Conveyer belts and robots then move each panel down the line to one of three additional vapor deposition chambers, where it is coated with a film of multicrystalline silicon. This layer absorbs red light, allowing the panels to take advantage of more of the energy in sunlight. Forming multicrystalline silicon takes time and care, but having three systems perform this step on different panels in parallel keeps it from slowing down the entire manufacturing process.
Moving down the conveyer belt, each panel goes through another laser scribe to carve the silicon films into cells whose boundaries align with the patterns in the conductive layer. The panels are then coated with three layers of metal that act as a back electrical contact; after another scribing step to shape a contact for each cell, they are nearly finished. If the manufacturer wants to cut the giant panels in half or even into four pieces, that happens at this point. Then, to ensure that a person who touches the edges of the finished panel won’t get electrocuted, the borders of the conductive areas are edged off and the glass is reseamed to fill in the space.
Next, a top piece of glass is laminated to each panel in a process similar to that used in making car windshields. Finally, a junction box for carrying electricity from the panel is added to the back. Each completed panel is exposed to a solar simulator to test its output and then marked with a performance rating.
When Applied Materials started producing equipment for making the large modules, many in the business assumed that each panel would be sliced into smaller pieces, says John Benner, manager of PV-industry partnerships at the National Renewable Energy Laboratory in Golden, CO. But the company made a good case for leaving them intact. Because of their large area, the modules have among the highest power outputs in the industry–about 500 watts. The large size leads to savings on installation costs that help the panels compete with other thin-film systems on the market. The cost of electricity generated by the giant panels is $3.50 a watt, including installation.
Panels of this size are best suited for use in massive ground-based solar farms. Several such facilities have already been built, including a 500-kilowatt farm in Neustadt, Germany, that contains thousands of modules. Seven factories equipped with the technology are up and running at full volume and have manufactured more than a million of the modules.
The next challenge Applied Materials has set itself is to bring manufacturing costs down to $1 per watt by the end of this year. Its thin-film modules will have to compete with those made by other companies that are exploring alternatives to silicon–alternatives that are expected to reduce manufacturing and materials costs even further.