Bifacial technology lifts solar power to the next level. Instead of hiding the back side of solar cells with an opaque polymer sheet to protect them from diffused and reflected light, the rear is now also open for sunlight absorption. Actually, the change starts at the cell level. There is little effort to turn an advanced cell architecture into a bifacial solar.
Like many advanced cell concepts, bifacial is not new. But the time for bifacial PV has come only now. Recently, PV manufacturers have increased the focus on improving efficiency with advanced cell architectures and module makers were interested in glass-glass module configurations. The move in particular towards mass production of PERC and other advanced cell technologies and transparent backside products is now enabling solar's evolution to bifacial technology.
The choice at the cell level to go bifacial is mainly between PERC, PERT and heterojunction (HJT). However, PERC is clearly predominant, because it is now so wide spread and almost has become a standard in today's p-type monocrystalline segment. Moving from PERC to bifacial technology is not only easy, but also almost free for manufacturers as basically no additional cost is involved to turn a monofacial PERC cell into a PERC bifacial cell (it only requires to change the rear contact grid). But PERC comes with a caveat – and that is a lower bifaciality of 70 to 80%. On the other hand, PERT and HJT, which are based on n-type and intrinsically bifacial in nature, have higher bifaciality of up to 90% and above 90%.
At the module level, the major change required to go bifacial is to make the rear cover transparent. This can be done by using glass or transparent backsheet. While glass is the current state of the art, backsheet suppliers are working hard to push transparent backsheets, promoting low weight and several other advantages, which are the reasons why glass-backsheet configurations dominate over glass-glass today. However, several module manufacturers offer 30-year performance warranties for double glass modules, something that backsheet-based products have not reached so far.
Bifacial is not a prototype concept, several leading module makers are offering bifacial modules commercially based on different technologies and different configurations. Like with standard modules, bifacial panels are available typically in 60 and 72 cell configurations. Some module makers have already adapted advanced module concepts, such as half cut cells, to bifacial technology. Such products are already offered commercially.
This survey includes two Q&As about the latest on bifacial technology from different viewpoints – one with leading vertically integrated mono PERC module manufacturer LONGi, another with leading backsheet component supplier DuPont.
Bifacial Solar Module Technology 2018 Report in detail:
After an introduction (1) and overview on basics, history and recent developments in bifacial solar (2), we provide details on the different bifacial cell technologies (p-type and n-type) (3). We also look at the different components needed for bifacial modules (glass-glass vs. transparent backhsheets, standardization, etc.) (4), provide examples on system performance (5) as well as overviews on demand forecasts (6) and cost comparisons (7). Following the conclusions (8), we include two Q&As discussing the latest bifacial solar developments with LONGi and DuPont (9).
You can download the TaiyangNews Bifacial Solar Module Technology Report 2018 for free here.