Show me what you got: Georgia Power demo project provides side-by-side solar PV module comparisons

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Tom Cheyney

Tom Cheyney is former senior editor of PV-Tech / Photovoltaics International magazine. A veteran technology journalist / editor / blogger, he covered the semiconductor, microelectronics and solar sectors for many years - since fax machines were state of the art. His PV-Tech blog has become a must-read for industry insiders and observers. He was also chief editor of "The Rise of Thin-Film Solar Technology" book published in early 2010.

Few tests reveal more about solar panels' comparative conversion efficiencies, power outputs, and the like than side-by-side performance evaluations. When Manufacturer A's monocrystalline model meets Manufacturer B's thin-film device in a cajon a cajon competition and the data are acquired and analyzed, no amount of marketing spin and handwaving can overcome findings from that kind of real-world throwdown.

Still, these demonstrations produce different results in different geographic locations. PV that works well under a moderately hot sun on a clear day may get its clock cleaned by another photovoltaic combatant in hotter or cloudier climes. Factors such as heat, humidity, and general solar insolation all have a bearing on a particular PV technology's performance--not just the inherent quality of the photoactive layers.

As it looks to solar as an increasingly important part of its green energy strategy, Georgia Power has commissioned a small-scale PV demonstration project that will give the utility and its customers as well as the PV module community new insights into which panels perform best in Atlanta and its environs. The company plans to have seven "representative" module technologies installed on its headquarters' roof, all with the same position and orientation to the sun, run them for a year, sort through and analyze the data, and see which ones perform best (and provide some clean juice to the building in the bargain).

Four of the seven ~4-KW arrays are already in place and generating electricity, with the fifth set to be put in next week, and the sixth and seventh systems scheduled for deployment later this year.

"Most of the data for PV is generated in the West, and not in the Southeast," explained Elizabeth "Liz" Philpot of the Southern Company, principal research engineer for the project, during a phone interview. "We need to know how the performance of these modules is for the Southeast," adding later that "we've got alot more diffuse light here than you do out west."

Ervan Hancock, Georgia Power's manager of renewable and green strategies, said during the same interview that "from a technologies standpoint, there wasn't real good, reliable data that we could have confidence in, from performance based on the heat and humidity within our peak period in the Southeast."

The project has its conceptual genesis in the early summer of 2008, according to Hancock. By late summer/third quarter, the module acquisition process had begun as well as site development. The roof itself didn't need much preparation, since the building was one of the most energy efficient of its kind when built in the 1980s, even sporting a solar thermal system (since removed) on the roof. The initial modules were installed where the leaky old CST system once stood in the first quarter of this year and were turned on about a month ago, he said.

Kyocera, SunPower, and Sanyo HIT crystalline-silicon modules as well as Uni-Solar amorphous-silicon thin-film laminates populate the first quartet of PV technologies already plugged in, noted Philpot. A panel incorporating c-Si cells made by Atlanta area company Suniva will be installed next week, while the remaining two slots will eventually be filled by copper-indium-gallium-(di)selenide (CIGS) modules from MiaSolé (which are "waiting to be certified," she said) and cadmium-telluride (CdTe) panels from First Solar. Each of the seven arrays will run through separate SMA inverters.

One goal of the Georgia Power demo project is to gather data about the modules' performance before the photovoltaically generated electricity flows through the inverter and is converted into alternating current. Hancock explained that because of the different technologies being evaluated, such before-and-after testing is critical. "We're monitoring metering on the DC side first as well, because there's optimization in the inverter side, but we want to see what the total power generated would be for each of those [panels], at the same angle and the same relative position."

Philpot said the last details of the project's custom data-monitoring system are "what we're working out right now" and that the system should be operational "within a month." Real-time performance information will eventually be displayed in a kiosk available to the public in the lobby of Georgia Power's corporate HQ, as well as via an online link.

The utility already has begun accumulating comparative info from the area's installed PV base. They are "metering and starting to get fidelity" on the various technologies among the 500 KW of solar already installed in its service area (40% commercial, 60% residential), said Hancock, all of which is part of a Green Energy tariff which offers renewable energy premiums to customers. "We hope to have a portfolio of comparable data that this [demo project] will support."

Once the remaining systems are plugged in, the data garnered from the Georgia Power research project will benefit the utility and its customers in their understanding the region's specific technology and economic options in their path to increased solar PV energy deployment. Although not of the sheer utility-scale drama of the side-by-side competition playing out in the just-activated 10-MW solar power plant in Masdar City, Abu Dhabi--where half of the field features Suntech c-Si modules, and the other half sports First Solar CdTe panels--that "pancake" rooftop in Atlanta will also provide some intriguing comparative data for the industry to chew on.