HelioVolt Corporation, based in Austin, Texas, makes high-efficiency thin-film solar modules for the commercial rooftop and utility markets. Despite photovoltaics (PV) being one the fastest-growing energy technologies, the recent decline of price levels in the worldwide thin-film solar cell market has forced manufacturers to accelerate the development of more efficient thin-film technologies, re-engineer production processes and streamline their operations to stay competitive.
The most promising of the thin-film photovoltaic materials in the industry is CIGS (Copper Indium Gallium Selenide), with record efficiencies having reached silicon performance levels of 20.1 percent as reported by ZSW of Stuttgart and verified by Fraunhofer ISE.
Thin-film manufacturers today, like those producing CIGS modules, require highly-automated systems to arrive at the cost efficiencies needed to compete on the world market. Thin-film PV manufacturing processes must provide continuous high-speed throughput while maintaining zero defect rates, and be capable of shifting production volumes quickly with minimal set-up times.
Streamlined Panel Movement
In 2009 HelioVolt opened a 125,000 square-foot, 20 megawatt capacity production plant in Austin, Texas. Through every step of the process—from receipt of incoming flat glass to the two stages of CIGS semiconductor deposition, to the assembly of the final modules and testing, and finally packaging for shipment—the plant is a showcase for streamlined CIGS manufacturing and throughput.
Transporting the CIGS panels to the production processes throughout the plant, and providing precision infeed and take-away of the glass panels for these systems required an integrated flow of material handling systems to accomplish seamless throughput. To design and implement this material handling system, HelioVolt brought in Shuttleworth, Inc. This company has a long history of providing material handling systems, such as conveyors, accumulators and buffers, for transporting flat glass, and solar panels and modules, as well as for the transportation of other electronic components and assemblies.
“The factory line was designed in collaboration with a number of partners, including Shuttleworth,” says John Prater, Vice President Supply Chain with HelioVolt. “From the initial receipt of the flat glass into our plant, it is loaded onto the automated conveyor system. As the glass goes though each of our processing steps, through to the end of the line, the conveyors are transporting the glass panels.”
More than 1,000 linear feet of automated conveyor systems were custom-designed and installed into the HelioVolt plant to interface with the facility’s robots and automated production equipment. A multitude of custom devices and mechanisms were incorporated throughout the system to stop, buffer, transfer, rotate, and raise and lower the 4-foot x 2-foot panels.
The conveying system utilizes an open roller and roller-shaft surface design throughout the facility. This allows devices to easily be positioned from underneath, enabling the CIGS panels to move without interference. Product stops, product positioning clamps and photo eye sensors were all mounted below the roller surface and came up underneath the rollers to access the panels.
Lift-and-rotate (LAR) devices are used to change the orientation of the panels on the conveyors. The LAR devices rest just below the roller surfaces until activated. The CIGS panel is conveyed to a product stop, which positions it over the LAR device. The LAR, activated by a sensor, then lifts the panel above the roller surface before rotating it to the desired orientation. The LAR device then lowers the CIGS panel to the conveyor surface where it is conveyed in its new orientation.
Lift-and-transfer (LAT) devices installed in the material handling system are used to provide a smooth and accurate CIGS panel transfer at a 90-degree angle to the original transport direction. The LAT mechanism is mounted within the conveyor frame and consists of two or more mini-belt conveyors that reside below the roller surface when deactivated. Upon activation, the LAT device lifts the product above the conveyor surface and transports it 90-degrees in either direction to a predetermined point. Lift-and-transfer devices can transport panels precisely to multiple conveyor lanes based on HelioVolt’s panel/order identification tracking system.
HelioVolt’s conveying system is also equipped with Slip-Torque technology which provides low line pressure throughout the continuous-motion accumulation conveyors. This allows for precise product placement and virtually eliminates CIGS panel damage by creating low back pressure.
Should the line need to slow or stop, the conveyors can continue to take panels from the upstream line for a specified period of time instead of stopping the line. A low-pressure accumulation buffer absorbs irregularities in the production flow, and provides a smooth, even flow on the line.
Slip-Torque utilizes individually-powered rotating roller shafts and loose-fit rollers, which become the conveyor surface, powered by a continuous chain to control the drive force. The size and weight of the panels determine the driving force and roller selection. When the CIGS panels stop on the surface of the conveyor, the segmented rollers beneath the cells also stop.
“A critical factor in the selection of the material handling system was based on total cost of ownership,” Prater says. “The Shuttleworth system represents an excellent long-term process solution to the production throughput challenges encountered in our plant.”
Jim McMahon writes on automation technology. He can be reached at [email protected].