Last Word: Bifacial Plus Tracking Boosts Solar Energy Yield by 27 Percent

By Hongbin Fang, LONGi Solar

While U.S. solar developers may be worried about the Section 201 tariffs another trend could help offset their impact: high-efficiency modules. 

In particular, monocrystalline and bifacial modules that use passivated emitter and rear cell (PERC) technology have demonstrated the potential to increase energy yields, potentially enough to erase the price hike inflicted by the tariffs. 

PERC cell capacity has risen from just a few pilot lines five years ago to more than 35 gigawatts in 2017, or nearly one-third of total global cell capacity. This large ramp-up in capacity has been driven in part by policy. China’s Top Runner Program was designed to encourage the production and installation of high-efficiency solar equipment. The most recent round of the Top Runner Program required monocrystalline cells and modules have efficiencies of 21 percent and 18 percent, respectively.

Bifacial PERC modules – which produce energy from the rear side of the module as well as the front – also widen the energy production gap with traditional multi modules. 

LONGi recently conducted field tests to compare the energy yield of bifacial, mono, and multi modules installed in China. In one test, two roughly 18-kW fixed-tilt installations were monitored for three months and the bifacial modules outperformed the other with a more than 11 percent higher energy yield. 

The difference was even starker comparing a 336-kW system using bifacial modules and a tracker with a similar size system using multi modules and no tracker with the bifacial + tracker system yielding 27 percent more energy. Even when both systems had a tracker, the bifacial system outperformed the multi modules by 14.3 percent. 

Further, the price difference between mono and multi has narrowed dramatically in recent years. What was once as much as a $0.40 per piece price difference between multi and mono wafers in 2012 is now in the $0.10 to $0.15 range, which means that PERC modules have achieved cost parity with multi. 

A $0.10 to $0.15 difference translates into a $0.02 to $0.03 per watt difference on wafer cost. But that $0.02 to $0.03 has already been more than offset by the high efficiency on the cell and module level, so mono PERC module is cost competitive comparing to multi module.

My company has a helped drives these cost declines and efficiency improvement by investing 5-7 percent of revenue into R&D each year, last year investing ~$170M in the development of mono ingot, wafer, cell and module technology, more than previous top spenders First Solar and Sunpower. 

We believe we will be able to achieve mono wafer non-Si cost at 1 RMB (~$0.16) per piece by 2020. Even in the three short years that we have been in the cell and module business, we’ve improved cell efficiency by 1.5 percent (absolute) last year and demonstrated a p-type mono PERC cell with 23.6 percent efficiency this year. 


Hongbin Fang is director of technical marketing for LONGi Solar.


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