While silicon substrates with 156mm side length have been a standard in solar wafer manufacturing for more than a decade, manufacturers have been able to increase the side length, though marginally to 156.75mm around a decade ago. This size is called M2 and offers an area gain of 2.25% over wafers with 156mm side length.
The size of a monocrystalline wafer is increased with increasing diameter of the cylindrical ingot and through optimization of pseudo edges in the cutting process (meaning as little as possible is taken away from the corners to make it pseudo square). In case of multicrystalline wafers the change is more straightforward. Since multi wafers are fully square in shape (the crystal ingot is also square), increasing the side length from 156mm to 156.75mm means more or less to simply cut out a larger block from the large square ingot. This accounts to close to 1% gain in surface area.
The world's largest wafer manufacturer LONGi Group, which produces exclusively mono wafers, commercialized the M2 format in 2017, and commercial modules based on this wafer size are available since then. M2 became sort of an unofficial standard in 2018 with a market share of around 90%. The main advantage of switching from M0 to M2 is it does not require any major re-adaptation in the production process further downstream. The gains in area and the corresponding power win were more or less for free.
Already at that time, a few vertically integrated module manufacturers began exploring possibilities to increase wafer sizes beyond M2. JinkoSolar was on the forefront and started offering module products based on 158.75 mm wafer size, which is a full square silicon slice and referred to as G1. Following the lead of JinkoSolar, JA Solar and Trina Solar also adapted to G1 size in the first half of 2019. Prior to this, already in 2017, LG introduced an even larger wafer format of 161.75 mm, known as M4.
Canadian Solar was the first to take an even larger jump in 2018. The company, which was focusing mainly on multi technology at that time, introduced multicrystalline panels with M6 wafer formats of 166 mm side length. This was a strategy to overcome multicrystalline silicon technology's lower cell efficiencies.
No wonder the largest monocrystalline wafer supplier LONGi took over Canadian Solar's initiative and introduced M6 monocrystalline silicon wafer products in the first half of 2019. Such M6 wafers have about 12% higher surface area compared to the M2 format.
Though only for a short time, it appeared like M6 was the largest wafer size and would remain so for some time. However, less than 3 months later, the other leading Chinese mono ingot/wafer manufacturer Tianjin Zhonghuan Semiconductor (TZS) announced in August 2019 to introduce a M12 wafer product – with side length of 210 mm, called M12. Since these wafers have a full square shape, the industry colloquially refers to them as G12.
However, leading vertically integrated module producers, such as JinkoSolar, JA Solar, LONGi Solar and Canadian Solar with significant in-house wafer capacities would need some time to adapt to 210 mm (if they want to). For now, most of them are focusing on 182 mm wafer size (M10), which enables module designs with power ratings beyond 500 W as well. However, today's market is flooded with a wide variety of wafer sizes, probably more than ever before – M2, G1, M4, M6, M10, G12. The main motive behind the increasing the wafer size is to increase the module power.
For detailed information on Larger wafers and Module size see TaiyangNews report on 500W+ Solar Modules, which can be downloaded for free.
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