Bifacial solar PV technology has long been a novelty.

But pilots announced this summer — including a new Soltec bifacial tracker test center in California, plus a partnership between Array Technologies and a national lab in New Mexico — suggest bifacial is edging toward the mainstream. But manufacturers still need to dial back costs.

Before bifacial modules are ready for widespread adoption, manufacturers say the industry has a year or two of data collection to determine how they compete in both efficiency and cost, and what applications they're most effective for.

“Once everyone understands the costs and the implications and can understand the problems, well, the problems get simplified,” said Array founder Ron Corio. “We’re in that simplification process right now.”

The company recently installed two rows of bifacial modules — from manufacturers Longi, JA Solar, Trina, Jolywood, Hanwha Q Cells and Canadian Solar — at a New Mexico national laboratory to test the modules with its trackers and create simulation models from the test rows.

Because bifacial modules collect sun from both the top and the bottom of the panel, they present unique challenges in siting and installation.

“That’s the thing about bifacial,” said Corio. “It’s a big bucket of variables.”

At its new installation site, Array is testing variables like how mounting offsets impact irradiance. In bifacial installations, developers must consider factors including ground albedo, ground cover, irradiance and system design, like trackers, to maximize output.

Those variables add up to one of the technology’s greatest challenges: quantifying power output.

“People understand the variables that make a difference, but they don’t understand how to calculate the actual difference based on those variables,” said Tyler Stewart, vice president of sales and business development at bifacial module company Prism. “If you don’t understand what the backside performance is on the module, then the height, the tilt, or whether it’s on green grass or white snow is kind of a moot point. If your back only produces half as much power as the next [product], and you don’t know that difference, it’s hard to calculate how it’ll actually perform.”

“I think truly the biggest hurdle to that is there’s not a standard,” he added.

Stewart thinks that the next couple of years will change that. The International Electrotechnical Commission, along with testing agencies such as the National Renewable Energy Laboratory and Sandia National Laboratories, has been working on a uniform standard and released a proposed measurement standard. Stewart expects it to be finalized soon.

For now Prism tests the front and back of its modules separately against a black backsheet. Testing against a white sheet can inflate the standard test conditions rating, according to Stewart.

Though the standard hasn’t yet been finalized, Dr. Hongbin Fang, director of technical marketing at Longi Solar, said a module’s backside production can increase energy yield by 15 percent* and possibly more, depending on location and how a bifacial module is installed.

That’s drawn attention from large manufacturers, as well as smaller companies like Prism.

Longi contributed 20 megawatts to a 71-megawatt bifacial project in China — which the firm describes as the world’s largest bifacial solar project — connected in January. And Fang said demand is growing.

“Right now, I think bifacial is a very small portion of...the product mix in the overall industry,” said Fang. “Probably in the next one or two years, once you have this bankability established, the backside gain on the bifacial system established in the market, we believe most of the customers will switch to bifacial.”

While Prism has a several-year pipeline of several hundred megawatts, Longi said it shipped about 100 megawatts of bifacial last year and it currently has hundreds of megawatts' worth of orders.

“We’re at this point where there’s a lot of leading suppliers that have scaled bifacial capacity and there’s a whole bunch of suppliers doing pilot projects in China, the U.S. and Europe,” said Jade Jones, a senior solar analyst at Wood Mackenzie Power & Renewables. “The barrier that’s happening right now is figuring out how to standardize power estimates for these products across the board.”

Once the standard is in place, it will be easier for the industry to assess the benefits of bifacial modules against their cost. Monofacial and bifacial modules are moving closer to cost parity. Bifacial requires few manufacturing tweaks, such as replacing the traditional backsheet with glass, compared to monofacial production.

“I think it’s similar to single-axis tracker adoption. You have a little bit of a higher cost, but you deliver a higher energy yield. This is a levelized cost of energy solution,” said Fang. “This will take a little bit of time, probably one to two years for the technology to become established with customers, as well as by tracking real performance data. Once that is realized, we think the switch to bifacial will take off very quickly.”

Kimberly Weaver, Array’s lead engineer of bifacial products, said manufacturing costs have come down enough to make bifacial prices comparable to monofacial. “That’s where this high visibility on bifacial is coming into play,” she said.

But a dearth of actual field installations means more data is needed. Until that rolls in, barriers to adoption remain.

“People still don’t quite understand how to utilize them, therefore the manufacturers don’t see the cost-benefit of making them in volume yet,” said Stewart. “In my eyes it’s a no-brainer, but I’m a little biased.”

Jones, too, said deploying bifacial becomes a “no-brainer” when the economics are right.

“As long as pricing is within the buyer's range, and it makes sense in terms of the economics, bifacial is such an easy win,” she said.

Array will start collecting data on its newly installed panels next week. The tracker company said it should have enough data by November to come to some conclusions about the technology.

“I think the utility markets are just starting to get a better understanding of its capability,” said Stewart. “It’s only a matter of time before it catches on in that space.”

*This number has been changed to reflect efficiency numbers from Longi.