Spanish scientists have created a material that swallows 99.5% of light. And it is great news for renewables

At first glance they look like invisible needles, thin to the extreme and tiny like a thousandth of a human hair. A group of Spanish researchers has created ultra-black nanoneedles that absorb up to 99.5% of the solar radiation they receive, a record figure that not only sets an optical record, but will increase the efficiency of solar thermal plants.

Made in Euskadi. The discovery comes from the Thermophysical Properties of Materials group at the University of the Basque Country (UPV/EHU). There, the researchers have designed a surface composed of copper cobaltate nanoneedles—a mixed oxide of copper and cobalt—with exceptional optical properties. Its ultra-black tone and its resistance to humidity and high temperatures make it ideal for solar tower receivers.

According to tests, the material achieves an absorption of 99.5% of sunlight, surpassing black silicon (95%) and carbon nanotubes (99%). “We are looking for ultra-black materials for more efficient solar towers,” noted researcher Íñigo González de Arrieta.

A change for solar energy. In concentrating solar thermal power plants (CSP), hundreds of mirrors reflect and concentrate sunlight towards a central tower. There, heat is used to melt salts that retain thermal energy and allow electricity to be generated even when the sun has already set.
The key is to take advantage of each photon: if the receiver material reflects part of the light, that energy is lost. And this is where the new nanoneedles come into play.

Until now, the most used material was black silicon, with an absorption level of 95%. The new nanoneedles, on the other hand, could raise that figure significantly and, with it, make solar thermal energy, one of the most promising clean sources in countries like Spain, more competitive and profitable.

Beyond the blackest black. Carbon nanotubes seemed unbeatable: dark as a vacuum, capable of trapping almost all light. But they had an invisible enemy: the heat and humidity deteriorated them quickly.

The copper cobaltate nanoneedles, developed by the Basque team, endure what their predecessors could not. They withstand temperatures above 700 degrees without losing effectiveness and, in addition, they are more stable. In solar towers, that difference can translate into more energy and less maintenance.

A real impact. Dr. Renkun Chen, from the University of California, San Diego, is collaborating with the Basque team and the United States Department of Energy to study the feasibility of applying nanoneedles to industrial solar plants. “We observed that these nanoneedles performed better than the carbon nanotubes used until now, and that their performance increased when coated with zinc oxide,” Chen explained..

However, González de Arrieta himself clarifies that there is still some way to go: the next pilot-scale tests will determine if the process is economically viable and if the material can be produced industrially without losing its optical properties.

Darker, brighter. Ultrablack nanoneedles are an example of how nanotechnology applied to energy can have a direct impact on global sustainability. The UPV/EHU team plans to continue developing new compounds with better thermal and optical conductivity, designed to withstand the challenges of future solar towers.

Promoting this renewable energy offers many advantages: it is totally clean and can also be used when the sun does not shine,” recalled González de Arrieta. And if everything goes as expected, the future of solar energy could be, paradoxically, darker than ever.

Image | Flickr

Xataka | In the midst of a trade war, there is a battle that China has already won: that the world depends on its new energy