Ultra-black nanoneedles set new standards for light absorption in solar towers
Concentrated solar energy is gaining ground as a future renewable energy source thanks to the efficient storage of thermal energy. Historically more expensive and complex than photovoltaic systems, advances have made concentrated solar energy increasingly viable and adopted for renewable energy production.
Inigo Gonzalez de Arrieta from the Thermophysical Properties of Materials group at the University of the Basque Country (EHU) described their work on ultra-black materials for tower applications. “We are investigating ultra-black materials for use in solar towers.” In these plants, mirrors focus sunlight on an absorber tower.
“The more we can achieve by absorbing materials that are more effective, the more competitive the systems will be, and we will create opportunities for this type of energy,” said Gonzalez de Arrieta. EHU uses the most modern equipment for thermo-optical analysis of samples, while few laboratories worldwide are equipped for such research at high temperatures.
The team characterized copper cobaltate nanoneedles, patented by UC San Diego, and found marked improvements over previous absorber technologies. “We saw that these copper cobaltate nanoneedles outperformed the carbon nanotubes used to date, and that these nanoneedles performed even better when coated with zinc oxide,” said Gonzalez de Arrieta.
Solar tower designs strive for maximum light absorption by using ultra-black materials. Vertically aligned carbon nanotubes, the blackest available, have strong light-catching ability but lack stability at high temperatures and humidity, requiring additional coatings that reduce efficiency. “Carbon nanotubes absorb about 99% of light, but they cannot be used on solar towers.” In contrast, copper cobaltate nanoneedles – especially zinc oxide coated – showed improved thermal stability and absorption of up to 99.5%. Today’s standard black silicon absorbs approximately 95%.
Dr. Renkun Chen (UC San Diego) and collaborators at the U.S. Department of Energy aim to deploy zinc oxide-coated copper cobaltate nanoneedles in solar towers, although the development faces regulatory and technical challenges.
Solar tower facilities operate in areas such as Andalusia and desert areas around the world. Concentrated solar power plants supply approximately 5% of Spain’s energy, providing clean generation and effective thermal storage. The heat is used to melt special salts, retaining molten salt for efficient delivery of the electricity grid, even after sunset.
EHU continues to develop new coatings to further improve the optical and conductive properties of the next generation of solar tower absorbers.
Research report:AZO-coated refractory nanoneedles as ultra-black wide-angle solar absorbers
