Solar Materials of the Future are Great on Performance. But What About Toxicity?May 11, 2020 by Tyler Charboneau
The materials in solar photovoltaic panels can be toxic when improperly disposed of. Are alternative materials any better?
Solar photovoltaic technology’s promise as a sustainable platform has been scrutinized since its invention in 1954.
The Bell Solar Battery was announced in 1954. Image used courtesy of John Perlin/AT&T Archives
Multiple improvements—and integrations with electronics—in recent decades have vaulted solar energy into mainstream use. However, developers have yet to overcome some major environmental concerns, in spite of their overall progress.
Is Solar Tech Actually Eco-Friendly?
Solar photovoltaic technology’s eco-friendliness has traditionally been its calling card. According to Professor Michael D. Mehta in an article on next-generation solar panels, the current panel market is dominated by crystalline silicon, a material boasting 15–20% efficiency in commercial applications.
Stacked crystalline silicon solar modules. Image used courtesy of Michael Mehta
But this green energy isn’t free—and may even be a misnomer depending on your perspective.
The photovoltaic lifecycle has environmental drawbacks concerning production and disposal; the material within the panels that are chiefly responsible. According to a Forbes article on solar panel toxic waste, these include:
The Forbes contributor, Michael Shellenberger, explains that roughly 90% of solar panels are constructed from glass. The rise of solar panels worldwide will require a large production effort, necessitating greater glass consumption. Let’s not forget silicon demands as well. The former isn’t problematic in itself, but potential issues magnify at scale.
Infographic of the distribution of solar panel waste. Forecasts for PV waste by 2050 have since increased to 78 million tons. Darker colors indicate higher concentration of PV waste. Image used courtesy of Green Match
Glass is paired with those aforementioned materials during panel production, which causes problems down the road.
The Problem With Lead
Lead contacts the glass foundation in many panels, often in the form of wiring. Unfortunately, lead has a habit of leaching into other materials. Environmental concerns associated with this are growing annually. For example, the International Renewable Energy Agency (IREA) expects global solar panel waste to measure 78 million metric tons by 2050. While the lead present in one panel isn’t necessarily a cause for concern, deposition at this scale is alarming.
Projection of global PV panel waste between 2016 and 2050. Image used courtesy of IREA
The danger that lead poses to humans through contact, contaminated water, and tainted soil is well documented. Wildlife is also susceptible to lead poisoning in various forms. Solar panels at the end of their life forego landfills due to soil contamination concerns. They also can’t be recycled easily; glass impurities due to lead contamination prevent it. We can say the same for both plastic and cadmium in solar panels.
It's important to note, though, that solar photovoltaic systems leave less than half the environmental footprint that nuclear energy does and are nearly four times greener than coal, according to Mehta. The disposal conundrum is driving developers to seek promising new solutions.
Introducing Next-Gen Solar Solutions
Researchers have adopted a two-pronged approach to solar innovation. This effort centers on using new materials while applying them in novel ways—ways that will directly affect electrical engineers. Solutions gaining popularity are as follows:
- Cadmium-telluride thin-film modules
- Other thin-film photovoltaics, including carbon fullerenes
- Quantum dots
We’ll break down the technology behind each while offering an environmental assessment. These alternatives carry unique promise, but we’ve yet to collectively stumble on a perfect solution.
Cadmium-Telluride (CdTe) Modules
Flexible semiconductors do wonders for the electronics world where flexibility and real-estate optimization are crucial. Solar energy purveyors are adopting a similar approach with cadmium-telluride thin-film modules. Engineers can apply these films to curved and flat surfaces alike—even if such surfaces are made of glass, stainless steel, or plastic. They’re also lightweight. Older photovoltaics have set a developmental precedent, yet don’t share these properties.
On the efficiency side, a typical CdTe module claims a conversion efficiency of roughly 6%. While traditional crystalline silicon eclipses this handily, laboratory CdTe modules have reached efficiencies up to 22.1%. They’re inexpensive overall and are the second-leading solar implementation today. They use 99% less silicon than other panels.
Solar PV technology. Image courtesy of the U.S. Department of Energy
These benefits aren’t without drawbacks. Thin films are naturally more vulnerable to wear over time. External exposure to climate conditions causes degradation in a shorter span. These coatings require more maintenance.
Cadmium is also highly toxic—approximately ten times more than lead. Each thin-film panel has a certain cadmium concentration. A National Institute of Health study found that 73% of a panel’s cadmium concentration can leach within a municipal landfill in just 30 days. That solubility of cadmium in an effluent—an outflowing of liquid waste to rivers or seas—is high.
Landfill disposal leads to cadmium leakage, which can poison aquatic life and the water table. The CDC reports that in humans, cadmium exposure can cause respiratory disease, kidney disease, and cardiovascular issues. Should we adopt lower-efficiency modules, even higher quantities of these chemicals will be disposed of—since engineers may offset inefficiencies with increased surface areas.
Thin-Film Carbon Fullerenes
Solar photovoltaic developers are also harnessing organic compounds in energy conversion. A thin plastic film serves as the base for a concoction of ink and molecular carbon. These nanocarbons are dubbed carbon fullerenes. These spherical fullerenes have conductive muscle. 2018 research from the University of Michigan demonstrated that nanocarbons can help electrons travel several centimeters. This promotes electrical flow across the panel on a grander scale.
The breakdown of silicon-based PV panels vs. thin-film-based PV panels. Image used courtesy of Green Match
The bonds between organic molecules are loose, making it easy for electrons to stagnate. Researchers have solved this problem by tweaking fullerene properties. The logical next step involves an arrangement in a grid. Film manufacturers have dissolved these fullerenes into ink and bonded them across that plastic layer.
These are incredibly light and flexible. However, the chemical and physical stability leaves something to be desired. Accordingly, the lifespan of thin-film carbon fullerene isn’t long. Efficiency issues necessitate the application of the compound across wider surface areas as well.
While we’re accustomed to quantum dots within our displays, their solar energy potential is increasingly being explored. Mehta explains that this manufactured, crystalline layer transports electrons more readily than its thin-film counterpart. It’s often used for buildings, cars, and other large surfaces with plenty of exposure to sunlight.
The knock on quantum dots is durability; the material is thin, fragile, and hard to apply evenly. This can impact structural integrity—especially in the face of outdoor wear and tear. Thankfully, users can achieve up to 10% efficiency with quantum technology.
Balancing Photovoltaic Progress and Toxicity
No technology is perfect. Each brings its own benefits and drawbacks to the table.
While these next-gen photovoltaics show promise in higher efficiency, it's important to balance this strength with the risk of increased toxicity. Finding a balance (and hopefully new innovations with the best of both worlds—efficiency and eco-friendliness—will help researchers, engineers, and consumers find a sustainable solution for decades to come.