25 - 29 Sept. 2017, RAI Convention & Exhibition Centre, Amsterdam, The Netherlands

04 January 2017

Trends in Solar Module Manufacturing

From the distance, today’s solar module might not look any different than 20 years ago, but researchers and module manufacturers have been pretty innovative on improving the solar module’s contribution to efficiency and yield, often independent from the cell.

The so-called cell-to-module losses (CTM) value is a clear indication of this progress. According to the 7th edition of the International Technology Roadmap for PV (ITRPV), published by the German Engineering Federation’s (VDMA) PV Chapter, the CTM losses for multicrystalline modules would be zero already by 2017, whereas monocrystalline modules would reach this level in 2019. This difference is mainly due to monocrystalline cells featuring already a superior surface texturing that leads to relatively lower reflection losses, but it also means that they benefit less from the ‘coupling gain’ after encapsulation.

Cutting Cells in Two

There are different means to decrease the CTM losses. One is to reduce the interconnection losses and improved light trapping approaches. Interconnection losses can be minimized with ‘half cells’, in which a fully processed cell is deliberately cut into two pieces. The logic behind slicing a full cell in half is that the series resistance losses, which are a square of the flowing current, are reduced to a quarter for half-cut cells compared to a full cell. Norwegian company REC even announced in March 2016, it would switch all production at its Singapore facility to half-cut PERC cells. Several module manufacturers have added such module products to their portfolio as well, for example, Hanwha Q CELLS presented a 315 W mono 60-half cells based prototype module in September 2016.

PhotoRECTwinpeakHalfCellsModule

  Half but powerful: Slicing a full cell in two equal pieces enables to reduce the series resistance losses. Several module manufacturers are offering such modules. Norwegian company REC even announced to switch all production at its Singapore facility to half-cut PERC cells.

Source: REC

Trapping the Light
Another way to improve module performance is to enhance light trapping. The mechanism involves turning the barren areas of the module into passive energy generation sites. The portion of light that hits the non-active area of the module - such as ribbons and gaps between cells - are reflected back into the ambiance, thus they go to waste. However, employing special materials such as grooved or coated ribbons and reflective backsheets pushes back sunlight onto the active PV area by means of total internal reflection.

Nearly every backsheet supplier is supplying reflective backsheets today. Germany’s Schlenk and US-based Ulbrich, for example, have been supplying silver grooved solar ribbons, while Finnish company Luvata and Bruker-Spaleck from Germany are offering colored ribbons.

At the 32nd EU PVSEC conference in 2016 in Munich, Fraunhofer ISE presented another innovative ribbon design, called TriCon-Concept, which has a triangular cross section. The researchers found that in an elevation tracked module using TriCon 2.32% more light reaches the cell surface over the year compared to rectangular interconnectors in a 5-busbar configuration; the improvement was 2.02% over round wires.
 
More or ‘Multi’ Busbars
All module manufacturers have been increasing the number of busbars - and there’s no end in sight. The bulk of the industry already has or is adapting their processes to 4-busbar configuration, while some module makers have been already started moving towards 5-busbars, such as SolarWorld.

This approach is more beneficial at the cell level - because increasing the number of busbars significantly reduces internal electrical resistance as current carried by fingers reduces with increase in busbar count. But the major implications are on module manufacturing. At some point you need to change the string soldering machine. The leading stringing and tabbing equipment makers are now offering 4 and 5 busbars as a standard feature for their tools. For some earlier 3-busbar models also field upgrade packages are available.

Going beyond 5-busbars is still a topic of discussion, especially if it makes economic sense. An alternative are ‘multi-busbar’ solutions, where the typical flat solar ribbons are replaced with more than 10 round copper wires for realizing the series connection. Meyer Burger from Switzerland and Germany’s Schmid are offering such multi-busbar based interconnection production equipment.

Glass-Glass & Bifacial   
Another important change the PV industry seriously working on at the module level is replacing polymer backsheets with glass. These glass-glass modules enable to take the complete benefit of bifacial cells, which are light sensitive on both sides. Germany’s SolarWorld, for example, is offering bifacial glass-glass designs for their Bisun modules, which come with 5 busbars and are based on monocrystalline PERC technology.

PhotoSolarWorldGlass GlassModule   Very advanced standard silicon module: German module manufacturer SolarWorld offers glass-glass panels with bifacial cells and 5 busbars, based on monocrystalline PERC technology. The photo shows the module from the front and back.

Source: SolarWorld

Bifacial technology enables further innovations. At EU PVSEC 2016, a research group from the Institute for Solar Energy Research Hameln (ISFH) presented a new interconnection process called “flip-flop” for bifacial cells. Here, instead of interconnections routed from the front of one cell to the rear of an adjacent cell, the cells are placed with alternate orientation, while the interconnection wire runs straight in front-to-front and rear-to-rear fashion. According to ISFH, the approach has the potential to increase the module efficiency by 0.5% absolute on aperture area.

Choosing the Right Platform
These are just a few trends we see in module manufacturing, but there is so much to explore to improve the technology. With all these technical developments requiring a strong cooperation between researchers, equipment makers, material vendors and PV manufacturers, the upcoming 33rd European PV Solar Energy Conference & Exhibition (EU PVSEC) in September in Amsterdam offers the perfect platform to present your innovative solutions for solar module making and beyond.
Reserve your booth by 15 January 2017 to profit from a 10% early bird discount.