100 Gigawatts Of CdTe Thin Film Solar Possible By 2030

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Despite the sudden U-turn in US energy policy, solar innovators in the US continue to push the renewable energy transition forward, here at home as well as globally. The latest example comes from Ohio, where a research team has outlined a pathway for the US to produce 100 gigawatts (DC) of CdTe thin film solar per year by 2030.

The CdTe Thin Film Solar Difference

For those of you new to the topic, CdTe is short for cadmium telluride. In contrast to the more familiar silicon solar cells technology, CdTe falls into the thin film solar slot. It is mixed in a solution and spread or grown on sheets of glass.

The thin film solar manufacturing process is completely different from silicon fabrication. It offers the advantages of lower cost, higher volume, and a lower energy footprint. Advocates for CdTe thin film in the US point out the advantages of a domestic supply chain. They also cite the benefits of diversifying the nation’s solar manufacturing industry.

That helps explain why CdTe plays a significant role in the US solar industry, though it is not commonly used elsewhere around the globe. As of 2023, about 17% of installed solar capacity in the US consisted of CdTe thin film, primarily in utility-scale applications. Globally, CdTe only accounted for about 3%.

100 Gigawatts Of Thin Film Solar, Per Year

As for why global uptake is so low, part of the reason is the relatively low conversion efficiency of thin film solar compared to silicon. Nevertheless, with the benefits of thin film solar in mind for the purposes of domestic energy security and job creation, the US Department of Energy has spent decades collaborating with industry stakeholders to improve CdTe technology.

Among those stakeholders is the Ohio-based firm First Solar, which spun out of research at the University of Toledo. First Solar has been collaborating with the Department of Energy for more than 30 years (see lots more First Solar background here).

The latest product of the partnership is a new, detailed roadmap for achieving 100 gigawatts in domestic CdTe thin film manufacturing capacity per year, in the form of a study published in the peer-reviewed journal Joule under the title, “Roadmap to 100 GWDC: Scientific and supply chain challenges for CdTe photovoltaics.”

CdTe thin film solar already has a running head start on scaleup. “Cadmium telluride solar cells are the only other photovoltaics to be manufactured at the gigawatt scale, enjoying a particular niche in utility-scale deployment,” the Roadmap research team explains, with silicon being the other one.

Clearing The Obstacles Along The Way

There being no such thing as a free lunch, before CdTe manufacturing in the US can scale up, the industry needs to address two obstacles.

One limitation is the domestic supply of tellurium, which is the key ingredient in telluride compounds. Last year, the US Geological Survey added tellurium to its list of critical materials, indicating an increased focus of attention on the supply chain by federal policy makers.

“Tellurium is primarily recovered as a byproduct of the electrolytic refining of copper, where it accumulates in the residues of copper anodes,” USGS explains.

“In 2023, two electrolytic copper refineries operated in the United States, one in Texas and one in Utah (this one), and produced copper telluride from tellurium-bearing anode slimes,” USGS elaborates, noting that CdTe thin film solar manufacturers are not the only market for tellurium. It is also a key ingredient in the compound BiTe (bismuth telluride (BiTe), used in the thermoelectricity field.

The new Roadmap goes into the tellurium supply question in detail, concluding that the amount available to the thin film solar industry can be increased by improving existing extraction technologies.

Making Thin Film Better

The other angle of attack is to improve the solar conversion efficiency of CdTe thin film. The Roadmap team notes that breakthroughs were hard to come by for a period of time, but 2023 proved to be a breakthrough year.

Specifically, the team attributes the improvement to the introduction of group V elements as a dopant in the fabrication of CdTe film, as an alternative to conventional methods deploying copper and other metals. Group V on the Periodic Table of Elements includes vanadium, niobium, tantalum, and dubnium.

“Four new cell efficiency records were certified at NLR over a 15-month period,” the research team noted last year, referring to the Energy Department’s National Laboratory of the Rockies (formerly NREL, the National Renewable Energy Laboratory).

A study published in 2021 explains the group V difference:

“CdTe solar cell technology is one of the lowest-cost methods of generating electricity in the solar industry, benefiting from fast CdTe absorber deposition, CdCl2 treatment and Cu doping. However, Cu doping has low photovoltage and issues with instability. Doping group V elements into CdTe is therefore a promising route to address these challenges.”

Of the four new CdTe formulas recently certified by NLR, the record-setter is First Solar at a respectable 23.1%. The research team also notes that, while First Solar and other manufacturers are currently using copper as a dopent, the transition to group V doping is already underway.

Next Steps For Thin Film Solar

The new Roadmap is the work of many hands, including First Solar and the Wright Center for Photovoltaics Innovation and Commercialization at the University of Toledo, along with along with NLR, the Missouri University of Science and Technology, Colorado State University, and Sivananthan Labs.

For the record, the team was organized under the Cadmium Telluride Accelerator Consortium, which is administered by NLR with the University of Toledo in the lead. So … how is the Cadmium Telluride Accelerator Consortium still up and running, considering the fossil-friendly direction of US energy policy. Good question! If you have an answer, drop a note in the comment thread.

Before you do, consider that CTAC is a three-year program funded by the Solar Energy Technologies Office at the Energy Department in 2022, as part of a broader initiative to get new solar energy technologies into the marketplace, more quickly, and at a lower cost.

Whether or not CTAC lives on, First Solar has not been letting the grass grow under its feet. On November 21, First Solar announced the start of operations at the newest facility in its US portfolio, a new, $1.1 billion, 3.5-gigawatt beast of a solar factory in Louisiana’s Iberia Parish.

On November 1, word also slipped that the company was already planning another solar factory in the US. Sure enough, just two weeks later First Solar officially tapped the South Carolina city of Gaffney for the honor.

“The facility is expected to increase First Solar’s capacity to produce American-made solar technology that is fully compliant with anticipated Foreign Entities of Concern (FEOC) guidance, by 3.7 gigawatts (GW), reaching 17.7 GW of annual nameplate capacity in 2027,” First Solar explained.

As for who’s going to buy all that new thin film solar technology, that’s another good question….

Photo: The CdTe thin film solar manufacturing industry has an opportunity to grow to 100 gigawatts per year in the US as soon as 2030, according to an industry-academic research team (courtesy of First Solar via US DOE).