As bifacial technology establishes itself among its many proven peers in the world of PV modules, developers are looking into possibilities of added yield from rear-side power output.

In China, PV InfoLink reports that share of bifacial modules has increased from 2% in 2017 to 10% in 2018, driven by the nation’s Top Runner program that offers incentives to include high-efficiency solar technologies.

Last year a report from Bloomberg New Energy Finance anticipated 40% market share for bifacial panels by 2025.

JinkoSolar’s Swan range of bifacial modules include transparent backsheets, setting it apart from its competitors.

The Chinese solar company supplied this interview about the technical aspects of bifacial modules with global vice-president Dany Qian to EcoGeneration.

All leading manufacturers are developing glass-glass bifacial modules, so why is JinkoSolar promoting the use of a transparent backsheet?

Field failure for frameless double-glass modules is not uncommon. Bowing or deformation in frameless, dual-glass modules is occasionally reported, causing the cells to crack and the glass to break. But framed double-glass is too heavy, resulting in substantially higher EPC and O&M costs.

JinkoSolar’s Swan bifacial with transparent backsheet provides a 25%-less weight alternative, resulting in 20% reduction of labour cost. Compared with Swan, conventional double-glass bifacial requires trackers to be stronger and piles to be deeper, which leads to 15% more mount costs and 5% more O&M cost.

Will the bifacial module’s height off the ground lead to higher BOS costs?

If compared with bifacial dual-glass, Swan bifacial with transparent backsheet is proved to reduce BOS costs by about 3%.

Glass-glass modules are known to have off-gassing issues. How does Swan overcome it?

The Swan series using Tedlar PFV film-based backsheet has an acetic acid diffusion rate of 30mg per square metre per day, sufficient to bring the concentration down substantially to prevent corrosion and power loss. This breathable design releases moisture and acetic acid, preventing encapsulant degradation while reducing the risk of delamination and corrosion.

Customers sometimes point out that when you go for the conventional bifacial, the front side becomes less efficient as a 400W panel may step down to 390W, for example. How does Swan overcome it?

The Swan bifacial provides meshed transparent backsheet option, which can increase the second reflection from the gap between cell and cell and can achieve almost the same power as a mono-facial module

Does bifacial require a bit more land than mono-facial, with wider array spacing to allow more light to the back?

Ground-coverage ratio, or GCR, means the distance between arrays. Land cost is one of the key factors in an initial system investment assessment, considering the low irradiance (135W per square metre, defined by TUV Rhein when define module integrity power) absorbed by the rear side. GCR design is much related to the front-side shading consideration.

As to certain project module capacity, when we do the system design, both front and rear side module power shall be considered. Therefore, bifacial module efficiency (total power output) will be higher than mono-facial module, then actually less land is required. If under the same module quantity condition, land area is the same while project yield will be more.