Solar power research: India is gradually moving towards cleaner and greener energy sources, with several big solar energy projects being inaugurated in the country. However, India only has capacity to indigenously produce about 3 GW of solar cells, and depends heavily on imports to meet its demands, mostly from neighbouring China. However, now, a research team from SSN College of Engineering led by Dean of Research Prof P. Ramasamy, have designed a technology, called Directional Solidification or DS, that could catalyse India’s solar manufacturing abilities.
The research has been published in Material Letters journal and the team has also been given a grant of Rs 12 crore by the Department of Science & Technology (DST) under the Centre.
“The project may lead to new openings in the development of DS process technologies for the growth of high-quality multi-crystalline silicon ingots suitable for the fabrication of solar cells. India has to put more effort in this area,” Prof P Ramaswamy said in an interaction with Financial Express Online’s Bulbul Dhawan, during which he explained more about the research, how it would help India’s solar capabilities and the next step to be taken.
Could you elaborate on what is Directional Solidification (DS) technology?
The majority of photovoltaic (PV) solar cells are fabricated from silicon, which may be either single-crystalline or multi-crystalline. The share of mono- and multi-crystalline silicon (mc-Si) in the market is over 90% currently and it will continue to be so, at least for the foreseeable future. In India, silicon wafers and cells are imported by the solar cell industries, who then convert them into solar modules. Today 98% of the silicon wafers imported into the country are mc-silicon wafers and 2% of wafers are single crystalline wafers. Single-crystalline wafers typically have better material parameters but are also more expensive which are made from Czochralski (Cz) grown ingots.
The Directional solidification (DS) method is emerging as the leading technique for the production of mc-Si. This is because of its improved feedstock tolerance, increased throughput and easier operation. Using controlled cooling, molten silicon solidifies in a single direction which is why the process is called directional solidification. In the recent global market, 450kg to 800 kg commercial directional solidification systems are widely used in production and systems capable of producing 1000kg – 2400 kg ingots are also being developed. The energy consumption is about 8-15 kWh/kg, for DS, whereas for the Cz technique it is considerably higher, in the order of 35kWh/kg.
How will this technology make India self-reliant in solar technology?
By 2030, India’s expected energy import will be 53% of the country’s total energy consumption. So the attention on PV module installation has increased incessantly. India expects to install about 100,000 MW by 2022. At present, from polysilicon to modules, each stage of the supply chain is dominated by firms based in China. Half of the global polysilicon supply is carried out by producers in China.
About 70% of all PV modules installed globally are manufactured by Chinese producers. Necessary efforts are taken by Chinese companies in processing the Silicon chunks, improving the quality of the ingots and efficiency of solar cells. But, in India, no industry is involved in such activities. Most PV module manufacturers are importing silicon solar cells and assembling them into modules. A significant percentage of such imported cells are mc-Si which are grown by the DS process. So it is essential to indigenously design and develop a Directional Solidification System for growing high-performance multi-crystalline silicon ingots.
What are solar wafer and ingot and why are solar wafer and ingot manufacturing abilities important?
Crystalline Silicon Wafers from grown ingots by DS Process are the building blocks for manufacturing solar cells and modules. Indigenous manufacturing capability is indispensable to ensure national energy security.
Apart from China, Japan, Taiwan and South Korea, do any other countries have these manufacturing abilities? What according to you is the reason behind Asian countries being dominant in this technology?
Germany, France, Russia and Brazil have manufacturing abilities apart from China, Japan, Taiwan and South Korea. Many countries have technology that converts raw silica to electronic and solar grade silicon which is used for optoelectronic applications. Due to the economic incentives given by the Chinese government, the majority of the production is centred in China.
Around 90% of poly-silicon (source material for the solar industry) is supplied by China to the global industries and well-established technologies and the research and development labs are available in China, Japan, Taiwan and South Korea. Those are the main reasons behind these countries being dominant in this technology. With the current encouragement given by the Indian Government, India is also likely to join this group of countries in the near future.
Why did the team decide to work on this technology and how did it go about it?
Currently, domestic facilities or industries for producing silicon ingot and wafers do not exist in India. The incessant development of the PV field will increase the requirement of the DS System constantly. I, along with my colleagues, took the initiative to start the research activities on silicon growth 10 years ago at the SSN Research center. MNRE, Government of India approved the project entitled “Development of improved DS process for mc-Si wafers and their application to Solar Cells” with a budget of Rs 5 crore thanks to the support extended by Prof. A.K. Barua. Computation Modelling and Experimental mc-Si growth lab are established well in SSN RC. Several Ph.D. scholars and scientists are currently working in the field of the mc-Si growth process and are publishing good results in international reputed journals. At present, we are the only research group working in the Directional Solidification of multi-crystalline silicon for photovoltaic applications in India.
What is the future course of action that the team is set to take in this regard?
We were awarded the project for “design and development of 800 Kg multi-crystalline silicon mc-Si directional solidification furnace and slicing machines for making commercial size mc-Si wafers” with a budget of Rs 12 crores by Department of Science and Technology (DST), Government of India. The future course of action is to grow mono-like Silicon crystal by DS process. However, Silicon-based module’s lifetime is around 25 years only. So, SSN already initiated the work on recycling end-of-life modules. After successful completion of this project, the whole technology (from growth to wafer making) may be transferred to industries.