Which is the best size of PV cell ?
These years, photovoltaic technology has been developing rapidly. For PV-cell, High-efficiency PERC, double-side cells, black silicon and other technologies have been put into mass production. N-type and heterojunction technologies have begun to have a certain market share; For PV-module, the technologies such as Double-Glass, Half-Cut, Multi-Busbar (MBB) and the shingled have also entered the stage of large-scale industrialization. In addition, in terms of monocrystalline silicon wafers, it has not only some great technological breakthroughs in the process of crystal pulling, slicing, but also the size has a tendency to become larger.
Before 2010, monocrystalline silicon wafers were mainly made up of small-sized silicon wafers with a margin of 125 mm（Ingot diameterØ164mm）and just a small number of wafers with a margin of 156mm (Ingot diameter Ø200mm). After 2010, The proportion of 156mm wafers is getting bigger and bigger, and has become the mainstream of PV industry. The 125mm P-type silicon wafer was almost eliminated around 2014, and just only applied to some modules of IBC cell and HIT cell. At the end of 2013, five companies, Longi, ZHONGHUAN, Jinglong, Solargiga and Comtec, jointly released M1 (156.75-Ø205mm) and M2 (156.75-Ø210mm) wafer standards. M2 has increased the power of the module by more than 5Wp by increasing the silicon area (2.2%) without changing the size of module. Therefore, M2 quickly becomes the mainstream of the industry and maintains for several years. During the period, a small number of M4 size (161.7-Ø211mm) wafers came into the market, which is 5.7% bigger than M2, and the products were mainly N-type double-side modules.
Here an analysis was made to explain why the silicon size is getting bigger and bigger.
1. In terms of production, the production rate of the cell and module in the form of piece/hour is basically fixed. To increase the size of wafer can increase the power of the cell and module produced per hour.
As a result, the cost of the equipment, labor, and even the company per Wp is reduced, thereby reducing the manufacturing cost of the cells and modules, which is especially noticeable when the 125mm silicon wafer is switched to 156mm silicon wafer.
2. In terms of the cost of PV power station, a ground power station is taken as an example, the higher power modules obtained by increasing the size of wafer in the series with the same amount increase the efficiency of the series. Correspondingly, the cost per Wp of the brackets and pile foundations will be reduced; As the effect of large module to personnel carrying and installation speed can be eliminated, the installation efficiency per Wp of module and brackets increases; The capacity of the array can be regarded as fixed by the inverter, so that the high power module could reduce the amount of the combiner box or the string inverter, and the bracket amount, which could reduce the covered land of each array (considering the spacing between the front and rear brackets, the left and right brackets), At the same time, the reduction of the bracket and the covered land would reduce the amount of cable used.
According to the relevant calculations, the 425Wp module using 166mm wafer will save the BOS cost of at least 5 cents/Wp compared to the 380Wp module using M2 wafer (both 72 cells), if using tracking bracket or in west countries of high labor cost, the saving of BOS cost would be further increased.
According to the above two points, the size of the silicon wafer should be as large as possible under the premise of production equipment and personnel carrying, in order to obtain more savings of solar module costs and system BOS cost.
For the crystalline silicon module, it is possible to adjust the current size to a more cost-effective size by means of the opportunity of this industry change, which could be stable for many years, like the adjustment of 125mm to 156mm.