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Going big on bifacial solar

Renewable energy developer Invenergy is deploying large-scale bifacial solar module technology on the massive Southern Oak solar power project that is now under construction in Georgia.

By Tony Kryzanowski

As with a new vehicle, what really drives performance on a solar power installation is what's under the hood.

A good case in point is Invenergy's large-scale, 160-megawatt (MWac) Southern Oak solar power project currently under construction in Georgia, which features bifacial solar module technology.

Invenergy is a leading privately held developer and operator of sustainable energy solutions, with over 15 gigawatts (GW) of operating wind and solar assets. Because of its leadership, industry takes notice of the equipment choices Invenergy makes. Southern Oak is the company's largest solar project to date, at least 100 MW (ac) larger than any of its earlier projects.

Its customer for Southern Oak is Georgia Power, which issued a request for proposals (RFP) in 2017 for utility-scale solar projects as part of its Commercial & Industrial Renewable Energy Development Initiative (C&I REDI).

Invenergy had already established itself in Georgia as a solar power developer, with its Lakeland solar farms. Power from that installation is also sold to Georgia Power. Invenergy had been planning another solar project in Mitchell County, Georgia, for about eight years.

The Georgia Power RFP provided the opportunity to significantly expand the scale of that project, and Invenergy was successful in securing a 30-year power purchase agreement (PPA) for solar power generated by Southern Oak. Its 160 MW will provide enough renewable power for 30,000 households.

Construction began in November 2018 and is on schedule for completion by the end of 2019. Renewable Energy Systems (RES) is the construction contractor on the project.

In addition to purchasing all of the energy generated by Southern Oak, Georgia Power also has the ability to claim all renewable energy credits (REC) till 2049.

Bifacial solar modules have the ability to generate power from both sides of the solar panel, with the typical opaque cover on the module backside replaced with glass. The back of the module is able to produce power from light reflected off the ground and from diffused light.

The amount of additional power the bifacial module will generate is variable from location to location.

"In general, bifacial modules will produce more than a monofacial module on a nameplate basis," says Paul Thienpont, manager, Renewable Engineering at Invenergy. "It really depends on the environment and the climate that they are in."


For example, he says obviously more light will be reflected off snow-covered ground than off a dark, earthy cover.

The Southern Oak project features LONGi-brand, PERC Hi-MO2 bifacial modules combined with NEXTracker single-axis trackers, as well as what NEXTracker describes as its state-of-the-art TrueCapture control system.

Mike Kaplan, vice president, Renewable Development at Invenergy, says that there were greater upfront costs to implement this technology on the Southern Oak project, but the payback in greater yield made the investment worthwhile.

A bifacial module on a tracking system is going to be more expensive than something on a fixed-axis mount, he says. "But the additional CAPEX is more than offset by the additional energy yield over time."

However, the quantity of additional power they anticipate will be generated from using bifacial modules at Southern Oak is being kept under wraps for competitive reasons.

In a press release related to the use of its bifacial module technology at Southern Oak, LONGi steers clear of any reference to what is expected from this specific project, but says that in a desert environment where there is high reflectivity, the combination of its bifacial solar module with a flat uniaxial tracker can increase power yield by 25 percent compared to the traditional monofacial module plus fixed-rack PV system. The yield gain from the module underside alone is pegged at 10 percent.

Kate Woodson, Invenergy project manager, Renewable Project Management, is leading the construction effort at Southern Oak and says there is nothing significantly out of the ordinary when installing these bifacial modules compared to a standard project with monofacial modules.

"We tend to handle these double-sided modules with a bit more care because of the backside component," she says, "but from a construction standpoint, there is nothing atypical compared to a monofacial module." TMEIC supplied the inverters for the Southern Oak project.

While not as robust as the southwest desert environment, Georgia is described as having an upper tier solar resource compared to other areas of the United States.


Bifacial solar modules have the ability to generate power from both sides of the solar panel, with the typical opaque cover on the module backside replaced with glass. The back of the module is able to produce power from light reflected off the ground and from diffused light.


"The southeast in general is really an emerging market for solar," Thienpont says. "As a whole, Georgia is an area that is certainly going to see quite a bit more solar installations happen, along with the rest of the southeast."

Deployment of the bifacial module technology and a tracking system was not critical to the project's economic viability, "but we always look to use the most innovative and most cost-competitive technology," says Kaplan.

Asked whether Southern Oak is a test case for this combination of bifacial module and tracking technology for potential deployment in future projects, Kaplan responded that Invenergy always deploys commercially-proven technologies, but is constantly innovating to deliver wins for customers, landowners, and communities.

"This technology has proven itself already," he says. "It just hasn't been deployed at the scale that we are now deploying it. Having more options to choose from can complicate procurement decisions moving forward," he added.

In addition to providing about 400 construction jobs, the Southern Oak project is expected to generate more than $12 million in local economic development by way of tax payments, lease payments to participating landowners, and wages and benefits to employees in the first decade of the 30-year PPA alone.

Paige Gilchrist, executive director of the Mitchell County Development Authority, says that the Southern Oak solar project is the largest, single investment ever made in Mitchell County. Although the county has other solar installations, Southern Oak is more than two times larger than the next largest project (70 MW) currently under construction.

The county and local residents were very pleased with the investment, as over the short term, with about 400 construction workers on site, "this provided a good boost to our sales tax by construction workers eating at our local restaurants, buying gas, shopping at local retail stores, and lodging," says Gilchrist.


In Georgia, one of the main weather concerns is the threat of hurricanes. Local building codes take this force of nature into account when permitting solar power projects, and Southern Oak was no exception.


Over the longer term, the extra tax income derived from the project will help to temper the need for future tax increases, "without putting any cost or burden on the county. It did not have to use tax dollars to make this project work."

The Mitchell County Southern Oak location, which is about 35 miles south of Albany, in southwestern Georgia, was close to a transmission line interconnection, in an area that is not densely populated and is relatively flat and dry.

In Georgia, one of the main concerns is the threat of hurricanes. A hurricane did occur in the Mitchell County area just prior to the start of Southern Oak construction. Local building codes take this force of nature into account when permitting solar power projects, and Southern Oak was no exception.

Thienpont says that Invenergy always keeps its ear to the ground about evolving technologies.

"Bifacial in general is something that has been in labs for quite some time, and it has been deployed in other areas of the world, but not necessarily at this scale in the U.S.," he says. "In terms of the Southern Oak site, it was something where the timing of commercial, large-scale production lined up nicely with this project, which led us to be able to use it here."

There are options in the marketplace, he added.

"If you travel to any of the trade shows, you'll see that nearly everyone has a bifacial panel at their booth," Thienport says. "The question is how much volume do they have and how serious are they about it.

I think that as a whole, the industry is starting to adopt new and evolving technology at a more rapid pace than the industry has in the past."

It would not surprise him to see more projects featuring bifacial module technology put into production in the foreseeable future, based on where the technology roadmap is going and the tight margins emerging from PPA negotiations generally.

"As far as where the crystalline silicon market is going, bifacial is a natural progression of the technology and as the lending community and others become more comfortable with it, I think you will see it become more prevalent," he says.

As with module technology, tracking system technology has also evolved over the past few years, including the anticipation of greater use of bifacial modules, with systems like the NEXTracker system designed to work well with it.

For his part, NEXTracker founder and CEO Daniel Shugar recently wrote on the company website that he has been talking about bifacial module technology for a couple of decades. The company has been actively conducting testing of bifacial modules for four years at its Center for Solar Excellence with several third-party evaluators, including the National Renewable Energy Lab (NREL). Shugar says the company has about 750 MW of bifacial projects in its pipeline.