SMART nano coating for solar cells

The solar power market has been witnessing several innovations even as it rapidly approaches maturity. One such innovation is a nano coating introduced by Dr Aldrin Antony, a National Solar Science Fellow of the Ministry of New and Renewable Energy (MNRE), in July 2017. Antony is leading the research group to fabricate Silicon Heterojunction solar cells at IIT Bombay, along with Anish Kumar Soman, a senior research fellow in his project and a Ph.D. student at the University of Delaware, USA.

The team has taken a new step in conventional solar technology with coloured solar cells that can be integrated into buildings, in window glass, facades and roof shingles, making them an attractive choice for the urban landscape. The technology allows colour coating of solar glass buildings without affecting the energy-harvesting property of the panels. This has been done using a nanophotonic coating called selectively modulated aesthetic reflector technology (SMART).

So far, conventional technologies have required the placement of solar panels on horizontal surfaces like rooftops, and the panels are typically limited to blue and black colours, as these absorb more light. Other colours reflect more light, permitting less of it to reach the solar cells. This makes them less popular with designers and architects. However, the SMART coating, as it is called, reflects only a selected wavelength of light, which gives it a coloured effect, while allowing the cell below to work with 70-80 per cent relative efficiency for colours like red, green and blue and maintaining a minimum of 60 per cent for white. These values can be improved slightly by using better transmitting glass in the modules. SMART coating modules can also be used on vertical areas of buildings, increasing the options for designers to integrate them into their projects and, at the same time, increasing the total surface area installed.

Research on the technology was facilitated by the National Centre for Photovoltaics Research and Education at IIT Bombay and was funded by the MNRE under its AMANSI project. AMANSI is an initiative by the ministry targeted at developing indigenous equipment and processes to achieve high efficiency solar cells. Although the development of SMART coating was not a direct deliverable of the project, the research was done out of scientific curiosity. Conceding that the coatings may not be able to achieve mass use as they are expensive, they may be a good option for people who value aesthetics over economy. It is also possible that if it is mass produced, the cost of the SMART-coated glass would be almost comparable to that of architectural glass.

The single biggest challenge, as discussed by Antony, has been to make white solar cells. White reflects the highest amount of light among all colours. However, given the team’s expert knowledge of photonics and material science, it was able to maintain a relative efficiency of 60 per cent for the white panels.

The inventors filed for an Indian patent for the technology in 2015 and a Patent Cooperation Treaty application in 2017. To make the technology commercially viable and set up production units, they have approached the government for financial aid. The team is reportedly looking for local players instead of international ones to promote technology development within the country and contribute to the government’s Make in India initiative.

As time progresses, along with high efficiency and low-cost solar cells, it is also important to give consumers options to customise technology as per their requirements as well as lay greater emphasis on aesthetics.

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