Sponsored Content: LONGi Solar - An Installer's Guide to Bifacial Modules
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The solar industry has entered a new era, one of high-yield solar modules, improved system performance and a more competitive levelized cost of electricity (LCOE). Installers and developers are embracing best practices in module manufacturing and increasingly seeking modules with higher energy yield because of the advanced technology’s ripple effect on system performance. Within the industry, there is a race to the top in terms of performance and quality, and bifacial modules, which are 1,500-volt compatible, make up the next frontier. Here we discuss the competitive advantages of bifacial modules for installers and the design strategies to take full advantage of the technology for ground-mount and tracking systems.
The manufacturing costs of bifacial modules—a key driver behind price—are similar to those of conventional passivated emitter and rear cell (PERC) modules. The biggest cost difference between a PERC module and a bifacial module comes from adding glass to the backside instead of a back sheet.
The benefits of bifacial modules are multifold. The use of high-yield modules brings an economic advantage to a solar power plant: Using a higher power density product, installers can achieve the same system size and output with fewer modules compared to a conventional system. Since less modules and system inputs are needed, bifacial modules provide savings on reduced BOS costs such as cabling, racking, labor and land. Additionally, a higher yield and higher quality product delivers improved system LCOE.
In some cases, utility-scale projects have more to gain from advanced solar technologies, such as trackers, given the systems’ greater economies of scale and subsequent returns. The market is responding to these benefits: LONGi Solar had 100 MW of bifacial orders in 2017. In 2018, LONGi expects that number to increase.
In 2017, LONGi supplied 20 MW of bifacial modules for a 100 MW ground-mount installation in the Qinghai province of China—the world’s largest bifacial solar installation. This project was equipped with single-axis trackers with a post height at 2.2 meters and an approximate 45% ratio of module area to land area, or ground coverage ratio (GCR). Let’s unpack what those design parameters mean.
As more developers look to include bifacial modules into their system design and are modeling their bifacial utility-scale systems within the local conditions and size parameters, they must consider several factors for optimized siting and installation.
Selection of the background is a first consideration when understanding the system’s performance, as bifacial modules will capture more energy from more reflective surfaces. Reflective materials such as metals can reflect approximately 85% of solar radiation, while snow reflects approximately 70%.
For ground-mount systems, mounting considerations include GCR and racking height, since the higher the racking, the more irradiation the bifacial modules can capture. A lower GCR brings more light to the backside of the module and improves backside energy yield.
Tracking systems for PV power plants are another important factor for system optimization. In conventional ground-mount systems, bifacial modules can offer 10%–15% higher energy yield before integration with advanced technologies such as trackers. Combining bifacial modules with single-axis trackers can increase total energy yield by 20%–30%. In a study that used LONGi’s bifacial modules in the Kubuqi desert in China, the energy yield gain from the bifacial and tracker system was about 26.7% with the specific bifacial gain around 15.9%. LONGi is working with tracker companies to assess the pros and cons of each design and their impact on bifacial energy yield.
As more and more projects integrate bifacial modules and the returns on the technology is further proven for the market, we see bifacial modules as being a breakthrough technology in the utility space and the larger solar energy industry.
—LONGi Solar Technology / Shaanxi, China / longi-solar.com