Project Profiles

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Oasis Montana and Simple Power teamed up to design and install a 50 kW PV system for the US Forest Service’s Missoula Technical Development Center (MTDC). This system is currently the largest PV installation in Montana. Funding for the project came from federal stimulus funds and a grant from North- Western Energy. To support the local economy and to comply with the Buy American Act, all employees and contractors were from the Missoula area, and American-made components were used.

The 223-module ground-mounted array utilizes a Unirac U-LA rack system configured to mitigate the impacts of heavy snowfall and shading from the perimeter fencing. To minimize excavation where existing underground utilities are located, a specially designed floating footer system is used for the racks’ foundation. In addition, a 20-module pole-mounted system is installed at the facility’s Visitor Center.

As with all federal buildings, security is of prime importance. Regulations prevent a direct external link to the Internet for a conventional web-based monitoring platform. The MTDC’s technology guru, Ted Etter, worked with Square D to customize one of the facility’s load analyzers to incorporate PV system monitoring. Centric Design developed a custom software solution to display system data on a 42-inch flat screen monitor used as an interpretive display in the Visitor Center’s lobby.

“Due to design constraints, such as array location, racking configuration and sourcecircuit string sizes, we determined that specifying multiple, low-power inverters allowed for increased granularity in the design to better suit the site’s parameters.”

Mark Dickson, Oasis Montana and Simple Power


DESIGNER AND LEAD INSTALLER: Mark Dickson, Oasis Montana,, and Simple Power,
LOCATION: Missoula, MT, 46.9°N
SOLAR RESOURCE: 4.4 kWh/m2/day

Equipment Specifications

MODULES: 243 Schott Poly 220, 220 W STC, +2%/-0%, 7.41 Imp, 29.7 Vmp, 8.15 Isc, 36.5 Voc
INVERTERS: 3-phase, 480 Vac service; two Solectria PVI 15KW, 475 Vdc maximum input, 205–380 Vdc MPPT range; two PVI 3000, single-phase, 240 Vac output, 600 Vdc maximum input, 200–550 Vdc MPPT range
ARRAY, INVERTERS 1 and 2: Ten modules per source circuit (2,200 W, 7.41 Imp, 297.0 Vmp, 8.15 Isc, 365.0 Voc) with eight circuits per inverter (17.6 kW, 59.28 Imp, 297.0 Vmp, 65.20 Isc, 365.0 Voc)
ARRAY, INVERTER 3: Nine modules per source circuit (1,980 W, 7.41 Imp, 267.3 Vmp, 8.15 Isc, 328.5 Voc) with seven circuits total (13.86 kW, 51.87 Imp, 267.3 Vmp, 57.05 Isc, 328.5 Voc)
ARRAY, INVERTERS 4 and 5: Ten modules per source circuit with one circuit per inverter
ARRAY INSTALLATION: Unirac U-LA ground mount, 180° azimuth, 30° tilt; two DPW Solar TPM10-SCT220 top-of-pole mounts, 180° azimuth, adjustable tilt
ARRAY COMBINERS: Three Blue Oak PV Products HCB8F, 15 A fuses; one OutBack FWPV12, 15 A fuses

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Reclamation District 108 (RD 108) procured this project to power its irrigation pumps at Sycamore Slough, 5.5 miles northwest of Knights Landing in Yolo County, California. The location and its associated environmental limitations, along with avoided-cost considerations, substantially challenged the project’s designers. The array is installed on productive farmland, so a high-power– density solution was needed to maximize energy production while minimizing valuable land area dedicated to the PV system. The project could not disturb an endangered garter snake habitat. In addition, it required elevation above the Sacramento River’s 100-year floodplain. Finally, it prescribed adherence to a narrow installation timeline of 60 days to avoid liquidated damages.

These very specific design parameters led RD 108 to select 30 Meca Solar dual-axis trackers, making this the first US installation to utilize the equipment. Meca Solar tracking systems have been installed throughout Spain in solar farms as large as 50 MW, with a current installed capacity of 180 MW worldwide since 2004.

Optimizing performance at the power-conditioning level was paramount. With a CEC-weighted efficiency of 97.5%, the transformerless, bipolar topology of the specified Advanced Energy Solaron inverter resulted in smaller-gauge dc wire runs and increased output compared to transformer-based central inverters.

To tackle the floodplain issue, the tracker foundations are elevated on a 3-foot earth berm. A reinforced concrete column provides an additional 4 feet on top of the manufacturer-recommended 2-foot foundation. This places the modules above the floodplain when in a stowed, horizontal position. Normally, the trackers are installed with three attached string inverters; however, a centralized approach is used here to flood potential. The inverter is placed on a custom-made steel platform, 16 feet above ground elevation and out of harm’s way. The 3-phase, 480 Vac output is transmitted to the service entrance located in a pump house via an aboveground pole line.

Complicating schedule efficiency, the trackers shipped from Spain, and the Trina modules came from China. Once the equipment arrived, the project was fast-tracked and completed in 45 days, ahead of schedule. It achieved its maximum rated capacity immediately. Through a net metering connection to the Pacific Gas and Electric Company grid, the array generates approximately 80%–90% of the pumping load, which varies with changing crop and weather patterns.

“For most of 28 days, I checked the weather data for the North Atlantic daily. I was tracking the delivery ship’s route relative to hurricanes roaring through the region, sweating the loss of even one day. It was a relief when the ship carrying the trackers arrived on schedule in Oakland, California. I am exceptionally proud of everyone on the team. We met our schedule and performance goals and turned over a beautifully constructed project that is a real showcase for the Meca tracker and a valuable asset to RD 108. The RD 108 staff, led by Manager Lewis Bair, were very supportive and helpful team players.”

Bob Parkins, Solar Development


DESIGNER: Bob Parkins, PE, director of engineering, Solar Development,, and Bob Parkins Consultants,
INSTALLATION TEAM: integration: Solar Development; electrical: Butterfield Electric,; structural: Ascent Builders,
LOCATION: Knights Landing, CA, 39°N
SOLAR RESOURCE: 5.5 kWh/m2/day

Equipment Specifications

MODULES: 1,680 Trina TSM-PC05, 230 W STC, +3%/-3%, 7.72 Imp, 29.8 Vmp, 8.26 Isc, 37.0 Voc
INVERTER: 3-phase, 480 Vac service, Advanced Energy Solaron 333 kW, 600 Vdc maximum input, bipolar ±330 to ±600 Vdc MPPT range, 97.5% CEC efficiency
TRACKERS: 30 Meca Solar MS Tracker 10+, dual axis, 1/3–1 HP 480 Vac 3-phase motors on both axes, 100 kWh annual motor consumption, gear motor and cogged crown wheel azimuth drive, electrically driven mechanical jack tilt drive
ARRAY: 56 modules per tracker, 14 modules per series string (3.22 kW STC, 7.72 Imp, ±417.2 Vmp, 8.26 Isc, ±518 Voc) 120 strings total—60 positive and 60 negative-to-ground (386.4 kW STC, 463.2 Imp, ±417.2 Vmp, 495.6 Isc, ±518 Voc)
ARRAY INSTALLATION: Customballasted surface foundations with embedded J-bolts for direct attachment to tracker framing
ARRAY COMBINERS: 16 Blue Oak HCB8F, NEMA 4X, fiberglass, 14 A fuses, eight PV source circuits per shared combiner (25.76 kW STC, 61.76 Imp, ±417.2 Vmp, 66.08 Isc, ±518.0 Voc); two trackers have individual combiners with four PV source circuits each (12.88 kW STC, 30.88 Imp, ±417.2 Vmp, 33.04 Isc, ±518.0 Voc)
DC DISCONNECTS: Six Square D H363RB 100 A, 600 Vdc heavyduty safety switches
SYSTEM MONITORING: Draker Laboratories Sentalis 1000, including string-level monitoring and Web-based reporting in accordance with CEC SB-1 performance requirements

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The solar thermal system integrates seamlessly with the 2,500-squarefoot home’s radiant heating system. Utilizing the STSS proprietary submerged coil design, the 415-gallon tank serves as the main heat source for space heating and as a preheat source for domestic hot water. A high-efficiency boiler serves as backup for the solar water heating system. In any space heating installation, introducing new controls is one of the biggest design challenges. Therefore, Alternative Power Solutions (APS) selected the STSS Energy Management Control (EMC) as the multisystem interface. The EMC wires directly to the boiler system controls and measures solar storage-tank temperature compared to thermostat set point, automatically switching to the boiler when the tank is unable to maintain the desired room temperature.

APS worked closely with the homeowners to orient the garage to true south and allocate the necessary rooftop collector area. SunMaxx racking eliminated the need for a custom-mount system, reducing material costs and installation time. The six SunMaxx collectors are mounted at a 65° tilt to optimize energy production in the winter heating months. If surplus heat is gained, a diverting valve directs fluid through a 150 K/Btu heat dump before returning it to the tank. An inline 500-gallon hot tub absorbs any additional heat produced in the summer, nearly eliminating the need for the heat dump. To maximize the R-value and avoid groundwater damage along the 70-foot underground pipe run from the array to the storage tank, the 1-inch Type K copper pipe was insulated with HT/Armaflex and sleeved in corrugated plastic tubing.

“The challenge of solar thermal is one of the main reasons we do it. The overall outcome here was fantastic. There is nothing more rewarding than helping someone reduce heating bills with the sun. With the new technology, solar thermal has caught right up to PV panels in life expectancy and system longevity.”

— Owen Pugh, Alternative Power Solutions


DESIGNER: Timothy Pugh, senior design engineer, Alternative Power Solutions,
LEAD INSTALLER: Owen Pugh, president, Alternative Power Solutions
LOCATION: Clayton, NY, 44°N
SOLAR RESOURCE: 4.2 kWh/m2/day
COLLECTOR ARRAY AREA: 332 square feet

Equipment Specifications

COLLECTORS: Six Silicon Solar Sun- Maxx SM-30 evacuated tube
HEAT EXCHANGERS: One 0.75-in.- by-120-ft. copper coil for solar input, one 0.75-in.-by-120-ft. copper coil for domestic hot water, two 0.75-in.-by- 120-ft. copper coils for space heating; all exchangers manufactured by STSS
PUMP: Grundfos UP26-99BF STORAGE: STSS 415-gallon tank with multiple submerged coils
CONTROLS: Caleffi iSolar-3 differential controller, STSS Energy Management Control
FREEZE CONTROL: Closed loop, propylene glycol
COLLECTOR INSTALLATION: Pitched roof, composition roofing material, SunMaxx racking system, 196° azimuth, 65° tilt

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The 1.1 MW Darden restaurant headquarters system is currently the largest privately owned PV installation in Florida. The array is composed of a custom galvanized steel solar canopy mounted over an existing parking garage, and a ballasted roof-mounted system installed on the Darden restaurant support center building. Combined, a total of 4,404 SolarWorld 250 W modules are deployed across these two arrays. Several factors played a role in making this a complex project from the conceptual design phase through system commissioning.

The most unique feature is the solar canopy structure that was built on top of the four-story, 85,000-squarefoot parking garage, which is located in Florida’s 120-mph wind zone. This canopy structure also supports vertically mounted solar modules in landscape format on the east-, south- and westfacing portions of the structure. These vertically mounted modules serve as an architectural facade that shields the canopy’s supporting galvanized steel trusses and girders when Darden’s employees and campus visitors view the structure from ground level.

Optimizing the rooftop PV system’s power performance ratio while keeping the total roof dead load below 5.5 pounds per square foot, and keeping a roof membrane penetration-free in a high wind zone was a complex challenge to manage. Various racking solutions were considered, but ultimately DPW Solar’s POWER-FAB CRS solution was selected. The CRS racking system secured the solar modules at an optimal 15° tilt angle. The array was laid out parallel to the building’s south edge, which has an azimuth of 147°. This approach allowed for a greater module-to-roof density ratio and provided an aesthetically pleasing installation while optimizing the system’s annual performance.

“During the installation of the roofmounted system, we encountered significant inconsistencies with the flatness of the roof surface, primarily at areas adjacent to roof drains. Our installation team worked with the racking manufacturer, DPW Solar, to quickly create a solution, which was to relocate the modules from the affected areas to alternate roof locations. The balance of the modules located on less severe slopes was accommodated with custom-designed EPDM-protected bases.”

Andreas Zahariadis, Kenyon Energy

“As is fairly common in the industry, for our client to qualify for the Federal ITC grant, we were tasked with getting the project designed, installed and commissioned by December 31, 2011. We made the commitment to our client to meet this critical deadline, and with the dedication and hard work of the entire project team, we completed installation of the 1.1 MW project on December 22—in 90 days!”

Tim Bonczek, senior VP of construction, Kenyon Energy


EPC CONTRACTOR: Andreas Zahariadis, VP of construction, Kenyon Energy,
ELECTRICAL CONTRACTOR: Tri-City Electrical Contractors,
DATE COMMISSIONED: December 22, 2011
LOCATION: Orlando, FL, 28.5°N
SOLAR RESOURCE: 4.4 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 93°F/30°F ARRAY CAPACITY: 1.1 MW

Equipment Specifications

MODULES: 4,404 SolarWorld Sunmodule SW 250 mono, Version 2.0 frame, 250 W STC, +5/-0 W, 8.05 Imp, 31.1 Vmp, 8.28 Isc, 37.8 Voc
INVERTERS: 3-phase, 480 Vac service, four Advanced Energy PVP260kW, 260 kW, 600 Vdc maximum input, 295–595 Vdc MPPT range, 3-phase, 480Y Vac output; six SMA Sunny Boy 5000- US, 5 kW, 600 Vdc maximum input, 250–480 Vdc MPPT range, singlephase, 277 Vac output
CANOPY ARRAY: 3,192 modules, three PVP260kW inverters, 14 modules per source circuit (3,500 W, 8.05 Imp, 435.4 Vmp, 8.28 Isc, 529.2 Voc); inverters 1 and 2: 78 source circuits each (273 kW, 627.9 Imp, 435.4 Vmp, 645.8 Isc, 529.2 Voc); inverter 3: 72 source circuits (252 kW, 579.6 Imp, 435.4 Vmp, 596.2 Isc, 529.2 Voc); 798 kW array total
CANOPY ARRAY INSTALLATION: Custom galvanized steel truss and girder mounting structure, 180° azimuth, 10° tilt
ROOFTOP ARRAY: 1,078 modules, one PVP260kW inverter, 14 modules per source circuit (3,500 W, 8.05 Imp, 435.4 Vmp, 8.28 Isc, 529.2 Voc); inverter 4: 77 source circuits (269.5 kW, 619.9 Imp, 435.4 Vmp, 637.6 Isc, 529.2 Voc); 269.5 kW array total
ROOFTOP ARRAY INSTALLATION: TPO roofing, ballast-only DPW Solar POWER-FAB CRS racking, 147° azimuth, 15° tilt
VERTICAL ARRAY: 134 modules, six SMA Sunny Boy 5000-US inverters, 10–13 modules per source circuit, two source circuits per inverter, 33.5 kW array total
VERTICAL ARRAY INSTALLATION: Unirac SunFrame racking mounted to custom steel canopy structure, 40 modules with 90° azimuth, 52 modules with 180° azimuth, 42 modules with 270° azimuth; 90° tilt
ARRAY COMBINERS: SolarBOS Disconnect Combiners, 15 A fuses
SYSTEM MONITORING: DECK Monitoring tracks inverter-direct output data and provides revenue-grade production metering for each 260 kW inverter and the electrical combination panel of the six 5 kW SMA inverters. Environmental monitoring includes ambient temperature, cell temperature, irradiance, humidity, barometric pressure, and wind speed and direction

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To provide students with the opportunity to compare technologies and relative system performance, Okanagan College’s solar water-heating system utilizes both flat-plate and evacuated-tube collector technologies. The hot water generated is used for domestic water and space heating. At the time of publication, Swiss Solar Tech had installed and commissioned Phase One of the system, composed of 18 flat-plate collectors. Phase Two will include the addition of eleven 30-tube evacuatedtube collectors. A direct digital control system transfers data such as collector temperatures, storage tank input and output temperatures, and energy production to a website for performance evaluation.

Swiss Solar Tech installed the collectors on custom-engineered racking. Unlike the PV arrays, the thermal collectors were installed at a more traditional 45° tilt angle to maximize energy production during the seasons of highest hotwater demand. Roof curbs were specified by the engineers and incorporated into the building and racking design. Because the system’s storage tanks are located in the building’s central mechanical room, the pipe run between the collectors and the tanks needed to be 148 feet. To minimize heating losses, this design required special consideration during the thermal system installation.

“Given that the PV and thermal systems were included in the original building design and all the various trades worked together, our installation was fairly smooth. The biggest challenge was coordinating all the aspects of construction to meet the federal government’s deadline for the incentives.”

—Tim Schulhauser, P. Eng., SkyFire Energy

Thermal Overview

DESIGNER: Roger Huber, CEO, Swiss Solar Tech,
LEAD INSTALLER: Richard Steuble, Swiss Solar Tech
COLLECTOR ARRAY AREA: 450 sq. ft. (flat-plate collectors), 512 sq. ft. (evacuated-tube collectors, gross area)

Thermal Equipment Specifications

COLLECTORS: 18 Viessmann Vitosol 200-F flat-plate, 11 Viessmann Vitosol 200-T evacuated-tube
HEAT EXCHANGERS: Two Advanced Industrial Components (AIC) LB3120DW
PUMPS: Grundfos UPS26-150
STORAGE: Eight Bradford White 120-gallon tanks
FREEZE CONTROL: Closed-loop glycol
COLLECTOR INSTALLATION: Lowslope roof, single-ply membrane, custom collector array mounts, 180° azimuth, 45° tilt
SYSTEM MONITORING: Direct digital control (DDC) with web-based data transfer

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Acting as guides to their community, the Boulder Valley Christian Church leaders place a strong emphasis on environmental stewardship. As a reflection of this commitment, they contracted Independent Power Systems (IPS) to install a turnkey PV system that would both promote the Church’s stewardship commitment and reduce its operating expenses.

Because the public utility, Xcel Energy, limited the system capacity eligible for the Colorado incentive program, IPS’s final design needed to maximize energy production. The Church’s roof was initially proposed for the array location. However, after modeling various array configuration scenarios, IPS designers determined that the roof ’s low angle, combined with sections that faced southwest and southeast, would not allow for the desired energy yield. A ground-mounted array located adjacent to the Church’s community garden was proposed as an alternative. This would increase installation costs per kW but result in an estimated 20% increase in annual energy production that would more than offset the upfront costs.

IPS researched several ground-mount racking systems to compare material and installation costs. The specified product needed to be robust enough to meet the site’s 120-mph wind-load and 30-psf snowload requirements. The Conergy Solar- Linea D driven-pile solution was selected for the project. The dual-post mounting system offered reduced pile-driving time and was less expensive in material and labor costs compared to other products that IPS evaluated because it required only a 4-foot pile ground-penetration depth. Each racking section was configured to support 26 modules, resulting in a streamlined aggregation of 13-module source circuits. This design facilitated the use of a single 36-circuit combiner box and one circuit to the inverter, lowering BOS costs.

“Pile location was critical for the racking system. If a pile contacted an obstruction before the refusal point, or the angle was out of tolerance, the options would have been limited. Fortunately, we did not hit anything serious and our posts went in the ground as planned.”

Simon Wood, Independent Power Systems


DESIGNERS: George Vaughan, project engineer; Simon Wood, project manager; Independent Power Systems,
LEAD INSTALLER: Jonah Coles, installation manager, Independent Power Systems
LOCATION: Boulder, CO, 40.0°N
SOLAR RESOURCE: 5.6 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 93°F/-13°F

Equipment Specifications

MODULES: 468 SunPower SER-235P, 235 W STC, +5/-3%, 7.91 Imp, 29.7 Vmp, 8.45 Isc, 36.8 Voc
INVERTER: 3-phase, 480 Vac service, Satcon PVS-100-UL, 100 kW, 600 Vdc maximum input voltage, 315–600 Vdc input voltage range
ARRAY: 13 modules per string (3,055 W, 7.91 Imp, 386.1 Vmp, 8.45 Isc, 478.4 Voc); 36 source circuits terminated in single combiner box (109.98 kW, 284.8 Imp, 386.1 Vmp, 304.2 Isc, 478.4 Voc)
ARRAY INSTALLATION: Conergy SolarLinea D ground mount, 180° azimuth, 40° tilt
ARRAY STRING COMBINER: Sun- Power 36-string combiner, 15 A fuses
SYSTEM MONITORING: SunPower SMS 2.0 web-based commercial monitoring

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LoyaltyOne, owner and operator of the AIR MILES Reward Program, engaged RESCo Energy to design and build a solar system on a call center facility that was already under construction. The building’s core and shell were designed to LEED Silver requirements, and the interior was designed to LEED Gold standards. LoyaltyOne decided to add a PV array eligible for feed-in tariff (FIT) rates through the Ontario Power Authority. Connection to the grid and receipt of a FIT contract occurred in early 2010. This was the largest PV array in Ontario’s FIT program at the time of commissioning. RESCo provided all design, permitting, project management, installation and commissioning services for the system.

When LoyaltyOne approached RESCo, no one in Canada had taken on a project of this scale. The Electrical Safety Authority (ESA) was just beginning to learn about large grid-connected PV arrays. RESCo worked collaboratively with the ESA and utility officials on the specifics of the project through a series of meetings. These meetings served to help the project as well as increase the knowledge about solar within Ontario. RESCo worked collaboratively with the entire team, including all subcontractors, to ensure that the project was completed on schedule, on budget and at a high level of quality. 

The array employs two solar technologies combined to provide both solar electric and solar heat to the building. In addition to the PV array, four 4 x 10 solar thermal collectors deliver approximately 34% of the required hot water load. Approximately 90% of the PV modules are situated on the roof of the building. The remainder of the modules and the solar thermal collectors are integrated into a custom carport that is reserved for low-emission–vehicle parking. The inverters are integrated into the employee’s staff room alongside a standalone kiosk to engage staff and visitors. 

The construction of the building core was mostly complete when RESCo began designing the array. This posed challenging space constraints as the building had very little capacity for solar on the roof. Working with an integrated and collaborative team, RESCo was able to provide a unique solution that added no additional loading to the roof deck. This required a custom flat-mounted system that tied the PV racking system directly into the building’s underlying structural support columns, suspending the solar array above the roof. Multiple sections were placed to help distribute the weight of the array over the building’s support columns. This reduced the power density but allowed the building’s core design to remain unchanged.

“This building was not designed for a solar array on the roof and as such caused some challenges during the planning stages. Our team had to get creative. We worked closely with the teams from LoyaltyOne and Bentall L.P.—the building owner—to provide a solution that met the needs of the landlord, tenant and contractors after the building construction had begun. The result is one of the largest rooftop arrays in Canada, on a building that was never designed to support a solar array.”

–Fidel Reijerse, president, RESCo Energy


LOCATION: Mississauga, Ontario, 43.6°N

Equipment Specifications

MODULES: 764 (48 carport, 716 rooftop) Sanyo HIT Power 205N, 205 W STC, +10%/-0%, 5.05 Imp, 40.7 Vmp, 5.54 Isc, 50.3 Voc
INVERTERS: 3-phase, 120/208 Vac service w/ 22 inverters: four SMA SB 5000-US, 5 kW, 600 Vdc maximum input, 250–480 Vdc MPPT range; three SMA SB 6000-US, 6 kW, 600 Vdc maximum input, 250–480 Vdc MPPT range; 15 SMA SB 7000-US, 7 kW, 600 Vdc maximum input, 250–480 Vdc MPPT range
ARRAY, FLAT ROOF: Eight modules per source circuit on two SB 5000-US inverters (1,640 W, 5.05 Imp, 325.6 Vmp, 5.54 Isc, 402.4 Voc), three circuits per inverter (4,920 W, 15.2 Imp, 325.6 Vmp, 16.6 Isc, 402.4 Voc); nine modules per source circuit on 12 SB 7000-US inverters (1,845 W, 5.05 Imp, 366.3 Vmp, 5.54 Isc, 452.7 Voc), four circuits per inverter (7,380 W, 20.2 Imp, 366.3 Vmp, 22.2 Isc, 452.7 Voc); 10 modules per source circuit on three SB 7000-US inverters and three SB 6000-US inverters (2,050 W, 5.05 Imp, 407 Vmp, 5.54 Isc, 503 Voc), four circuits per SB 7000-US (8,200 W, 20.2 Imp, 407 Vmp, 22.2 Isc, 503 Voc) three circuits per SB 6000-US (6,150 W, 15.2 Imp, 407 Vmp, 16.6 Isc, 503 Voc)
ARRAY, CARPORT: Eight modules per source circuit on two SB 5000-US inverters (1,640 W, 5.05 Imp, 325.6 Vmp, 5.54 Isc, 402.4 Voc), three circuits per inverter (4,920 W, 15.2 Imp, 325.6 Vmp, 16.6 Isc, 402.4 Voc)
ARRAY INSTALLATION: Conergy Suntop rails supported by custom framing on flat roof, 180° azimuth, 0° tilt; Conergy Suntop rails supported by custom carport, 151° azimuth, 35° tilt

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The PV design and installation at Edwards Air Force Base was executed across three separate sites. The 12,132 deployed modules were manufactured at Suntech’s Arizona factory and are compliant for procurement in American Recovery and Reinvestment Act (ARRA) and Buy American Act (BAA) projects. The individual systems are interconnected at the Base-owned distribution substations at 34.5 kV. The overall project was developed to meet the environmental compliance requirements of the National Environmental Policy Act and California’s Natural Heritage program, as well as requirements specific to the joshua tree and desert tortoise habitat conservation.

The US Air Force designated the site locations, amount of usable area and overall shape of the array footprint during the RFP process, prior to Borrego Solar’s involvement. Since the allotted land was determined prior to design, it was not optimized for the intended tracking solution. This presented a challenge when designing an optimized array configuration and layout.

In general, the most cost-effective installation for a single-axis tracker controlled by a centralized motor is to maximize the number of modules per tracker row (thus limiting the number of individual rows and racking materials), and at the same time maximize the number of tracker rows per motor (thus limiting the total number of motors and control circuits). These constraints are typically mechanical limitations of the system. However, when faced with the geometric constraints of the designated sites, Borrego Solar found it challenging to optimize both parameters.

For example, compared to the South Base site, the North Base parcel is longer in the north-south axis and narrower in the east-west direction. In addition, the site is off-azimuth, and area would be lost if the rows were installed with drive lines running directly east-west, as opposed to off-axis. To maximize rows at North Base, drive lines were installed at an angle that matched the overall site geometry. As a result, the allowable area was utilized to maximum efficiency, even though individual motors were slightly underutilized with regard to maximum mechanical capacity.

Borrego Solar maximized row lengths for further site optimization. Initial calculations from the tracker manufacturer indicated a maximum of 52 modules per row. However, with strings of 12 modules, there was significant benefit to pushing for 54 modules per row. Not only would that eliminate 4% of the total rows, it would also optimize string wiring by creating a regular stringing layout of 4.5 strings per row and optimize source-circuit combiner box sizing in relation to inverter inputs and row configurations. Working closely with Array Technologies, the tracker manufacturer, Borrego Solar was able to engineer a solution that allowed 54 modules per row, further optimizing the sites’ array capacity.

“One aspect of the design that presented a challenge was interfacing with the existing 34.5 kV electrical infrastructure on the base while still complying with Southern California Edison [the local utility] requirements for interconnection. During the design process, it was important to note which substations were fed from which utility feeders to avoid unintentional backfeed under low-load conditions.”

Frank Haslinger, Jr., Borrego Solar


DESIGNER: Ben Walter, senior design engineer, Borrego Solar,
INSTALLATION TEAM: Frank Haslinger, Jr., project manager, Borrego Solar; Phil Korycinski, construction manager, Borrego Solar; Toby Foster, project manager, Reno Contracting,; lead subcontractor: Carl Price, project manager, HMT Electric,; racking installation: Rick Lavezzo, owner, Arraycon,; mediumvoltage electrical installation: Rick Redmann, project manager, Southern Contracting,; inverter skid design and MV transformer integration: Hill Phoenix Power Systems,
DATE COMMISSIONED: December 21, 2011
LOCATION: Edwards, CA, 34.9°N
SOLAR RESOURCE: 5.7 kWh/m2/day
HIGH/LOW DESIGN TEMPERATURES: per Solar ABCs solar reference map: 104°F/14°F

Equipment Specifications

MODULES: 12,132 Suntech STP280- 24/Vd, 280 W STC, +5/-0%, 7.95 Imp, 35.2 Vmp, 8.33 Isc, 44.8 Voc
INVERTERS: 3-phase, 34.5 kV service; six Satcon Equinox 500 kW UL, 600 Vdc maximum input; 320–600 Vdc input voltage range; 3-phase, 200 Vac output
TRACKERS: Array Technologies DuraTrackHZ, single axis, gear drive, algorithm with GPS input tracking control method
ARRAY: 12 modules per source circuit (3,360 W, 7.95 Imp, 422.4 Vmp, 8.33 Isc, 537.6 Voc), 18–23 source circuits per combiner, 163–174 source circuits per inverter; 3.39 MW array capacity total
ARRAY STRING COMBINERS: Custom Process Solutions, DCB-xx- 4/12-TVSS, 15 A fuses
ARRAY RECOMBINERS: Inverterintegrated recombiners, 250 A, 315 A, and 350 A fuses
SYSTEM MONITORING: PV system and environmental monitoring provided by DECK Monitoring, additional metering and interface with existing SCADA system provided by Edwards Air Force Base

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The 1.047 MW Ferrisburgh Solar Farm (FSF) is currently the largest solar installation in the state of Vermont. Located along a highly trafficked road in close proximity to a local high school, it includes a significant educational component. The project also supports the local economy. Alteris Renewables and the entire FSF team were proud to make this project the first PV system commissioned under Vermont’s Standard Offer Program, a rebate structure designed to encourage the development of renewable energy projects.

The state obligated the team to acquire a Certificate of Public Good (CPG) for this project. Obtaining a CPG necessitates following a rigorous permitting process—the same required of electric transmission facilities, electric generation facilities and certain gas pipelines. Because a project of this size had never been done in Vermont, the team had to show local residents and town and state officials that the project would not adversely impact the community. They had to address concerns raised by state agencies relating to module reflectivity, inverter noise levels and storm water impact, among others. The team also worked closely with the electric utility, Green Mountain Power, to address interconnection and protection issues relating to MW-size PV installations.

One of the realities of designing a ground-mounted PV system in Vermont is that the significant annual snowfall must be taken into account. This presented the design challenge of balancing the optimal array tilt angle for snow shedding while avoiding significant inter-row shading. In addition, ample clearance under the array was necessary to attempt to prevent accumulated snow from obscuring the array’s lower edge. The final design specifies a 30° module tilt with 48 inches of clearance between the ground and the bottom of the array.

This system was instantly put to the test by a series of record snowfalls. The project was commissioned in late November 2010, at the beginning of one of the snowiest winters on record. Three months after commissioning, as the snow kept piling up, the owners had doubts as to whether the system would meet its energy production forecast. During many winter days, the modules were covered with deep snow or with snow and ice. However, as anticipated, they cleared off relatively quickly when the sun came out. Despite the record snowfall, the system is right on target for producing the projected annual energy generation.

“During the month of October, we received double the normal rainfall. As the clay field on which the system was being installed became saturated, machines were no longer an option for rack and module assembly. The majority of the array construction had to be managed with ladders. In spite of this significant obstacle, the job was brought in on time and on budget.”

—Jay Myrto, project manager, Alteris Renewables


DESIGNER: Adam J. Smith, director of electrical engineering, Alteris Renewables,
LEAD INSTALLER: Ken Mayer, Alteris Renewables
DATE COMMISSIONED: November 30, 2010 
LOCATION: Ferrisburgh, VT, 44.3°N
SOLAR RESOURCE: 4.24 kWh/m2/day

Equipment Specifications

MODULES: 3,806 Suntech STP275- 24/Vd, 275 W STC, -0/+5 W, 7.84 Imp, 35.1 Vmp, 8.26 Isc, 44.7 Voc
INVERTERS: 3-phase, 277/480 Vac service, two Advanced Energy Industries Solaron 500 kW, ±600 Vdc maximum input, ±330 to ±550 Vdc MPPT range
ARRAY: 11 modules per source circuit (3,025 W, 7.84 Imp, ±386.1 Vmp, 8.26 Isc, ±491.7 Voc). Inverter One: 186 source circuits total, with 93 positive and 93 negative-to-ground (562,650 W, 729 Imp, ±386.1 Vmp, 768 Isc, ±491.7 Voc). Inverter Two: 160 source circuits, with 80 positive and 80 negative-toground (484,000 W, 627 Imp, ±386.1 Vmp, 661 Isc, ±491.7 Voc).
ARRAY INSTALLATION: Fixed-tilt ground mount, Schletter FS System rack, 180° azimuth, 30° tilt
ARRAY STRING COMBINERS: 22 Cooper Crouse-Hinds model CCBF16F15DS200, 15 A fuses
ARRAY RECOMBINERS: Two Controls Engineering and Services model 27600, 225 A fuses
SYSTEM MONITORING: Draker Laboratories Sentalis 1000 Base Station, SHARK Energy Meter, weather station including plane-of-array irradiance, cell temperature and ambient temperature


Primary Category: 

Fluctuating hot water demand presents an interesting challenge for commercial water heating system design. In the Talbot County Public Safety Center, the average inmate population is approximately 100, but the maximum population can reach as high as 157. To solve the design challenge posed by this wide swing in demand, Aurora Energy developed a rooftop heat dissipation system to prevent system overheating during periods of low usage.

The array consists of 32 evacuated-tube collectors, with 30 tubes each, plumbed in two parallel banks of 16 collectors. A ballasted, nonpenetrating mounting system secures the collectors to the roof surface. Each of the two collector loops is coupled with an equivalent number of fin-tube heat dissipaters that are controlled by thermostatic diverting valves.

The system’s pump station was built at the site and consists of two pumps and one micro-bubble separator for each loop. Each pump has a dedicated controller. The first pump runs at a lower temperature gradient between collector inlet and outlet. The second pump starts at a higher temperature gradient and serves as a backup if the first pump fails. In addition, the second pump increases flow rate during periods of high solar insolation. The system’s heat exchangers and pumps are located close to the collector arrays to keep the glycol-circuit piping as short as possible.

“Manipulating tube numbers to manually increase and decrease the active capacity of the collector field to match inmate population would have placed an undue burden on the facility staff. The solution was a heat dissipation system that automatically matches solar hot water production with consumption, thereby eliminating the potential for system overheating.”

Mike Kabler, Aurora Energy


DESIGNER: Fariborz Mahjouri, PE, CEO, Aurora Energy,
LEAD INSTALLER: Mike Kabler, project manager, Aurora Energy
LOCATION: Easton, MD, 39.2°N
SOLAR RESOURCE: 4.6 kWh/m2/day

Equipment Specifications

COLLECTORS: 32 Solar Panels Plus SPP-30A evacuated tube, 52.7 sq. ft. each
HEAT EXCHANGERS: Advanced Industrial Components L-Line LA 14-50
PUMPS: 4 Grundfos UPS 26-99 FC
STORAGE: Existing 1,500-gallon tank
CONTROL & MONITORING: Thermo Technologies USDT 2005
FREEZE CONTROL: Closed-loop antifreeze, DOWFROST HD heat transfer fluid
COLLECTOR INSTALLATION: Nonpenetrating ballast mount on TPO roofing, 180° azimuth, 38° tilt


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