New material developed to tap solar power for thermal energy

Vijay Mohan 

Chandigarh, November 11 

Indian scientists have developed a new material that has demonstrated the highest efficiency of converting solar power to heat energy amongst all such materials available so far. 

The material with unique marigold-like carbon nano-structures has immense potential for high-altitude areas like Ladakh and Himachal Pradesh where abundant sunshine is available most time of the year and, besides transforming the solar-thermal energy market in India, is a step in the direction of net zero carbon emission. 

For most part of history, fossil fuels have served human thermal energy requirements with adverse effects on environment and biodiversity and increasing greenhouse gas emissions. Though recently light directly from the sun is being harnessed and converted into thermal energy, only a miniscule percentage of the total heat energy the sun radiates has been utilized, according to the Ministry of Science and Technology. 

The new material designed at the Indian Institute of Technology (IIT) has made a breakthrough in the amount of heat that can be absorbed and stored. Called nanostructured hard-carbon florets (NCF), the material has shown solar-thermal conversion efficiency of 87 percent, which is the highest so far, the Ministry has claimed. 

It absorbs more than 97 percent of the ultraviolet, visible and infrared components of sunlight and converts this into thermal energy that can be effectively transferred to either air or water for practical applications.  

Researchers demonstrated that NCFs heats the air from the normal prevailing temperature to 60 degrees Celsius and can thereby provide smoke-free space-heating solutions. “This is particularly relevant for heating spaces located in cold climatic conditions that receive abundant sunshine such as Leh and Ladakh,” said Prof C. Subramaniam from IIT said. 

Solar thermal convertors, like those present in solar water heaters, are already in use in many places around the world, but most of them are expensive, bulky and potentially harmful to the environment.  

“Conventional coatings and materials for solar-thermal conversion are based on chromium or nickel films. While anodised chromium is a heavy metal and toxic to the environment, both chromium and nickel films exhibit solar-thermal conversion efficiencies ranging between 60-70 percent,” Dr Ananya Sah, the lead author of the study, said. NCFs, on the other hand, are made primarily of carbon and are inexpensive to produce, environment-friendly and easy to use, she added. 

Apart from its remarkable efficiency of converting sunlight into heat, another advantage of NCFs lies in their processability. The materials to develop them are readily available and the technique is easily scalable, making large-scale manufacturing commercially inexpensive. Once manufactured, NCFs can be spray-painted onto almost any surface, similar to powder coating a surface, reducing the cost of application and maintenance.   

In addition, the researchers demonstrated that hollow copper tubes coated with NCFs can heat air circulated through them to over 70 degrees Celsius. They also presented their ability to convert water into vapour for purification with an efficiency of 186 per cent, which is the highest ever recorded.