The U.S. has set 2015 as a goal to reach grid parity, which means the point in which solar electricity is equal to grid electricity. Many other nations predict reaching it as soon as 2010. But no matter what your thoughts on regulatory involvement, it is clear there will be a resurgence in investment, development and innovation within the photovoltaic (PV) manufacturing community throughout the world -- and it will largely be driven by technology.
Finding the most effective tools and processes is paramount. While the significance of robot automation in the manufacturing of solar cells is obvious, determining which fits a specific process may not.
Robotic Automation's Impact
Robots in the photovoltaic manufacturing process are important due to their ability to significantly reduce costs while continuing to increase their attractiveness compared to manual labor. Richard Swanson, CTO of SunPower, a large-scale manufacturer of solar technology, described automation's impact through the prism of economies of PV manufacturing in terms of labor.
According to Swanson, to produce one gigawatt of solar power it requires 250 to 500 laborers to produce polysilicone, 250 to 500 laborers to process ingots, 3,000 to 6,000 people to manufacture the cells, between 1,500 and 3,000 for the panel lamination and associated applications and between 2,500 and 5,000 for the solar system integration. In total that's anywhere from 8,000 to 16,000 laborers required to produce 1GW of photovoltaic capacity.
Therefore, to produce 500GWs of solar power per year equates to roughly 4 million people who could be adding tremendously more value in other capacities. With more automation, inclusive of appropriately applied robotics, the solar industry can cut that labor to 1 million people realizing a 75% savings in direct labor costs alone. Given this magnitude it is critical robots receive ample consideration in line design.
Selection Considerations
A handful of considerations will provide good direction in selecting the correct robot. First and foremost, what is the payload requirement for the robot? Frequently people only consider the products that are being handled. However it is important to also consider the tooling solution or end of arm tool (EOAT).
Evaluating the motion requirements is also critical. Not only the simple motion of picking and placing, but also what interferences exist between the robot, its linkages as well as other items that may be in dynamic motion within the cell.
Consideration must also be given to how parts are produced and throughput requirements. Repeatability is also an important factor and it should be understood that robot manufacturers tend to speak in terms of repeatability, while engineers and designers tend to look at it from the standpoint of accuracy. A robot's repeatability outlines the machine's ability, once taught, to return to that taught position. Accuracy references the ability to input a given location digitally and have the robot move to that point in space "accurately." Accuracy, therefore, encompasses offsets and other digitally inputted motion parameters and often varies within a given mechanical unit's work envelope. Thus, a good understanding of a process's requirements in combination with the capabilities of a given robotic solution requires careful evaluation.
Major Robot Types
Robot kinematics can be divided into four major categories: Cartesian, SCARA (selective compliance assembly robot arm), articulated and delta/parallel.
Cartesian The Cartesian kinematic solution is highly configurable as the platform includes everything from a single degree of freedom or unidirectional travel, to numerous axes of motion. Cartesian solutions have numerous applications within the PV industry. They can be applied to both small and large workspaces. An example of a job using a small Cartesian robot might be dispensing sealing material on the flange of a junction box. The sorting and placement of solar cells in a large rectangular is also an optimal application for a Cartesian. Solar cell sorting into multiple stacks in a large work area and processes such as stringing up and lay up within a large cubic area where robots are required to reach with good repeatability are optimum applications for a Cartesian robot.
SCARA The selective compliance assembly robot arm (SCARA) robot typically provides higher speeds for picking, placing and handling processes when compared to Cartesian and articulated robotic solutions. They also deliver greater repeatability by offering positional capabilities that are superior in many cases than those of articulated arms. This class of robot is usually used for lighter payloads, such as 10,000 pieces or less, for applications such as assembly, packaging and material handling.
Within solar manufacturing processes, these robots are best suited for high speed and high repeatability handling of cells in smaller workspaces. They are often found in junction box handling and assembly of panels.
Articulated Articulated robots have a spherical work envelope. These arms offer the greatest level of flexibility due to their articulation and increased numbers of degrees of freedom (DOF). This is the largest segment of robots available on the market. Articulated robots are frequently applied to process-intensive applications where they can utilize their full articulation and dexterity for applications such as welding, painting, dispensing, loading, assembly and material handling.
Articulated robots are applied in many solar applications, such as handling heavy silicon ingots which are also in an area where the robots might require industrial protection, and handling wafer cassettes where the orientation of the carrier might differ from pick to place utilizing the full dexterity of the robot.
Delta/parallel Parallel robots provide a cylindrical work envelope and is most frequently applied to applications where the product remains in the same plane from pick to place. The design utilizes a parallelogram and produces three purely translational degrees of freedom driving the requirement to work within the same plane. Parallel robots offer high-speed transfer of solar cells through manufacturer lines and a multitude of processes. Three examples are diffusion of process equipment, wet benches and PECVD anti-reflective coating machines.
Flexibility with Vision Vision has become a highly adopted tool to improve the productivity of robot automation in all industries and all facets of placement. Vision systems offer tremendous flexibility for applications that don't require fixtures or trays for part location.
Different part geometries only require vision re-training or the selection of a recipe instead of manual changes in fixtures and tooling, which increases the overall lifetime profit of the equipment by virtue of its optimization and improved throughput. Most robot manufacturers offer packages with multiple cameras and tracking solutions for integration into a single cell, which offers tremendous power and flexibility for solar manufacturing.
The common goal for solar manufacturers is to drive down the cost per watt. History has shown that automation has played a significant role in reducing manufacturing costs in many industries. When the costs associated with higher quality and yields are considered, the benefits of automation offer even more value.
As the solar sector scales for increased demand, many manufacturers in solar are looking outside their industry for the best practices in high-volume manufacturing. Automation and robotics is one answer to achieve that cost reduction.
Rush LaSelle is director of worldwide sales and marketing at robotics manufacturer Adept Technology.
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