Innovation, Tandem Modules And India’s Solar Future

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The Indian government has developed a comprehensive policy to support domestic solar production, and the country is poised to launch itself into a fast-growing, high-value sector that also supplies the products to meet the country’s massive power requirements. As India looks to carve out a new manufacturing leadership position, it’s most promising path can be forged through the embrace of innovation. These manufacturing innovations are still at the beginning of their learning curve, provide a pathway to overcoming existing efficiency barriers, and avoid the material and energy waste associated with legacy processes. They also provide a strategically competitive alternative to the existing solar supply chain and focus specifically on two steps of the manufacturing ecosystem – wafers and tandem modules.

Harvesting solar energy is akin to farming, and just like the green revolution increased yield per acre in agriculture, it is essential to increase the efficiency of solar panels. Advanced tandem module technology does just that by increasing the energy output of a solar panel by thirty percent. While tandem builds on the manufacturing knowledge gained during the last 30 years, it replaces the basic approach to harvesting sunlight that has defined the solar industry to date with an approach for yielding more power. Existing panels rely on only one light absorber, namely silicon, to convert sunlight to electricity. Indeed, China has built world dominance using this basic “single junction” approach. But this technology is reaching its physical limits and future cost declines or performance gains can only come from solutions that are not constrained by single junction physics. Tandem offers an alternative. It works by combining two semiconductor materials into one solar device, with each material capturing different wavelengths of the light spectrum. Silicon, with its band gap of 1.1 eV, is particularly good at capturing the infrared portion of the spectrum, making it ideal for the bottom layer of a tandem structure. 

However, whether a silicon semiconductor can be used in this way depends on cost. The bottom layer accounts for less than half of the energy produced by the tandem device, so an ultra-low-cost silicon wafer is needed for the total tandem package to prove economically superior. So while tandem represents the future of module technology, silicon wafer manufacturing is the keystone to realizing that future. As India embraces solar manufacturing, it should ensure it is building with the platforms that can deliver this future.

Today, the world’s major wafer manufacturers employ conventional ingot and sawing equipment to produce silicon wafers. During the past decade, China has moved to capture 99% of the world’s wafer production/manufacturing. The scaling achievement, though remarkable, is also inherently flawed as the manufacturing process underpinning the growth is ripe for disruption. The industry relies on a highly-inefficient ingot-based production method. The most significant inefficiencies come from the sawing of the ingot. It is during this process that nearly half of the ingot turns to dust. This dust is referred to as “kerf” and this waste drives the largest loss of energy, as the silicon refining and crystallization process is extremely energy intensive. The more silicon wasted, the larger the carbon footprint and the longer the energy payback.

While incremental improvements, such as diamond wire sawing, and China’s brute force in scaling led to dramatic cost reductions, wafers remain the largest cost driver of industrial solar cell production. Innovation has stalled and standard wafer manufacturing has plateaued, leaving one of the most important industries of the 21 st century tethered to a legacy process with intrinsic inefficiencies. A new alternative has evolved through a decade’s worth of R&D and commercial trials that have resulted in the ability to produce a solar wafer directly from molten silicon in a single-step, entirely eliminating the need for the ingot and sawing. The process heats the silicon to form a molten bath, then freezes a thin sheet of “silicon ice” on the surface and extracts this sheet (wafer) from the molten bath. The same equipment laser trims the sheet to the desired size and adds the trimmings back to the melt. This ability to morph melted silicon directly into a wafer is what gives “Direct Wafer” manufacturing its name. India has a choice its predecessors in crystalline silicon solar manufacturing did not have, to elect innovation such as the Direct Wafer process over generic silicon technology. In doing so, it can achieve the lowest cost of energy today and create the blueprint, through tandem modules powered by Direct Wafer silicon wafers, for global leadership.

Earlier this year, 1366 Technologies (which invented the Direct Wafer process) and Hunt Perovskite Technologies, merged to form CubicPV. The new company’s patented technology achievements, the Direct Wafer process and durable perovskites, enable the leap to tandem solar and will create a solar future defined by high-efficiency and lower embedded energy and materials. Perovskites, though a relatively new solar semiconductor, are the ideal top layer material for a tandem device, exceptional at capturing the visible light of the solar spectrum.

By avoiding the same technology roadmap as its economic rival and with synergistic innovation-led technologies such as those in the CubicPV portfolio, there is no doubt that India can become a center of gravity in solar manufacturing.

By Frank van Mierlo, CEO, CubicPV

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