Sand to Systems

A comprehensive take on solar cell design, manufacturing and applications

In view of the rapid changes happening in the manufacturing process, it is crucial for solar cells and modules to adapt to new developments. To detail the developments in the solar manufacturing space, Rabindra Satpathy, board member of the International Solar Energy Society, and Venkateswarlu Pamuru, chief technology officer, Grand Solar Private Limited, have authored a book, Solar PV Power: Design, Manufacturing and Applications from Sand to Systems. The book includes information on system design and the entire value chain of solar PV manufacturing. Renewable Watch presents a review of the book written by Goutam Samanta, head, PV technology, Juniper Green Energy Private Limited…

The book has covered the following contents in its 10 chapters: manufacturing of polysilicon; silicon crystal growth process; silicon wafer manufacturing process; manufacturing of crystalline silicon solar cells; manufacturing of crystalline silicon solar PV modules; solar PV systems and applications; off-grid solar PV systems; rooftop and BIPV solar PV systems; grid-connected solar PV systems; and grid integration and performance and maintenance of solar PV systems. The authors have covered the comprehensive manufacturing process steps, in-line quality check points of silicon-based PV products right from sand to polysilicon, ingots, wafers, and solar cells and modules, as well as specifications and bill of materials required at different stages. The book has also described the need for silicon-based module reliability testing to measure the performance of panels even after 25 years of system operation. The system design has also covered an in-depth design of complete solar PV systems and applications on off-grid, rooftop, BIPV ground mounted and floating solar systems.

The book describes in detail solar PV systems including water pumping systems, home lighting systems, refrigeration, telecommunications, oil and gas platforms, cathodic protection, microgrids, hybrid power and transport highways. It has also given a detailed description of the design and construction of ground-mounted grid-tied PV systems with balance of systems; civil works of foundations and structures with fixed tilt tracker systems and bifacial modules; and electrical components, including their specifications, integration and energy storage application. Finally, the book has covered a few critical parameters for the performance of power plants for delivering the expected power as per design. It has also covered the operations and maintenance (O&M) requirements of power plants to achieve the desired LCoE.

I have been working for more than 28 years in international PV industries, and overall 35 years in electronics industries, and I have not seen any single book that covers such a wide range of topics, including manufacturing processes, design and construction of PV power plants and O&M. I strongly believe that this book will be very useful for all students, teachers and professional practising engineers in the field of solar PV.

“Solar modules will see a decline in cost”

Interview with Rabindra Satpathy, Board Member, International Solar Energy Society

What was the major idea or philosophy behind writing this book? 

Being passionate about solar energy and having worked for more than 30 years in India and the Asia-Pacific solar PV industry, I wanted to write down my theory and practical learnings in the solar PV value chain, including design, manufacturing and various applications. This book is meant for practising technicians, engineers and entrepreneurs to harness solar power to mitigate and combat climate change, very much aligned to Atmanirbhar Bharat. It aims to create a new brand of solar technicians, designers, engineers and researchers.

How has the solar power segment evolved over the past decade? What have been the key positives and negatives?

During 1984-85, while designing a 25 kWp solar PV-diesel hybrid power plant for a forest lodge in Lulung, Odisha, or planning and designing the installation of a 1.1 MWp wind power plant at Puri, Odisha, I used to believe that the power segment will embrace renewables as a supportive power, not as mainstay power. Come 2010, with the 20 GWp National Solar Mission and 1-plus GWp solar power park in Gujarat, solar power deployment started gaining momentum and has now scaled to achieve more than 34 GWp of capacity, up from 2.6 GWp, in the past 5.5 years.

What are the key trends in PV technology? Which technologies are expected to gain traction in the near future?

Polysilicon is the raw material required as part of the supply chain in solar cell production. Siemens’ process is the dominant technology in polysilicon production. The FBR process and union carbide processes are not able to compete with Siemens’ process. The crystal growth method needs to meet the requirements of solar PV ingot, or wafer, or cell manufacturers to achieve high yield and enhance their performance.

On the wafer manufacturing front, the slurry-based wafer technology completely shifted to diamond wire saw (DWS) in 2018 for mono and multicrystalline silicon wafers. With the introduction of passivated emitter rear contact (PERC) technology in solar cell production, p-type wafers dominated the market. The casted multicrystalline Si technology is no longer dominant; its share shrank to less than 40 per cent in 2019. The market share of monocrystalline wafers, including p and n type, was 60 per cent in 2019. The n-type wafer utilisation has increased with the introduction of heterojunction (HJT) and TopCon-based solar cells. The thickness of the wafer is reduced with the usage of DWS in cutting the wafers.

Back surface field (BSF) technology with monocrystalline and multicrystalline wafers has dominated the solar industry for more than a decade. To mitigate the limitations of BSF technology, the researchers adapted PERC as a promising technology for industrial solar cell production. The main aspect of PERC technology is incorporating a rear-side passivation scheme into a standard BSF cell technology. This concept deals only with the optimisation of the rear surface, aimed at reducing recombination losses on the dark side of the cell, and it is fully independent of the front side.

The steps required to shift from PERC to a bifacial cell are negligible as compared to the modifications needed to upgrade from standard BSF to PERC. So, more manufacturers are opting for PERC-based bifacial technology. In 2019, mono-PERC dominated the industry. n-type mono wafer-based technologies like inter-digitated back contact and HJT are gaining traction, contributing a market share of 10 per cent. At present, mono PERC-based monofacial and bifacial solar cells with sizes of 166 mm, 182 mm and 210 mm are dominating.

Advanced solar PV module technologies such as bifacial modules, shingled-cell modules, half-cell modules, and multi-busbar modules work with high efficiency solar cell technology to improve the reliability of the PV system, increase power generation and minimise the LCOE.

There have been many advancements in solar module technology, including half-cut solar cell-based modules, monocrystalline PERC solar modules, bifacial solar modules, solar modules with multi-number busbars comprising 9-12 wires, higher wattage modules with half-cut or triple-cut mono PERC solar cells in different sizes, HJT solar cell-based modules, shingling-based solar modules. Module wattages are increasing up to 600 Wp. With the advent of bifacial solar modules, the horizontal single-axis trackers are coming into the picture to generate more energy for large-sized solar PV power plants.

What is your perspective on the evolution of module prices over the years? How do you expect prices to change over the long term?

Given the increase in solar cell efficiency and the adoption of both p- and n-type solar cells that use thinner wafers, and new global solar PV installations expected to increase 27 per cent to reach 181 GWp in 2021, the price of solar PV modules is declining.

As per the latest reports, solar PV modules will see a decline in cost over the next one to two years due to high wattage module production and 27 per cent increased global demand in the current year.

What are the major interventions needed to increase the scale of domestic manufacturing across the entire PV value chain?

In my view, the major interventions needed in the solar PV value chain are a new module design and new solar cell manufacturing process to reduce the cost of solar PV modules (Rs per Wp). It also calls for new wafer technology such as direct wafering over the current DWS cutting and the adoption of a cost efficient polysilicon manufacturing process.

India’s solar PV manufacturing industry and solar entrepreneurs are in fast-track mode to transition to new technology-based solar PV value chain manufacturing. We are not carrying an old baggage of technologies and can adapt to the latest viable technology options to achieve global cost competitiveness. The current Aatmanirbhar Bharat initiative, combined with the production-linked incentive scheme and incentives for solar value chain research and development, will enhance capacity addition and make India-based solar companies cost competitive around the globe.

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