The Dark Side of Solar
A Clean Technology Has a Dirty Side—but It’s Improving
To a world desperate to break its fossil fuel habit, solar energy looks almost like magic: a free, infinite wellspring of electricity pulled directly from the heavens with no carbon footprint at all. It is the wunderkind of the clean energy revolution, multiplying across rooftops and desert basins at breakneck speed. But beneath this gleaming, ecofriendly surface lies an uncomfortable paradox.
Every solar panel deployed to save the planet carries a dirty secret—a heavy environmental debt incurred before it ever generates a single watt. From the emissions spewed by coal-powered silicon smelters to the toxic metals and resins in discarded panels, the assets powering the clean future remain tied to the very pollutants society is trying to eradicate.
If solar is truly going to deliver on its promise as the ultimate green savior, it must first confront its own dark side.
70 Years of Solar
First developed in the 1950s, solar photovoltaic (PV) cells have in recent decades expanded to utility-scale power generation. This application is growing rapidly.
According to the US Energy Information Agency, utility-scale solar is the fastest-growing source of electricity generation in the United States, and that trend is projected to continue. Yet, the technology still has a long way to go. It currently accounts for less than 10% of total US electricity generation.
However, at current growth rates, and coupled with other rapidly expanding forms of clean power, such as wind and geothermal, these renewable sources could conceivably displace fossil fuels at some point in the future and perhaps even make them obsolete. In this scenario, the energy industry would have finally cured itself of its fossil fuel dependence.
[Silicon is extracted] in smelting furnaces fueled by sustained and intensive heat currently generated mostly by fossil fuel–produced electricity.
Unpacking this issue reveals that the problem spans both ends of the technology’s life cycle. Solar cells are composed of highly refined silicon, a gray, shiny “metalloid” that has properties of both a metal and a semiconductor. It is extracted from quartz rock or sand through a process that consumes carbon-emitting materials such as coal. Furthermore, the process occurs in smelting furnaces fueled by sustained and intensive heat currently generated mostly by fossil fuel–produced electricity.
At the other end of the life cycle, solar panels contain numerous potentially toxic materials that create hazards for landfills or require expensive and energy-intensive steps to recycle. Finally, the world’s dominant provider of solar technology, China, produces most of its cells using coal-burning furnaces on a grand scale.
These issues present a contradiction, making solar a source of clean power that is far from clean throughout the entirety of its life cycle. How the industry addresses these issues may determine how green its electricity generation can actually become.
Why Are Solar Cells Dirty?
All solar cells require routine cleaning to remove grime and dust so they can capture the rays of the sun and convert that energy to the electrons that constitute electricity. Unfortunately, the manufacturing process for PV cells is not so easily cleansed.
Dr. Lars Schernikau is an energy economist and a visiting fellow at the National Center for Energy Analytics in Washington, DC. He is also the author of The Unpopular Truth ... About Electricity and the Future of Energy. He emphasizes that the dirty side of solar panels is often overlooked and largely unavoidable.
“The idea that solar is carbon free or green is not correct,” he told The Earth & I.
“The idea that solar is carbon free or green is not correct.”
This contradiction within the life cycle of solar panels is largely attributable to the essential role of various carbon-based materials in the manufacturing process, most notably coal. “There is not one single solar cell possible without coal,” Schernikau added.
To understand this essential truth requires a return to some basic principles of chemistry. A solar panel converts sunlight to electricity using a thin layer of silicon, which is number 14 on the periodic table of elements, with the symbol Si. This abundant natural material is, unfortunately, not available in a free or independent state. It is almost always found bonded with other elements.
Releasing silicon from its tight chemical bond with oxygen requires an elaborate process that involves a heat-induced chemical reaction. This is a carbon-intensive process for a couple of reasons.
Typically, silicon is found in nature bonded with oxygen as quartz or quartz sand (silicon dioxide or SiO2). To extract pure silicon, the quartz is first melted in an electric arc furnace. Then other ingredients are introduced into the furnace to trigger the chemical separation. These are referred to as “reductive agents” and include a combination of wood chips, charcoal, coke, and coal. The common denominator in these items is carbon (a chemical element with the symbol C).
During the process, the carbon (C) in the reductive agents bonds with the oxygen (O2) in the quartz, separating out the pure silicon, Si. Yet, as the carbon strips away the oxygen, it forms a hazardous by-product: carbon monoxide (CO). Much of the CO then reacts with oxygen in the atmosphere to produce carbon dioxide (CO2). Both CO and CO2 are well-known greenhouse gases.
Furthermore, the intense heat used to power the furnaces and sustain the chemical reaction is almost always created by electricity that is generated from fossil fuels. This is largely because fossil fuel–generated electricity has historically been the most available source capable of delivering the extremely high‑power, uninterrupted electricity required to keep a silicon furnace at 1,700–2,000°C (3,100–3,600°F) weeks or months at a time. The key here is grid stability and sustained power.
Solar Panels’ ‘End of Life’
The other end of silicon’s life cycle is also dirty, although in a different way.
Solar panels do not have an endless lifespan. Historically, they have lasted for about 20 years. While the technology has improved—with panels installed more recently being more durable and lasting up to 35 years—the problem of waste remains.
Regardless of their duration, the so-called “end of life” for solar panels is an important phase that must be managed. While the toxicity of silicon is not a primary concern, other metals in the panels may be harmful if not disposed of properly. These can include cadmium, selenium, silver, and tin, depending on the panels and how they are constructed. In some cases, panels also include trace amounts of lead for electrical connections and conductivity.
Most decommissioned panels currently end up in landfills because recycling costs an average of $28 per module, whereas landfilling averages only $1.38.
Most decommissioned panels currently end up in landfills because recycling costs an average of $28 per module, whereas landfilling averages only $1.38. This economic disparity is driven by the technical complexity of separating tightly bonded materials like glass, silicon, and metals, which requires energy-intensive processes.
With a deluge of solar panels reaching their end of life within the next 20 years, without proper management the world could face 80 million metric tons of solar waste by 2050, overwhelming existing waste infrastructure.
Chinese Solar Power and Coal
When considering the dirtier side of solar panels, the role of China cannot be overlooked. According to the International Energy Administration (IEA), “China remains by far the largest producer of solar PV modules and components in the world.” In recent years, it has supplied 80% of the world’s solar modules and 90% of the silicon wafers that go into these modules. Thus, while the country is the world-leading contributor of hardware for producing green, renewable solar energy, its responsibility for the dirty side of solar tech is equally great.
Indeed, the process for manufacturing solar panels in China is actually compounded by a heavy reliance on coal in the specific provinces of China where most of the world’s PV panels are manufactured.
The IEA reports that global solar PV manufacturing gets about 60% of its electricity from coal. This number is significantly higher than the share of electricity the world gets from coal for all purposes, currently only 36%. The IEA attributes this divergence to two provinces in China, Xinjiang and Jiangsu, where the country’s PV production is concentrated and where coal accounts for more than 75% of the annual power supply.
If society wants to make solar completely green, it will have to address these weak spots in the technology’s life cycle, and China, more than any other country, will have to address its role.
The numbers don’t lie. If society wants to make solar completely green, it will have to address these weak spots in the technology’s life cycle, and China, more than any other country, will have to address its role.
Solar’s Promise Still Shines
Despite these unsettling realities, there is good news to report.
First of all, the problem may not be as bad as it seems in light of all the clean energy that solar panels generate over their operational lives. Prof. Vasilis Fthenakis, an adjunct professor and the founding director of the Center for Life Cycle Analysis at Columbia University, told The Earth & I that the emissions generated in the manufacturing of solar panels are tiny compared to the pollution from the fossil fuels that solar power replaces.
In other words, solar panels generate electricity from the sun with almost zero emissions throughout their lifespan of 20–35 years. Even when we add up the emissions from building the panels, the professor said, that total is still far less than what a coal or natural gas plant of the same size would release over those same years. Fthenakis added that when it comes to carbon footprint, solar panels “are the lowest among all electricity-generating technologies.”
Another way to understand the potential of solar panels to offset carbon emissions is to look at the concept of “net zero.” Simply defined, this refers to a balancing, or canceling out, of emissions. When a technology removes or eliminates the same amount of emissions it has generated, it has achieved net zero.
Annick Anctil, an associate professor of civil and environmental engineering at Michigan State University, told The Earth & I that solar panels can achieve net zero, and that they do so “very quickly.”
“The carbon payback time, which is the time it takes to pay back the carbon emitted during manufacturing, is usually one to two years,” Anctil noted. “This is very short, considering solar modules are designed for 25 to 30 years operation.”
Furthermore, the environmental impact is even less alarming at the disposal phase.
A study conducted by the IEA in 2020, entitled Human Health Risk Assessment Methods for PV Part 3: Module Disposal Risks, found that the health risk from solar panel disposal is minimal. Even in a supposed worst-case scenario, in which panels are disposed of in “nonsanitary landfills”—defined as landfills that do not have standard protections, such as leachate protection, groundwater monitoring, or liners—the risks of human exposure to cancer-causing elements and other toxic chemicals is “several orders of magnitude below” the maximum required by the US Environmental Protection Agency. The report also noted that solar panels “are unlikely to be disposed of in this manner.”
A More Efficient Solar Is a Greener Solar
While the environmental harm caused by solar panels may not be as bad as imagined, advancements in the technology are diminishing the harm even more. As panels become more efficient, the relative impact of emissions in the manufacturing phase decreases.
Furthermore, a grid that is increasingly powered by clean, renewable energy means that the emissions generated in the silicon manufacturing phase increasingly approach net zero.
Fthenakis, of Columbia, confirms this, noting that “emissions per unit of electricity generation are continuously lowered as PV module efficiencies increase.”
Encouragingly, some of this change is visible even in China, where so much of the emissions from solar cell manufacturing originate. The nation is also greening its own power grid.
However, it should be noted that China is also adding a record amount of new coal-fired power to maintain its grid stability, although generation from coal has declined. But Beijing's expansion of renewables does offer a positive prognosis for the greening of the country’s solar manufacturing industry. Fthenakis notes that “the sustainability of PV life cycles in China is improving as they introduce more PV to their grids.”
Ultimately, if coal can be systematically replaced in the high-heat manufacturing process—in China and across the globe—the environmental debt of solar power will shrink toward zero, allowing clean energy to finally live up to its pure, green promise.
*Rick Laezman is a freelance writer in Los Angeles, California, US. He has a passion for energy efficiency and innovation. He has covered renewable power and other related subjects for over 10 years.
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