Bosch Solar Energy in San Mateo, Calif., manufactures crystalline silicon and micromorph thin-film solar modules. The Bosch Proving Ground, an automotive testing facility in Flat Rock, Mich., proved to be an ideal geographic location to install 50 kW worth of the company’s ground-mount photovoltaic technologies. To speed up the installation, the company used a slide-in mounting system featuring aluminum structural framing from another member of the Bosch Group, Bosch Rexroth Corp., located in Hoffman Estates, Ill.
The Proving Ground, a controlled environment used for evaluating automotive technologies installed on cars, trucks, motorcycles and other vehicles, features a 1.4- mile test track loop with a three-lane banked turn and a 25-acre vehicle dynamics pad with a hydroplaning surface. The campus offered plenty of space with few interfering tree lines. In addition, the facility receives a large amount of sunlight throughout the year and has a significant amount of open space available for a large number of solar modules.
“Generally speaking, solar panels are mounted on rooftops or on the ground,” said Helen Nigg, director of sales for Bosch Solar Energy. “However, if they are mounted on top of buildings, there are space constraints with structures on the roof, like HVAC units and skylights. The Proving Ground had plenty of land to use, and the facility is in an ideal spot.”
The solar installation, which encompassed nearly 20,000 square feet, included one array of crystalline silicon modules and two arrays of micromorph thin-film solar modules. A subsidy from Michigan utility provider DTE Energy partially funded the project.
The first thin-film array — arranged in a 10,670 square foot area — included two rows of 189 modules each measuring about 51 inches by 43 inches. The modules consist of thin photovoltaic film placed between two pieces of glass. The second thin-film array, using about 5,800 square feet, contained 96 thin-film modules in two rows. The crystalline silicon array — about 3,000 square feet — contained two rows of modules. Each measures about 65 inches by 39 inches.
While crystalline silicon has traditionally been used in photovoltaic technology and can easily convert sunlight to energy, thin-film modules are less costly to produce and can provide excellent energy yields in low light. Both solar technologies were used in the installation to facilitate real-time data collection on the performance and efficiency of each type of solar technology in various sunlight and cloud-cover conditions. Based on this data, Bosch Solar Energy can best determine which technology would best suit a client’s particular location or application.
The question for the engineers was how to make this installation as cost-efficient as possible. That’s where its sister company, Bosch Rexroth, offered a solution.
To help reduce installation time on the project, Bosch Solar Energy opted to use a slide-in module mounting system made with Rexroth aluminum structural framing and designed specifically for installing micromorph thin-film solar modules.
The aluminum structural framing portfolio contains over 120 different lightweight and load-bearing profiles that can be easily configured for diverse applications, ranging from lean manufacturing workstations to architectural framing for sustainable residential housing. The aluminum profiles can be assembled into any arrangement required without using specialized tools. The framing is adaptable for each solar installation based on the physical environment and space limitations with no need for complex engineering.
“One of the benefits of using extruded aluminum profiles is that we can tailor the shape and dimensions of them to meet a customer’s requirements,” said Kurt Greissinger, product manager for Bosch Rexroth. “As soon as we understood the application needs, we designed a particular aluminum profile product to meet the specifications of the micromorph thin-film solar modules.”
The solar panel mounting system features variable track lengths, bracket spacing and insert dimensions. The aluminum profiles range from 30 mm x 50 mm to 45 mm x 90 mm. Together with the slide-in track, the system forms a complete unit that securely encloses the modules. The module structure enables the micromorph thin-film solar modules to withstand force up to 2,400 Pascal, corresponding to 770 pounds of weight acting on the module.
“The entire system is tested, proven and reliable,” Greissinger said. “Not only is the framing easy to install, but once it’s in place a team of a two people simply slide the glass into the sleeve, like stuffing an envelope, and another team of two people tighten the brackets. The system cuts installation time in half to 15 seconds per module, meaning twice as many modules can be installed in the same amount of time using this slide-in technology vs. conventional four-point clamping.”
Traditionally, solar panels were installed by bolting clamps into the aluminum frame and tightening them to hold the solar panel to the frame. Since installation brackets and clamps are no longer required, material costs are also reduced by about 40 percent.
Another component of thes system is a small, thin C-shaped plastic insert placed over the edge of the glass. The plastic protects the glass from coming into direct contact with the aluminum frame. It also facilitates smooth installation into the C-channel of the mounting profile and can be customized to accommodate solar modules of various thicknesses. Rubber-coated stops are bolted to the underside of the aluminum frame where the glass rests when it is installed.
Greissinger added that the aluminum structural framing is rugged and weather-resistant, which not only contributes to the durability of each installation but also helps aesthetically because it continues to look clean and neat over time without additional painting or other maintenance.
The crystalline silicon modules, which come pre-assembled into aluminum frames, did not require the same custom slide-in system as the micromorph thin-film modules. However, Bosch Solar Energy used off-the-shelf Rexroth aluminum framing for that array.
The installation is expected to generate 63,400 kW hours a year, or up to 15% of the testing facility’s energy needs.
“Since the facility has relatively low energy requirements, the ability to generate 15 percent of their energy requirements from the installation is pretty significant,” Nigg said. SPW
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