vmp, 8.34 Isc, 36.8 Voc
INVERTER: Motech PVMate 2900U- 240, 2.9 kW, 600 Vdc maximum input, 200–550 Vdc MPPT range, 240 Vac output
ARRAY: One string of 12 modules (2,760 W, 7.78 Imp, 355.2 Vmp, 8.34 Isc, 441.6 Voc)
ARRAY INSTALLATION: ASE custom ground mount; 180° azimuth, 20° tilt (manually adjustable)

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In 2009, the budget advisory committee of the Portola Valley School District made a decision to have PV systems installed at the campuses of two schools in its district. Late that year, the school district received a federal stimulus award that helped fund the projects. In addition, the district was awarded two tax-credit bond allocations, making the district eligible for tax credits. Following an RFP release, Real Goods Solar (RGS) was contracted to install a 173 kW array at the district’s Corte Madera, California, campus and a 92 kW array at the Ormondale campus. The two arrays are expected to offset nearly 80% of the schools’ annual energy consumption.

The Corte Madera installation was spread across 10 buildings with arrays having different orientations and tilt angles. Due to the multiple roof orientations, RGS decided to utilize Enphase inverters. The microinverters allowed RGS to maximize the arrays’ power density on each roof and mitigate potential shading issues caused by trees surrounding the buildings.

The school district worked with CJW Architecture to establish a base design and develop the RFP for the Corte Madera project. The school was constructed under the oversight of the Division of State Architecture (DSA), which, among other tasks, develops structural safety requirements for K-12 schools. The DSA requirements precluded the use of S-5! or other nonpenetrating mounting methods for the galvanized steel roofs. In response, RGS used custom-built penetrating brackets to meet the DSA’s and structural engineer’s requirements.

To minimize new wire runs, RGS terminated each inverter ac branch circuit at the host building’s subpanel. This approach eliminated the need to bring all the individual branch circuits to an ac combiner panel located at the campus’s main service entrance. However, to comply with utility interconnection standards, a visible, lockable ac disconnect was required at the existing meter location. Because the utility would not accept remote disconnects at each array, RGS installed a new main service disconnect switch.

The installation at the Ormondale campus was much more straightforward. The project was also subject to DSA requirements, but the buildings’ tar-and-gravel roofs accommodated a more conventional racking system. Standard Unirac standoffs were used to secure the array racking to the buildings’ structural members. The roof surfaces at Ormondale are low slope and the modules are mounted at a 5° tilt angle to increase the array’s power density. The inverters’ proximity to the main service entrance allowed RGS to combine the individual ac branch circuits in a combiner panel and connect the output of that panel to the main service.

Each installation utilizes both Enphase Enlighten and Deck Monitoring systems. The Enphase platform allows the module-level monitoring desired by the school district. The Deck Monitoring platform meets the independent monitoring requirement of the CSI’s performance-based incentive program. Initially, the Envoy units in different buildings had issues communicating with inverters on separate roofs. Enphase technicians visited the site, and, through software and firmware updates, were successful in getting all the units to report properly.

“The unique structural requirements and multiple buildings necessitated complex design and installation solutions. We were very grateful to Enphase for the support they provided in troubleshooting the monitoring issues that we encountered. In the end, this turned into a superior installation that exceeded the client’s expectations.”

Stu Davis, project engineer, Real Goods Solar


DESIGN TEAM: Real Goods Solar,
LEAD INSTALLER: Troy Robinson, site superintendent, Real Goods Solar
LOCATION: Portola Valley, CA, 37°N
SOLAR RESOURCE: 4.9 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: Per Solar ABCs Solar Reference Map: 84°F/32°F

Equipment Specifications

MODULES: 1,127 Sharp NU-U235F4, 235 W STC, +10/-5%, 7.81 Imp, 30.1 Vmp, 8.5 Isc, 37.0 Voc
INVERTERS: 1,127 Enphase M215-60- 2LL, 215 W, 45 Vdc maximum input, 22–36 Vdc MPPT range, 3-phase, 208 Vac output
ARRAY: 25 inverters per branch circuit (typical)
ARRAY INSTALLATION: Corte Madera school: standing-seam metal roofs, custom penetrating module-mounting brackets, multiple azimuth and tilt values (10 buildings total with varied roof surface orientations and pitches); Ormondale school: tar-and-gravel roofs, Unirac standoffs and rails, 135° and 225° azimuths, 5° tilt
SYSTEM MONITORING: Enphase Envoy gateways and Enphase Enlighten software (module-level monitoring); Deck Monitoring (to meet California Solar Initiative performance-based incentive independent monitoring requirement for the aggregated systems)

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Bonnie Johnson and Paul Torrence represent ideal candidates for a residential grid-tied system. The retired couple has a goal of achieving net zero energy use and prior to the PV installation had invested in energy-efficient household appliances. The installed 6.58 kW array is sized to generate approximately 75% of their annual electricity. When a planned domestic solar water heating system is installed, their overall energy use will be close to net zero.

A DPW Solar Multi-Pole Mount system was specified to provide adequate ground clearance and to minimize the number of ground penetrations required, reducing installation time and cost compared to other ground-mount options that were considered. DPW Solar provided engineering assistance for the footing specifications and associated racking components. Dirt work was subbed out to a local skid steer operator with a 24-inch auger.

DPW Solar’s redesigned Multi-Pole Mounts, released in 2010, have improved setscrews in the rail-to-pipe brackets that strengthen the mounting system. The installed Sharp NU-235F3 modules feature two cross rails that add to the array’s overall rigidity and resistance to wind loading.

Wildfires are a real concern in this part of the country. To protect against this threat, the ground underneath the array was surfaced with weed barrier and crushed rock extending 4 feet beyond the southern edge.

“I’ve seen what a hot, fastburning grass fire can do to ground-mounted PV arrays that are installed without adequate ground clearance or surface preparation—it melts aluminum racking and modules wholesale. In our location, it’s worth it to take every reasonable precaution to minimize the risk of potential array damage due to wildfire.”

Eric Hansen, True South Solar


DESIGNER: Jacob Wood, design and sales manager, True South Solar,
LEAD INSTALLER: Eric Hansen, general manager, True South Solar
LOCATION: Williams, OR, 42°N
SOLAR RESOURCE: 4.5 kWh/m2/day

Equipment Specifications

MODULES: 28 Sharp NU-235F3, 235 W STC, +10%/–5%, 7.81 Imp, 30.1 Vmp, 8.5 Isc, 37.0 Voc
INVERTER: SMA SB 7000US, 7 kW, 600 Vdc maximum input, 250–480 Vdc MPPT range, 240 Vac output
ARRAY: 14 modules per source circuit (3,290 W, 7.81 Imp, 421.4 Vmp, 8.5 Isc, 518.0 Voc) with two circuits total (6,580 W, 15.62 Imp, 421.4 Vmp, 17.0 Isc, 518.0 Voc)
ARRAY INSTALLATION: DPW Solar Multi-Pole Mounts on 4-inch Schedule 40 pipe, 210° azimuth, 30° tilt
ARRAY COMBINER: OutBack FWPV-8, 15 A fuses


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Salt Lake County and Bella Energy recently commissioned a 1.652 MW rooftop PV system on the Calvin L. Rampton Salt Palace Convention Center in downtown Salt Lake City. The array is the largest roof-mounted system in the state of Utah and covers approximately 170,000 square feet of the convention center, offsetting 17% of the building’s annual energy consumption. The New Markets Tax Credit Program in part financed the project, which is one of a small number of PV projects financed using this mechanism. Bella Energy and CarbonFree Technology were joint developers, and Bella acted as the EPC contractor on the system. Bella Energy employed local contractors Clark’s Quality Roofing and Rydalch Electric to complete the physical installation.

Bella Energy initially proposed a 2 MW system. However, given uncertainty surrounding the financing mechanism, the developers decided to design and engineer the system in scalable sections prior to the financial closing, so that they could quickly scale it down should the available funding be reduced. To accommodate the final available project funding, they reduced the system to 1.652 MW by removing 348 kW of array capacity and the associated inverter and BOS requirements.

The large size of this PV system, coupled with a requirement to make a low-voltage interconnection, required two new electrical services for the building— and the initial plan connected those services to the inverters only. In an effort to have the building consume all of the generated energy instead of exporting it, the developers opted to connect the services to the existing utility transformers that historically experienced the largest loads. Rocky Mountain Power, the local electric utility, completed impact studies on the effects of interconnection and provided support during interconnection and protective relay programming.

One of the major challenges in implementing the system was the installation of attachments to the roof that the site’s seismic classification required. The need for more than 700 attachments created challenges for both design and implementation. Because the building had been designed to be built in multiple phases, careful consideration and verification was required to ensure that the attachments were positioned correctly over the building’s purlins based on the size and the wind loading imposed on each subarray. Installers used Unirac FastFoot assemblies for the attachments, which they assembled off-site and installed as weather allowed throughout the project’s winter installation time frame. After removing insulation, the installers secured wood blocking to the roof ’s metal deck to build up to membrane level, where they attached the FastFoot assemblies. They sealed each penetration with a hotair– welded TPO boot to satisfy the roof warranty holder’s requirements.

“One of the most arduous phases of the design was creating an accurate model of the building. The Salt Palace was constructed in several stages across decades. Creating a model of the 635,000-squarefoot rooftop required sifting through a plethora of architectural and structural drawings from several different plan sets, extracting relevant information, recreating and stitching together dozens of small sections into a single drawing, and then reconciling the result with actual on-site measurements and a professional survey of the roof. This up-front effort was crucial to ensuring the completeness and accuracy of the final layout and racking design.”

Leif Cook, Bella Energy



DESIGNER: Leif Cook, design engineer, Bella Energy,
INSTALLATION TEAM: Andy Blakeslee, site superintendent; Shannon Welch, construction project manager; Dana Mosman, operations manager, Bella Energy; Clark’s Quality Roofing, racking and module installation, Rydalch Electric, electrical installation,
LOCATION: Salt Lake City, UT, 40.8°N
SOLAR RESOURCE: 5.3 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 97°F/3°F

Equipment Specifications

MODULES: 6,006 Suntech STP275- 24/Vd, 275 W STC, +5/-0%, 7.84 Imp, 35.1 Vmp, 8.26 Isc, 44.7 Voc
INVERTERS: 3-phase, 480 Vac service; two Solectria SGI 500, 500 kW, 625 Vdc maximum input, 300–500 Vdc MPPT range; one Solectria SGI 300, 300 kW, 625 Vdc maximum input, 300–500 Vdc MPPT range
ARRAY: 11 modules per source circuit (3,025 W, 7.84 Imp, 386.1 Vmp, 8.26 Isc, 491.7 Voc); 15 source circuits per combiner, typical (45.4 kW, 117.6 Imp, 386.1 Vmp, 123.9 Isc, 491.7 Voc); 500 kW inverters with 210 source circuits per inverter (635.3 kW, 1,646 Imp, 386.1 Vmp, 1,735 Isc, 491.7 Voc); 300 kW inverter with 126 source circuits total (381.2 kW, 988 Imp, 386.1 Vmp, 1,041 Isc, 491.7 Voc)
ARRAY INSTALLATION: TPO roofing, Unirac ISYS Roof 1.5 racking, 180° azimuth, 10° tilt
ARRAY STRING COMBINERS: 37 SolarBOS Disconnect Combiners, 15 A fuses
SYSTEM MONITORING: Draker Sentalis 800 base station with zone monitoring, environmental sensors and Shark revenue-grade meters

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IRC Solar Roof Systems, an affiliate of IRC Industrial Roofing Companies, was contracted to develop a 186 kW PV installation at Belmont Hill School, a private school located in Belmont, Massachusetts. The 14,000-square-foot array is installed on the roof of the school’s Jordan Athletic Center and generates enough electricity to offset approximately 20% of the facility’s electrical demand.

The 778-module system is one of the largest school-based projects in eastern Massachusetts and the first commercial PV interconnection for the municipalowned local utility, Belmont Municipal Light Department (BMLD). An initial challenge was working with BMLD’s existing regulations for commercial solar production. While Massachusetts requires investor-owned utilities to support distributed generation and system net metering, municipal-owned utilities need participate only voluntarily. This required IRC to work with the BMLD board to gain approval of the project’s net metering program.

In the design phase, a single central inverter was considered. However, the only available location was not ideal because the inverter would have been located in a high-traffic area near the school’s delivery entrance. Multiple string inverters were the preferred solution based on an available exterior wall surface at the second-floor level. An adjacent low-slope roof provided the installation crew and future maintenance crews a safe and convenient working surface. School administrators also favored the location since the inverters are not visible from ground level.

The structure supporting the main standing-seam metal roof over the Jordan Athletic Center’s ice rink is composed of light-gauge purlins with 4.5-foot on-center spacing. Utilizing an attachment method such as the railless S-5! PV Kit would have streamlined the attachment to the metal roofing seams but would have resulted in excessive point loading between the structural purlin members. The engineered solution uses IronRidge XRS extruded aluminum rails in conjunction with S-5! mounting clamps to span the structural members while transferring the collateral loads created by the PV array directly to the purlins.

The PV source circuits are combined at the array to minimize the number of conductors from the roof to the inverter location. This design approach required 14 disconnecting combiners that are mounted on the roof surfaces in close proximity to the array. The location of the combiners assisted with PV source-circuit wire management by allowing an easy transition to conduit for the output circuits. The inverters’ 277 Vac circuits are combined in a panelboard at the inverter location to simplify the conductor run to the facility’s main distribution panel.

IRC worked with the school’s faculty and staff to integrate an educational component that allows students, teachers and parents to view real-time and historical performance and environmental data. A 40-inch flat-screen monitor installed in the athletic building displays continuously updated system information that highlights the environmental benefits of Belmont Hill School’s solar project. An online classroom supplements the on-site learning opportunities.

“Engineering a solution at Belmont Hill School was made easier by the partnership of the school, the local energy committee and the support of the Belmont Municipal Light Department. IRC Solar Roof Systems is contracted to provide ongoing O&M for both the PV and the metal roofing systems.”

Kurt Penney, business development, IRC Solar Roof Systems


DESIGNER: Steven J. Strong, president, Solar Design Associates,
LEAD INSTALLER: Michael Donnelly, director of electrical operations, IRC Solar Roof Systems,
DATE COMMISSIONED: January 16, 2012
LOCATION: Belmont, MA, 42.5°N
SOLAR RESOURCE: 4.3 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 90°F/1°F

Equipment Specifications

MODULES: 778 Sharp ND-240QCJ, 240 W STC, +5/-0%, 8.19 Imp, 29.3 Vmp, 8.75 Isc, 37.5 Voc
INVERTERS: 3-phase, 277/480 Vac service; 14 Fronius IG Plus V 12.0-3WYE277, 12 kW, 600 Vdc maximum input, 230–500 Vdc MPPT range
ARRAY: 14 modules per source circuit (3,360 W, 8.19 Imp, 410.2 Vmp, 8.75 Isc, 525 Voc); four source circuits per inverter typical (13.4 kW, 32.8 Imp, 410.2 Vmp, 35 Isc, 525 Voc); 186.7 array capacity total
ARRAY INSTALLATION: Roof-mount, steel standing-seam roofing panels, IronRidge XRS racking, S-5! mounting clamps, 210° azimuth, 18.4° tilt
ARRAY STRING COMBINERS: 14 Bentek six-pole Integrated Disconnect Combiners, 15 A fuses
SYSTEM MONITORING: DECK Monitoring production and environmental monitoring; Obvius AcquiSuite server, dashboard and Modbus communication

Primary Category: 

During our initial site visit to Charlene Summers’ residence, we discovered that the roof offered us a choice between installing either an east- or west-facing array. At the same time, the backyard seemed very sunny and the existing patio slab was still hot from the afternoon sun. Then the idea hit us—a PV patio cover. The patio cover would provide much-needed shade to enjoy the long summer afternoons, while simultaneously producing energy to offset the customer’s electric bill.

The challenges were building on top of the existing slab and meeting the client’s aesthetic concerns, particularly regarding the presentation of the bottom side of the modules. The first challenge was met by cutting out three 2-by-2- foot squares in the slab and digging the footings for three steel posts. Installing lattice between the rafters solved the aesthetic challenge by providing a visual screen underneath the array.

The rest of the structure was a standard wood frame, painted white. For a sleek look, the modules were mounted using the Unirac SunFrame shared rail system. Most of the labor went into installing the lattice on the underside of the structure after the PV system was installed.

“If I had that one to do over, I would install the lattice across the top of the rafters before installing the modules. That would have saved a ton of time.”

—Bret Alexander, Tahoe Solar Designs


DESIGNER: Leslie Ames, president, Tahoe Solar Designs,
LEAD INSTALLER: Bret Alexander, foreman, Tahoe Solar Designs
LOCATION: Minden, NV, 39°N
SOLAR RESOURCE: 5.46 kWh/m2/day

Equipment Specifications

MODULES: 20 Mitsubishi PVMF175UD4, 175 W STC, +10%/-5%, 7.32 Imp, 23.9 Vmp, 7.93 Isc, 30.2 Voc
INVERTER: SMA SB 3000US, 3 kW, 500 Vdc maximum input, 200–400 Vdc MPPT range
ARRAY: Ten modules per source circuit (1,750 W, 7.32 Imp, 239 Vmp, 7.93 Isc, 302 Voc) with two circuits total (3,500 W, 14.64 Imp, 239 Vmp, 15.86 Isc, 302 Voc)
ARRAY INSTALLATION: Custom wooden awning, Unirac SunFrame rail system, 195° azimuth, 10° tilt
ARRAY COMBINER: Inverter integrated with dc disconnect, no fusing required
SYSTEM MONITORING: Inverter display

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The Sacramento Municipal Utilities District (SMUD) Home of the Future, built by RJ Walter Homes in Folsom, California, is the first LEED Platinum house built in the Sacramento region and is only the second LEED Platinum home built in Northern California. The award winning design was created by a consortium of partners including SMUD, the US Department of Energy’s Building America program, Building Science Corporation and the National Renewable Energy Laboratory.

The SMUD Home of the Future combines beauty, affordability and comfort while leading the way to an environmentally sustainable future. Special care was taken in selecting the materials and components of the house to make the lowest possible environmental impact while providing the highest energy performance and best indoor air quality. The goal of SMUD’s program is to design and build true zero energy homes— homes that produce as much energy as they use.

OCR Solar & Roofing provided the design, installation and commissioning of the PV system with battery backup and worked with SMUD, BP Solar and NREL on the installation of the advanced PV system monitoring package. In addition to the PV system, the house also has a solar assisted domestic hot water and heating system.

"Compared to homes built to California’s already stringent Title 24 energy standards, the SMUD Home of the Future not only reduces annual energy use and utility bills by 80%, including net zero electric use, but it also cuts peak demand by 80%."

Bill Reaugh, OCR Solar & Roofing


DESIGNER: Bill Reaugh, technical services manager, OCR Solar & Roofing,
PROJECT MANAGER: Fred Dever, solar general superintendent, OCR Solar & Roofing
DATE COMMISSIONED: September 2008 Installation timeframe: 120 days (over the course of new construction)
LOCATION: Folsom, CA, 38.7°N
SOLAR RESOURCE: 5.32 kWh/m2/day

Equipment Specifications

MODULES: 27 BP Solar BP 175I, 175 W STC, +5%/-5%, 4.9 Imp, 35.8 Vmp, 5.5 Isc, 43.6 Voc
INVERTER: Xantrex XW 6048, 6 kW
CHARGE CONTROLLERS: Two XW SCC, 150 Vdc maximum input, 60 A MPPT charger
BATTERIES: 12 Dekka 8G31, 12 Vdc, 98 Ah, wired for 294 Ah at 48 Vdc
ARRAY: Three modules per string (525 W, 4.9 Imp, 107.4 Vmp, 5.5 Isc, 130.8 Voc), four and five circuits per charge controller (2,100/2,625 W, 19.6/24.5 Imp, 107.4 Vmp, 22.0/27.5 Isc, 130.8 Voc)
ARRAY COMBINER: Two Midnight Solar MNPV6 with 10 A, 150 Vdc breakers
SYSTEM MONITORING: SMUD bidirectional kWh meter on inverter output circuit and NREL sponsored monitoring system with weather station
ARRAY INSTALLATION: Roof mount on composition shingles, low profile BP Solar Integra racking, 160° azimuth, 23° tilt

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LPS Industries, a flexible packaging manufacturer in Moonachie, New Jersey, selected Solis Partners to install what was the largest Solyndra thin-film PV array in the US at the time of commissioning. A new white TPO roof, an integral part of the cylindrical CIGS PV system, was installed just prior to the array to enhance the reflected light available to the panels.

Initially, the roof was capable of accommodating less than 2 additional pounds per square foot of distributed loads. To help overcome this, Solis reinforced the main roofing beams to support up to 4 pounds per square foot. Solyndra panels proved to be the best match for the roof as the total system added approximately 3 pounds per square foot on a distributed basis.

Solyndra provides a racking system specifically designed for its panels that utilizes cable trays to help facilitate proper wire management. In addition, the Solyndra panels include both male and female positive and negative output conductors on each panel. Solis took advantage of the low current output in relation to the maximum series fuse rating and placed as many as three strings in parallel before connecting to a combiner box. This reduced the overall number of source circuits and associated wiring and overcurrent protection devices.

“Because the LPS facility is located in a high-wind zone rated at 110 mph, a flat-panel PV system would have required significant ballast or roof penetrations that would have been unfeasible or cost prohibitive. The Solyndra system required only minimal structural reinforcement and allowed us to move forward with the project without impacting the integrity of the building or day-to-day operations at LPS.”

Rick Surgent, Solis Partners


DESIGNER: Nickolai Cowell, design lead, Solis Partners,
LEAD INSTALLER: Rick Surgent, senior project manager, Solis Partners
LOCATION: Moonachie, NJ, 40.8°N

Equipment Specifications

PANELS: 3,870 Solyndra SL-001-182, 182 W STC, +4%/-4%, 2.46 Imp, 73.9 Vmp, 2.76 Isc, 96.7 Voc
INVERTERS: 3-phase, 480 Vac service, two PV Powered PVP260KW-LV, 260 kW each, 600 Vdc maximum input, 265–500 Vdc MPPT range
ARRAY: Five panels per source circuit (910 W, 2.46 Imp, 369.5 Vmp, 2.76 Isc, 483.5 Voc), typical combiner box input circuit consists of three paralleled source circuits (2,730 W, 7.38 Imp, 369.5 Vmp, 8.28 Isc, 483.5 Voc); 387 total source circuits per inverter (352.17 kW, 952 Imp, 369.5 Vmp, 1,068 Isc, 483.5 Voc); PV output circuits are connected to one 225 A and five 300 A fuses in the inverter’s integrated subcombiner
ARRAY COMBINER: 12 custom SolarBOS 24-input disconnecting combiners, 15 A fuses
ARRAY INSTALLATION: Solyndra mounts on a white TPO membrane, 218° azimuth, 0° tilt
SYSTEM MONITORING: Energy Recommerce REC Track 3

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SPG Solar was selected from an RFP process to design, engineer and install a single-axis tracking groundmount system for the Mammoth Community Water District. The 1 MW system is located at the Mammoth Lakes wastewater treatment plant and was financed through municipal bonds. Mammoth Lakes is a mountain community in California at an elevation of 7,880 feet above sea level, in a region that receives high winds, significant one-time snow events and an average yearly snowfall of 211.2 inches. Combined, these site characteristics presented some unique system design challenges.

SPG Solar’s engineering team designed an elevated PV array tracking system with support piles that extend 9 feet above grade to mitigate the impact of snow accumulation under the trackers. The array height provides ample clearance for the tracker to cycle 90° daily, from 45° east in the morning to 45° west in the evening. However, the elevated tracking system significantly increased the wind load on the array.

The tracker support’s pile foundation design required heavily reinforced 18-inch-diameter concrete columns that were set almost 9 feet deep. The reinforced columns rise 3 feet above the finished grade elevation for additional pile support. Geotechnical testing that was performed during the design phase of the project indicated that most of the site subterrain is rock. In addition to the large piles, 6-inchthick equipment pads with added spread-footings were needed to support the inverters and transformers.

The two 500 kW SMA Sunny Central inverters are power limited to 499 kW for rebate purposes. The arrays connected to each inverter are installed with different azimuth angles to conform to the site’s geometry. For each array, there are two drivelines. Each driveline’s motor utilizes a controller that identifies its location with a realtime GPS system. The GPS calculates the sun’s location throughout the year to position the PV modules for maximum harvest. The controller’s algorithm uses a high-precision inclinometer to position the tracker.

To compensate for the movement of each array over the course of a day, the conductors from each source circuit come off of the array wings through a liquid-tight cord grip into a raceway. The combiner boxes are mounted adjacent to the raceway, with the source circuits fed to them through flexible conduits. The combined circuits are then sent underground and routed to the inverter pads. The ac power from the two inverters is stepped up through a pair of 500 kVA 480:208Y/120 Vac transformers and delivered to a power panelboard that has two 800 A breakers for the inverters and two 40 A breakers for tracker motors and controls. The power output is then transmitted to the main 1,600 A PV disconnect, which couples to the line side of the facility’s existing 480 Vac switchgear.

“The project’s location presented the greatest challenges to our team. All of the site conditions—wind, snow and rocky terrain—added their own layer of complexity. We took on the challenge and engineered an innovative solution, maximizing solar production.

—Doug Haigh, SPG Solar


DESIGNER: Doug Haigh, senior designer, SPG Solar,
LOCATION: Mammoth Lakes, CA, 37.4°N
SOLAR RESOURCE: 6.5 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 100°F/-9°F

Equipment Specifications

MODULES: 4,407 Astronergy CHSM 6610M, 230 W STC, +5/-0 W, 7.93 Imp, 29.03 Vmp, 8.52 Isc, 37.48 Voc
INVERTERS: 3-phase, 480 Vac service; two SMA Sunny Central 500HE-US, 500 kW, 600 Vdc maximum input, 330–600 Vdc MPPT range
TRACKERS: four SPG Solar Sunseeker single-axis trackers, +45° to -45° tracking range
ARRAY: 13 modules per source circuit (2,990 W, 7.93 Imp, 377.4 Vmp, 8.52 Isc, 487.2 Voc); 26 source circuits per combiner typical (77.7 kW, 206.2 Imp, 377.4 Vmp, 221.5 Isc, 487.2 Voc); Inverter 1: 183 source circuits total (547.2 kW, 1,451 Imp, 377.4 Vmp, 1,559 Isc, 487.2 Voc); Inverter 2: 156 source circuits total (466.4 kW, 1,237 Imp, 377.4 Vmp, 1,329 Isc, 487.2 Voc)
ARRAY INSTALLATION: tracked ground mount, 180° and 204° azimuths, three module strings per wing (half-row) installed on each side of tracker’s drive line
ARRAY STRING COMBINERS: 13 Bentek Integrated Disconnect Combiners, 15 A fuses
SYSTEM MONITORING: proprietary SMA America monitoring with integrated ERI (Power-One) datalogger, 24/7 video surveillance

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The Checco home is located in the Clifton neighborhood of Cincinnati, a historic area of Victorian-era homes. This home, however, did not lend itself to optimal solar mounting due to its small roof size and significant shading from mature trees. The owner constructed a backyard garage on the north end of the lot with a solar array in mind. The garage also serves as an artists’ studio for the homeowners.

The design process started with a review of the customer’s historic energy usage, which was adjusted for recommended energy efficiency measures. Third Sun then collaborated with the customer’s architect to determine an appropriate roof orientation, size and pitch for the garage. The locations of the modules, inverter and BOS were carefully planned with future expansion in mind. There is room on the roof to double the array capacity, as well as enough wall space in the garage to add a second inverter at a later date.

Taking advantage of a state grant program of $3.50/watt reduced the gross cost of the system. The federal tax credit for residential installations also applied, resulting in a net cost for the customer that is competitive with existing utility rates. "This installation is straightforward on the surface: new-build, residential construction, asphalt shingle roof. But a great deal of careful planning was required, involving multiple parties: owner, architect and GC. The reason this project works - and works well for our customer - is because a significant design investment was made at the beginning."

Randy Hatch, Third Sun Solar and Wind Power


DESIGNER: Randy Hatch, director of engineering, Third Sun Solar and Wind Power,
LEAD INSTALLER: Tim McMillian, field manager, Third Sun Solar and Wind Power
LOCATION: Cincinnati, OH, 39º N
SOLAR RESCOURCE: 4.5 kWh/m2/day

Equipment Specifications

MODULES: 24 SunPower SPR 225 BLK, 225 W STC, +5%/-5%, 5.49 Imp, 41.0 Vmp, 5.87 Isc, 48.5 Voc
INVERTER: SunPower SPR 5000m, 5 kW, 600 Vdc maximum input, 250–480 Vdc MPPT range
ARRAY: Eight modules per series string (1,800 W STC, 5.49 Imp, 328 Vmp, 5.87 Isc, 388 Voc) with three paralleled strings (5,400 W STC, 16.47 Imp, 328 Vmp, 17.61 Isc, 388 Voc)
ARRAY INSTALLATION: Roof mount on composition shingle, SunPower SmartMount racking, 180º azimuth, 30º tilt
ARRAY COMBINER: Inverter integrated, 15 A fuses
SYSTEM MONITORING: Inverterbased kWh meter


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