Solar

Automating PV Module Assembly: Machine Beats Man

Issue 3 and Volume 2.

For module assembly, the ability to automate production of any type of panel reflects the maturity of industrial robotics, says Tim Metko, KUKA Systems. For manufacturers in the more established crystalline-silicon (c-Si) sector, automation is helping them face pressures, such as more competitively priced Asian-made panels.

(July 20, 2010) — For module assembly, the ability to automate production of any type of panel reflects the maturity of industrial robotics, says Tim Metko, KUKA Systems. For manufacturers in the more established crystalline-silicon (c-Si) sector, automation is helping them face pressures, such as more competitively priced Asian-made panels.

Manufacturers are in a race to produce PV panels for the lowest possible cost, which is fueling a trend towards large, highly automated operations with huge economies of scale. Several years ago, a good-sized PV module plant manufactured 25MW of panels a year. Now, plants are being built to produce 100MW, 200MW, 500MW, and up. A fully automated, 640MW assembly line near Berlin, Germany, for example, is capable of producing a CIGS foil thin-film panel every 10 seconds.

For manufacturers in the more established crystalline-silicon sector, automation is helping them face pressures that seem to be coming from all angles: more competitively priced Asian panels (reflecting lower labor costs), diminishing government incentives in some countries, uncertain support in others and competition from newer thin film technologies, with medium-efficiency panels that take dead aim at their traditionally higher-cost, higher-efficiency ones. Already, some thin film producers boast manufacturing costs below $1/W, or less than a quarter of the cost of producing a c-Si panel just three years ago. It is now widely accepted that manufacturers of commodity panels throughout the developed world will have to rely on large-scale automation, especially if they want to compete in export markets.

Automation fits all types of PV operations

Automation is being applied to all PV cell types and module sizes: cadmium telluride (CdTe) and copper indium gallium (di)selenide CIGS, mono- and polycrystalline, and concentrated PV (CPV), liquid or solid encapsulants, and any type of layup. PV module manufacturers can choose to automate their entire module assembly process or cherry-pick custom engineered solutions to automate the most labor-intensive or highest scrap-producing areas first. An annualized capacity of ~50MW seems to be the cut-in point where full-line automation becomes economically attractive. One can automate a c-Si module line at 25MW but the automation itself will only have  utilization rate of  55-60%. At 50MW, utilization jumps to the mid-80s. A plant with two parallel 80MW lines sharing the same pack-out station for finished panels can get into the 90-95% range. The staffing ratio for a fully automated module line versus a largely manual line can be as high as 1/13. Our analysis of one US firm’s 100MW expansion suggested automating module assembly would save $12-14 million annually on labor alone. (Depending on each plant’s circumstances, it takes 10 to 48 months to achieve a 100% ROI through labor cost savings — two years is fairly typical.)

For thin film manufacturers, automation provides clean-room type handling systems essential for that kind of high volume production. For c-Si manufacturers, there are automated brick and wafer lines. Advanced wire saws can slice ingots of silicon, germanium, GaAs, InP, glass, ceramics and ferrites into the thinnest wafers ever, reducing silicon usage, energy consumption and the cost of consumables while producing a better surface quality for cell production.

Maturity of robotic technology and adaptability

For module assembly, the ability to automate production of any type of panel reflects the maturity of industrial robotics. The basic robots used in solar automation systems are stock items found in automobile assembly, warehousing and logistics, food processing, aerospace manufacturing and any number of other industries. (When a module line outlives its mission, these flexible automation pieces can be taken apart and reassembled almost anywhere, or the equipment resold piecemeal.)

The value-added benefits that a full-service integrator brings to the table include designing customized turnkey lines, performing system throughput simulations, selecting the proper robots and dressing them with specialized end effectors — the sophisticated tooling systems on the robot arm — and choosing the appropriate peripherals and software to perform specific tasks, either as standalone automation cells or in work groups.

Figure 1. Automated cell production: a KUKA Robo X. SOURCE: KUKA Systems

For c-Si panels, robots have been assuming functions previously done manually, like cell stringing and string layup — where cells are arrayed in rows, connected by means of small bus bars, and laid out on an encapsulate for cross-tie soldering. For example, the Robo X (Fig. 1) is a three-robot station that can solder up to 28 bus bar ribbons along the panel edge in 80s, a job that typically takes anywhere from six to eight workers per shift. One robot positions cut-to-length bus bar ribbons in magazines for two larger robots to place and precision solder. After this sandwich is laminated, other robot work stations perform all functions to complete the module, including trimming, taping, framing, potting and packout.

Automated testing pre-empts problems in the field

A typical fully automated line producing 450,000 panels per year would have 15-20 robots and eight or nine testing stations to verify cell quality and module integrity. Automated testing can detect defects that visual inspection misses. For example, the String TMP (Fig. 2) performs two essential cell tests in a single step: an optical test to verify the alignment and spacing of cells in a string, and an electroluminescence test that can detect micro-cracks invisible to the naked eye that would only begin impacting performance when the panels are installed in the field and costly to repair.

Figure 2. String testing cell. SOURCE: KUKA Systems

Robotic assembly produces a consistent, high-quality module day and night with an order of magnitude fewer rejects than if the build was done manually. By employing vacuum and ultrasound technologies, robots can handle the thinnest, most fragile cells with minimal breakage. These robots can also pick up and swivel a large, heavy sheet of glass in a very tight turning radius.

Conclusion

A full service integrator draws on its engineering expertise as a designer of turnkey assembly lines to implement the most efficient and cost effective module line. Turnkey doesn’t mean off-the-shelf.  While various integators module assembly lines may look alike on paper, understand that every automated module line is a little bit unique and involves a considerable amount of custom engineering. Every PV module maker has a little different mousetrap: how they solder their cells together, which junction box they use, what inspection processes they use – strictly optical or electro-luminescence, too. The integrator must consider these different product variations in the design process and then perform virtual simulations of the design to avoid potential bottlenecks and optimize product flow throughout. The installation also has to conform to local electrical and safety regulations, as well as all applicable standards and certifications.

Tim Metko received his BSWE from Ohio State U. and is currently a sales engineer for the Alternate Energy business unit at KUKA Systems Corp North America, 6600 Center Drive, Sterling Heights, MI, 47312 USA, [email protected]; phone +1 586 795 2000 x4149; www.kuka-systems.com