Panels located on roof of CCAT house
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## Module Testing

Because CCAT is part of a university, they have an interest in testing and evaluating systems. They made sure not to miss this opportunity with their new system. CCAT measured individual current versus voltage curves (I-V curves) for each of the eight ASE modules prior to installation. Although the donated ASE modules were reportedly manufacturer's "leftovers" due to cosmetic defects, they performed remarkably well. Their measurements showed that module output was within 1 percent of the manufacturer's measurements supplied with the modules, and within 2 percent of their nameplate rating. ASE uses a plus or minus 4 percent tolerance for rating the output of their PVs. Most other PV manufacturers use a plus or minus 10 percent tolerance rating. CCAT thinks that ASE's truth in advertising is laudable. ASE sets a high standard for rating the output of their PVs. CCAT hopes that the other module manufacturers will follow suit. The I-V curves were generated in ambient sunlight in Arcata, California near midday in June 2001, using an electronic DC load device. As the load was varied, the module traversed its operating curve from short circuit current to open circuit voltage. During the tests, CCAT also measured the radiation incident in the plane of the module as well as the module operating temperature. These measurements were then used to standardize the performance curves to STC. (See the module I-V curve.)

## System Installation

For a number of reasons, CCAT took a team approach to system installation. The CCAT house is an old structure, and the AC electrical wiring needed some work to bring it up to code before they could reconnect to PG&E. CCAT had Peter Brant, a local electrical contractor, perform this work. While he was at it, the team had him install the AC disconnect for the PV system, prepare the AC panel for interconnection, and run the AC wiring from the inverter room to the AC disconnect. CCAT had Bob-O Schultze, a solar-electric contractor, run the DC wire and conduit, assist with the inverter and PV module installation, and ensure that our installation was code compliant. They installed the array mounting structure, PV modules, and inverters themselves, with help from students in a PV Design and Installation class offered through the Environmental Resources Engineering Department at HSU. The equipment we chose allowed for a rather quick and easy installation procedure.

The RoofJack mounting system is designed for pitched asphalt shingle roofs like CCAT's. It supports the modules about 3 inches (7.6 cm) above and parallel to the roof, allowing for adequate air circulation between the modules and the roof to promote module cooling. The RoofJacks came complete with self-drilling fasteners (21/4 inch, #12) and sealing washers, preapplied butyl-rubber sealing pads, and pipe nipples for wire pass-through between modules. Their eight, large area modules were installed in one continuous row. Each module is supported by four RoofJacks, one placed near each of the module's four corners. There are two types of RoofJacks—end and interior. They used four end RoofJacks at the extremities of the array. A pair of shared interior RoofJacks support the module edges that are located next to other modules, for a total of 14 interior RoofJacks. To properly locate the RoofJacks on the roof, they built a jig with the bolt hole pattern for one set of RoofJacks. After installing the first set, CCAT simply moved the jig over and installed the next set, and so on. According to the manufacturer, securing the RoofJacks directly to the sheathing (a minimum of 5/8 inch; 16 mm thickness) is adequate, but they felt that it was prudent to add reinforcement. The team located the array on the roof so that four of the interior RoofJacks were secured directly to two rafters. To secure the remaining RoofJacks, they either scabbed 2 by 4 blocks to a rafter or added strips of plywood sheathing on the underside of the roof sheathing to provide a more secure attachment. Once the RoofJacks were installed, the modules were outfitted with their mounting bolts. Four bolts were attached to each module, two on each side near the corners. These bolts protrude about 1/2 inch (13 mm) with a sleeve. To install the modules, they simply lifted them into place and slid the four mounting bolts into slots on the RoofJacks. Wiring the array was just as easy. CCAT's system consists of two separate subarrays, each comprised of four modules wired in series and connected to an inverter. The first set of four modules in the row make up one subarray, and the second set of modules make up the second subarray.

Fig. 4 Panels located on roof of CCAT house

## System Performance

The new grid-connected PV system first started generating on October 17, 2001. Of the 901 KWH total solar-electric energy generated as of April 23, 2002, 358 KWH were used on-site, and the other 543 KWH were fed back into the PG&E grid. During this period, they averaged 1.9 KWH per day of electrical energy use, while the PV system generated an average of 4.8 KWH per day.

Fig. 5 Panels in action when CCAT was at its original location

Data for about a one-month period in mid-February to mid-March of 2002 was examined to evaluate the performance of the system. During this period, the PV system generated an average of 4.9 KWH per day. The maximum AC power output was 1,745 W, with a corresponding maximum DC input power of 2,155 W (81 percent average inverter efficiency). The inverters, with a rated peak efficiency of 93 percent, averaged 83 percent and 85 percent, respectively. About 99 percent of the time, the input voltage to the inverters was within their maximum power point tracking range of 55 to 70 VDC. Inverter efficiency varies as a function of AC power output. (See the inverter efficiency plot.) The highest points in the graph are clearly aberrations in the data. However, there are over 1,400 total data points, of which only 30 show efficiencies greater than 96 percent. In all cases, these abnormally high efficiency readings are recorded at very low power outputs (always less than 171 W). Since startup, CCAT has experienced only one minor problem—a blown fuse on the DC input to the inverter. They suspect that this was due to enhanced insolation conditions associated with cloud reflection. The team are very pleased with the performance of their new PV system and our decision to reconnect to the grid. They do realize that their reconnection to the grid threatens to make them less aware of their energy use patterns and lax in their energy efficiency efforts. So they are making a concerted effort to keep track of their usage and to maintain their efficient ways.

## References

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Type Project photovoltaics, ccat active project SDG07 Affordable and clean energy Michael Crosbie, Anh Bui, Dominick Triola, Zane St. Martin 2011 CC-BY-SA-4.0 Cal Poly Humboldt, Campus Center for Appropriate Technology (CCAT) CCAT PV system/OM Michael Crosbie, Anh Bui, Dominick Triola, Zane St. Martin (2011). "CCAT PV system". Appropedia. Retrieved August 19, 2022.
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