Breakthrough for solar energy

Today, about 70% of the energy is wasted when the rays of the sun is being converted into electric power for household consumption. This waste is a major problem for solar power as a renewable form of energy, but now a more efficient technique may be on the way. The solution is based on research done by professor Sergey I. Bozhevolnyi and his research team, as can be read in the latest issue of the international journal Nature Communications.

The new technique, based on nano-optics, introduces a way in which metals can be used to convert light into electric power at an extremely low rate of loss.

Solution: Black metal with nano-focusing
The research team has found a new approach to converting shining metals such as gold, silver and platinum into black metal by changing the nano-structure of the surface. When the metal is 'black' it means that most of the light that hits the surface is being absorbed by the metal, by which the light is converted into heat.

Until now it has only been possible to obtain this effect (black metal) by destroying the surface of the metal with intense laser light, thus generating soot and other random particles. Earlier systematic solutions have only had absorption within a very narrow wawelength spectrum, entailing a lot of waste of energy. 

”Our approach is also conceptually new because we work with 'nano-focusing' of the light. It is a method which has only been known for the past 10 years. It means that the light is constantly being pressed into a narrow metal groove until it stops and is absorped. This focusing makes the absorption of light extremely efficient, so that about 96% is absorped over a wide wawelength spectrum," says Sergey I. Bozhevolnyi.

Technique reduces waste
The method can be employed in various contexts, but the professor sees a great potential within thermophotovoltaics, which is about converting heat into electric power via light (fotons), as for example when solar energy is made into electric power. 
In general, the emission of light by various heated materials will, with respect to colour, be the same as their absorption spectrum. This means that if the surface only absorps blue light, it will in principle also only be able to emit blue light when the material is heated.

”Our black metal will highly increase the efficiency of the heat that is generated by the energy conversion, by which we get more electric power. The technique can therefore be employed in compact, energy saving electric generators without any moving parts," he explains and continues: 

”The method may turn out to be a far better way to convert solar energy into electric power, compared to what we do today. There are clear signs indicating that conventional solar cells are less efficient than the type of generators on which we are working. If we optimize the method, the waste problem in solar energy can be solved," he says, pointing out that there is also a principal upper limit to the efficiency of conventional solar cells.  

Cheaper solution is next step
Nature Communications is being carefully scrutinized by scientists from all over the world, and therefore the publication of the results will play a crucial role in the future:

”Our conclusions will stimulate other scientists working within the same field to further develop our concept," says Sergey I. Bozhevolnyi.

“The next step is to examine cheaper metals, so that we can continue working towards a solution that is practically applicable. We will also try to find more economical and production-friendly methods for fabricating these surface structures."  

The article ‘Plasmonic black gold by adiabatic nanofocussing and absorption of light in ultra-sharp convex grooves’ has been published in the latest issue of Nature Communications.

For more information, please contact
Professor Sergey I. Bozhevolnyi, The Institute of Technology and Innovation, tlf. 6550 7341 / mob: 20585128 / seib@iti.sdu.dk