Feb. 28, 2022 

By Aaron Thurlow
General Manager, Distributed Generation

The commercial and industrial (C&I) sector has been called the underdog in the U.S. solar market, usually playing second fiddle to its larger and more visible residential and utility segment siblings. But C&I’s ultimate multi-gigawatt potential has never been in dispute. A 2020 report by Wood Mackenzie estimated there was enough unused commercial roof space to accommodate 145 GW of solar PV installations. Some 600,000 sites, or about 70% of the total commercial real estate building stock in the U.S., could be solarized.

The latest U.S. Solar Market Insight report shows commercial solar experiencing a growth spurt. Several factors are at play in the growth trend, including an extended federal Investment Tax Credit, multiple state-level incentive programs, and an increased interest in environment, social and governance (ESG) investments. Years of industry efforts to reduce friction points and more compelling system economics in the C&I sales and development process are also finally helping the sector achieve its long-term promise. Better financing options, the emergence of energy storage, advanced software modeling and sales tools, construction efficiency, and the streamlining of permitting and interconnection are all contributing factors as well.

This blog will not delve into the layered idiosyncrasies of the C&I market, but instead focus on a particular solar technology that could help accelerate the sector’s growth. An innovation that is already changing the utility solar space shows the potential to help take the commercial sector to the next level of system performance as well—bifacial solar modules.

Bifacial PV—An Already Compelling Rooftop Option

Bifacial modules are not new but have only recently emerged at scale and at a price point that is competitive with monofacial modules. They offer several key advantages that the utility space honed in on quickly. The same value propositions that make bifacial such a compelling option in the utility space could apply to the C&I market and its core rooftop segment, which is often overlooked for bifacial.

More energy density, lower labor and balance-of-system (BOS) costs, increased lifetime plant performance, and the like combine to make bifacial an attractive, bankable option offering better returns for larger rooftops. Because bifacial modules generally produce more kWh/kWp,  there is built-in design flexibility and optimization possibilities—one can upsize system output versus a monofacial-based design or keep the rated output the same with fewer modules and BOS components.

There is a misconception that the backside performance of a bifacial module must be optimized to have a better project return; however, this is not the case now that bifacial module pricing has come down to within a penny or two per watt of monofacial. Bifacial provides real value to  rooftop installations today even without backside power optimization.

Since many bifacial modules use a glass-glass design, they are sturdier and more fire resistant. Bifacial modules also degrade more slowly than standard monofacial modules, resulting in performance warranties being extended to 30 years. A slower degradation curve coupled with five more years of warrantied power makes a major impact on the system LCOE and lifetime output of the system. It may also allow for better financing options.

Benefits of Bifacial Energy Gain

Of course, the largest potential benefit is the inherent bifacial energy gain—somewhere between 5% and 25%, depending on albedo, site design and other factors—coming from the backside of the module. Keep in mind that the bifacial gain is not included in many modules’ spec sheet power rating (including LONGi’s): the gain is additive to nameplate. So a 445 W bifacial module is effectively more like a 490 W module.

Using an example where less capacity needs to be built, a 500 kW bifacial PV rooftop system with 8% average gain, built at a cost of $2/watt, would actually end up with a savings of $80,000 compared to a monofacial system of the same size: a 500 kW install would require 1,124 445 W monofacial modules, but a bifacial array would only require 1,034 bifacial modules. Plus, this back-of-the-envelope calculation does not factor in a longer system lifetime or a slower degradation curve.

This blog is adapted from an article in the September 2021 global edition of pv magazine:  https://www.pv-magazine.com/magazine-archive/both-sides-for-ci/ .