Vacuum receivers are used in parabolic troughs for concentrated solar power applications like solar power plants. They have a substantial influence on the power plant’s efficiency, as they convert solar radiation into heat. Inside of the absorber tube is a steel core which must be capable of absorbing large quantities of solar radiation without emitting a significant amount of heat. To this end, the steel core is covered with highly transparent coated borosilicate glass. But prolonged exposure to solar radiation damages the coating, and over time, they will cease to adhere to the glass envelope, allowing temperature fluctuations to affect the tube’s performance.
Creating Technology, Creating Processes
To address this problem, Schott Solar turned to the Fraunhofer Society, whose broad expertise in solar thermal absorptive coatings and sputtering processes could complement Schott's own manufacturing experience to create a new, more durable vacuum receiver. Based on Schott's specifications, Fraunhofer scientists were able to develop a unique anti-reflective coating, one that resisted abrasion for longer periods of time than current marketed alternatives. In addition to having a longer life span than competing receivers, the new technology was also more efficient, offering an absorption rate of 95%. Even at temperatures of more than 400°C, no more than 14% of the total heat was left unabsorbed.
Beyond developing the required coating, Fraunhofer also pioneered the new manufacturing process needed to produce the receivers themselves. The first industrial prototypes were produced on Fraunhofer's own pilot lines; thereafter, Fraunhofer engineers assisted in selecting and installing, calibrating and running the necessary equipment in Schott Solar's new production environment.
Setting a New Standard
Today, the new receiver tubes have set a global standard, enjoying a competitor-crushing 80% market share in a rapidly growing strategic market segment. Schott Solar, who now own the patent for the coatings, are expected to dominate this $600M market in the short- and medium term. The vacuum receiver itself is manufactured at a dedicated facility in Albuquerque, New Mexico.