Here’s a pair of terms that you don’t often see together-- “concentrating photovoltaics” and “commercial rooftop solar market.” The image of a large, free-standing CPV tracking system anywhere but on terra firma doesn’t usually enter the mind of the average system designer or integrator. But what if the concentration units came in a form factor that lent itself to rooftop applications, with the benefits of CPV’s “it’s all about the kilowatt-hours” high energy density capabilities and a total system cost that could make a serious run toward the more economical end of the mainstream PV spectrum?
At least one company thinks its version of CPV belongs on the roof, specifically the top-sides of warehouses, distribution centers, state buildings, and similar structures. Soliant Energy aims to deploy its concentrator panels in 50KW to 1MW distributed-generation arrays on millions of square meters of commercial, industrial, government, and carport upper-deck real estate in the sunny, dry American Southwest and, eventually, similar climatic regions on the planet.
When I took in the view from Soliant’s own rooftop during my recent visit to its Monrovia, CA, headquarters, the surface was populated with several test beds of panels (the company’s Gen-1 and Gen-2 models as well as some competing panels), inverters, and test gear, with the San Gabriel Mountains a stunning backdrop just a few kilometers to the north. The company’s CPV units look somewhat like their crystalline or thin-film flat-plate cousins—although the blunt-contoured, white-bucket bodies resemble a large turkey-basting pot more than a shallow metal box—and the devices’ design allows for them to be installed in a similar fashion to more traditional systems.
The Soliant folks have come up with their own variation on the “module vs. panel” PV nomenclature conundrum. What they call a “module” includes eight receiver assemblies consisting of a high-efficiency multijunction Spectrolab or Emcore cell, two-level Fresnel 500X concentrator optics from 3M, a heat sink, and printed circuit board. Each module is also individually integrated with the company’s proprietary TipTilt two-axis tracking system, which through its combination of inexpensive but reliable motors, movement sensors, and unique algorithms can track the sun through the course of the day with a pointing accuracy of 0.1%.
A six-pack of these modules—called a “panel” in Soliant-speak and currently rated at 369W--are racked in sequence in a lightweight (about 110lbs) system that is wind resistant, compatible with existing rooftop schemes, and requires no field wiring. Although there needs to be a minimum of 40 inches, center to center, between the panels, they can be spread out as needed, depending on the roof setup and weight-load specs. Shading issues are proportionately mitigated with a wiring package that makes the system more tolerant when a module has its photons impeded.
Before taking me to the roof, Soliant’s Jason Bobruk showed me the inside testing area, where the tracking actuators are going through the rigors of 10X life-cycle reliability and four Thermotron chambers put the modules through their paces of UL- and IEC-type environmental exams. The company director of applications engineering (who also is an IEC standards committee member) told me that by pretesting the devices in a serious fashion, the actual UL process goes smoother. The company’s modules are in the midst of official UL testing, which should lead to certification in the first half of 2010, according to my other tour guide, Jay Goldman, the firm’s VP of sales.
The company’s newly minted 1MW pilot line is a few doors down from HQ. A mostly manual assembly line puts the wires and receiver assemblies in the “buckets,” the lenses are placed, then a robot seals them up. The modules on the line are set for shipment to the initial six beta sites by the end of October, Bobruk said. Soliant puts together the receiver assemblies itself and contracts a local company to fabricate the aluminum tracker racks, several rows of which were lined up on the factory floor.
When the company opens its first volume line, the process flow will be about 85% automated, said Bobruk, featuring “off-the-shelf” robotics. The production tools have been designed and are being built at Soliant’s equipment partner. The manufacturing systems will have a relatively small footprint and cost, according to my hosts.
Back at the main building, Bobruk, Goldman and I meet with one of Soliant’s latest hires, the company’s new chairman/CEO, Terry Bailey, who most recently was a senior VP at Evergreen Solar. Before considering taking the job, Bailey said he wasn’t aware of anyone doing CPV on rooftops, “To me, the roof space has always been one of, how do you optimize the energy you can get off this underutilized potential revenue stream,” the exec explained, “so I thought it was a really unique focus.”
Another aspect that Bailey found interesting was that “by necessity, Soliant from the beginning had to think about the system. They really thought through things like the wiring, BOS costs, etc. The design lends itself to expansion and can work around things on a roof that might not be ideal for flat plate.”
Bailey also was drawn to what he sees as economic and regulatory advantages of Soliant’s focused strategy. “Since it’s a flat-roof space, the environmental hurdle is low or nonexistent. The financing hurdle is much smaller as a gross amount of money necessary, and it’s generally going somewhere people have some vested interest in either mitigating their energy cost or wanting to do the right thing for the environment—and they have a perfect place to do it.”
Goldman booted up a presentation detailing Soliant’s “highest energy density and lowest levelized cost of energy” message. Like other CPV approaches, the company can point to 20-30% more kilowatt-hours per system compared to stationary, nontracking installations. One slide featured a Phoenix-area rooftop daily energy output comparison of Soliant’s panels with monocrystalline, polycrystalline, and cadmium telluride units, revealing a hundreds of watts performance gap between the CPV and its closest competitor—with a pronounced difference in the late summer afternoon hours when peak power needs are at their, well, peak.
Bobruk (who's shown at right, with Goldman on the left, in the above photo taken on the Soliant roof) emailed me later with more information about the methodology. “The daily comparison was done through a simulation using PVsyst 4.37. The poly and mono panels are on a 10° fixed tilt and the thin film was flat. We wanted to compare to typical rooftop installations. The simulated system size was 250 kW but is actually irrelevant for that graph which represents 1 m2 of roof area. For AC energy, the numbers could simply be multiplied by some average inverter efficiency, say 0.95. The intent of the graph is to compare only the DC module/ DC panel assuming the same inverter would be used and offer the same performance in either case.”
Bailey has only been on the job for a few weeks, but he’s joined the team at a critical juncture, when the knowledge and insight gained from his days as part of the senior team at the string-ribbon king will come in handy.
With the pilot line open and beta shipments imminent, the company is busy checking out sites for a factory in the western U.S., and hopes to have that site selection process completed by the first half of next year. Once its products get UL certification, Soliant wants to put its first 7MW or more of capacity online (once financing and/or a DOE loan comes in) and start shipping its SE-500X systems in earnest. By the first half of 2011, a full-scale production capacity of 25MW is envisioned.
Although the internal challenges facing a start-up like Soliant are not insignificant and Bailey certainly can bring his Evergreen factory-ramping and company-building experiences to bear, he sees external issues as an even greater challenge. “It’s really a matter of getting people used to putting CPV, motors, moving things, on the roof—which is why the beta sites are so important--having a belief system that it will last the length of time that people have come to expect of solar.”
Is the high energy commercial or government consumer ready to take a risk and put CPV on its rooftop? Will those with limited space in San Bernardino opt for a system that will maximize the energy output per area, or the potential customer in Las Vegas with a limited budget want to get as much energy bang for his buck as possible on his tens of thousands of square feet of near-empty top-floor space?
Like the rest of its colleagues in the CPV sector, Soliant must now execute on the game plan and prove it can manufacture and supply a reliable, powerful system at a competitive price point. If it succeeds, the team from Monrovia will be shouting from the rooftops.
Soliant is exhibiting at Solar Power International at Booth 1100
PHOTOS BY TOM CHEYNEY