Solar photovoltaic (PV) power led the increase in renewable energy generation around the world in 2017, with capacity growing by as much as a third during the year. What if there was a way to increase the power generation of solar photovoltaic panels by up to 15% and even as much as 50% under ideal conditions? In theory, bifacial technology can deliver this. So is bifacial technology about to become a mainstream technology?
Unlike traditional monofacial panels, bifacial panels are capable of capturing solar irradiation from the front and back. This means they have the capacity to generate power from the sun by capturing the sunlight reflected from the ground, as well as direct sunlight, therefore increasing the total energy generation. As standard crystalline solar cells used during the past 30 years are reaching their physical limits, the PERC (passivated emitter and rear cell) structure is enabling manufacturers to achieve higher efficiencies. As the technical know-how to introduce PERC technology has become available along the value chain, it constitutes a new viable platform to manufacture high-power and high-efficiency solar panels. The number of manufacturers producing bifacial panels is increasing, and there is a corresponding increase in the number of installations. There is no standard design as yet, with varying design criteria from framed and frameless, monocrystalline and polycrystalline designs.
There are a number of important considerations as to the viability of deploying bifacial panel arrays. Most important is the ground albedo – or whiteness – which affects the amount of underside light that is reflected. This could be light-colored stone, reflective paint, foil or even grass. In trials, a foil surface, which has an albedo of 80%, contributed an additional 20% power, compared to grass, which has an albedo of 30% and contributed only a 9% power gain. Added to this, each surface will need a different maintenance profile and be affected by a range of factors, including the prevalent weather conditions.
In addition, the panel arrays’ pitch, height and tilt, as well as the mounting system design, cable management and inverter selection, all impact the amount of shading, hence the available active surface of the back of the panel. This means bifacial technology is best suited for flat rooftops and ground-mounted arrays to allow for room to optimize the tilt to bounce the reflected light on to the rear of the panels.
So far, the uptake of bifacial technology has been inhibited by the difficulty in predicting performance with a level of certainty. In 2015, bifacial modules had only a 5% market share. Test facilities are in operation around the world to observe the yield gain of bifacial modules – from New Mexico (the Sandia Lab experiment was conducted in Albuquerque in 2012) to Japan (a 1.25 MW demonstration plant in Asahikawa, Japan, saw a 21% annual yield gain after 32 months in operation in 2013).
Another inhibitor has been the cost of the panel production, due to the complex cell structure and amount of silver paste required. But even considering potential increases in installation and panel costs, bifacial technology plays an important role in further reducing the levelized cost of electricity (LCOE) through increased power yield and extended lifetime.
Bifacial modules are becoming a commercial reality: Most module manufacturers are switching to PERC module production lines and starting bifacial production, and the total installed bifacial capacity is estimated to reach 5 GW by 2020 and 40% market share by 2025. There are still challenges that need to be overcome, including the lack of global standard testing procedures for rating bifacial modules, capex increases, difficulties in modeling the power gain with accuracy, the need for field testing, the risk of potential induced degradation and the lack of uniform back irradiance, among other factors. Yet the prize appears worth it. Power can be generated from a smaller footprint; plus, as manufacturing costs continue to decrease and the module quality improves, the increased generation and lower LCOE point to bifacial technology entering the mainstream.
Overall, the potential impact of bifacial technology is fivefold. With the technology innovation taking hold, we should expect to see a significant growth in market share over the next five years. Continued trials will crystallize performance predictability and show us how to maximize the yield increase, which in turn will drive uptake. Bifacial technology may have a slight additional installation cost over monofacial PV systems, but even a conservative bifacial gain should outweigh the risk. Bifacial technology is an important enabler in reducing LCOE through increased power yield. And finally, this potential for a smaller footprint could unlock new, unexpected uses for solar. It will be interesting to watch.