Could thin-film solar panels be making a comeback? If you believe the whispers in the hallways at conferences, the answer may well be yes.
First, a quick overview of the thin-film market as it stands now. While there are a number of thin-film solar providers, two are well-known companies distributing thin-film panels in the United States: First Solar and Stion. A third, Siva Power, is still building its factory, but it expects to come online soon.
There are two competing technologies: cadmium telluride (CdTe) and copper indium gallium selenide (CIGS). First Solar, the largest producer of thin-film panels in the United States, uses the former. Stion and Siva Power (when they start producing panels), use the latter.
Less than five years ago, thin-film panels, because they were cheaper to produce, were going to revolutionize the industry. But when silicon prices dropped quickly, they lost that momentum. With silicon prices finally leveling out, however, it may present thin-film with a chance to re-emerge —at least according to Frank Yang, VP of Business Development for Stion.
“There is opportunity for the right thin-film technology, one that competes with silicon PV on levelized cost of electricity (LCOE),” Yang says. “CIGS modules have a proven energy-yield advantage in warm climates due to superior temperature coefficient.”
According to Brad Mattson, CEO of Siva Power, CIGS modules have a number of attributes that lead to superior field performance and financial returns for project owners.
“CIGS is a demonstrably capable and versatile material,” Mattson says. “The world records for thin-film efficiency are all held by CIGS. This is significant. It opens up the possibility of the Holy Grail in solar: Silicon-like efficiencies at low thin-film costs.”
Yang says that adding sulphur (making traditional “CIGS” into “CIGSS”) adds a second layer of protection from degradation over the long-term.
“Dual-glass CIGSS modules with an effective edge seal have been proven to be the most stable commercialized PV semiconductor as demonstrated by test arrays at national labs with over eight years of field testing that exhibit zero degradation,” Yang says. “CIGSS modules have a superior temperature coefficient leading to better yield than crystalline silicon modules in warm climates.”
But there are a couple of problems holding thin-film solar back:
1) Thin-film technologies have traditionally had lower efficiencies than silicon panels (although some new lab testing showed at least one panel that produced a 23.2% efficiency, which indicates that may be changing).
2) The different production methods have hindered production on a wider scale.
But the companies currently involved see those challenges as more opportunities than obstacles. Yang says his company’s current technology, single-junction CIGSS modules, has a conversion efficiency of approximately 14% and a superior temperature coefficient (-0.26%/°C). The temperature adjusted efficiency is on par with crystalline silicon modules enabling equal or better project value in most climates.
And Mattson says he believes the best production method has been recognized and will revolutionize thin-film production —as soon as this year.
“It turns out that the optimal choice is now clear: three-stage co-evaporation with monolithic integration on glass not only results in the best process at the lowest cost, it has the promise of reaching silicon efficiencies at thin-film costs,” Mattson says. “In fact, it might be the only technology that can get us to the fabled land of a sustainable $0.40/watt.”
From Yang’s perspective, the future for thin-film —as well as the rest of the industry —looks bright.
“The industry is entering a new phase of growth that will include investment in manufacturing expansion for the right technologies,” Yang says. “Investors will look for those that deliver differentiated project solutions —and we’re betting on thin-film solar being one of them.”