What Is the Carbon Footprint of a Solar Panel? Overview and Emissions

We know solar panels are considered clean, but exactly how clean?

Solar panels on a grassy hillside with a fossil fuel power plant and a single wind turbine in the background

chris-mueller / Getty Images

We know solar panels are considered clean and green, but exactly how clean are they?

While at certain points in their lifecycle solar panels are responsible for carbon emissions compared to other renewable energy sources, it’s still a fraction of the emissions produced by fossil fuels like natural gas and coal. Here, we take a look at the carbon footprint of solar panels.

Calculating Carbon Footprint

Unlike fossil fuels, solar panels don’t produce emissions while generating energy—that’s why they are such an important component of the clean energy transition now underway to slash overall greenhouse gas emissions and slow climate change. 

However, the production steps leading up to that solar energy generation do cause emissions, from the mining of metals and rare earth minerals to the panel production process to the transport of raw materials and finished panels. When determining the net carbon footprint of solar panels, it’s therefore necessary to consider several factors, including how the materials used to produce the panels are obtained, how the panels are manufactured, and the anticipated lifespan of the panel. 

Mining Materials

Silicon is a chemical element used in chips, building material and industry. Platinum rough stone, industrial use.
Silicon is mined for solar panel production. RHJ / Getty Images

The basic component of a solar panel is the solar cell, usually made of silicon semiconductors that capture and convert the sun’s heat into usable energy. These consist of positive and negative silicon layers that absorb sunlight and produce an electric current by moving electrons between the positive and negative layers of the solar cell. This current is sent through a solar panel’s conductive metal grid lines. Each solar cell is also coated in a substance that prevents reflection so that the panels will absorb maximum sunlight. 

In addition to silicon, solar panels also use rare earth and precious metals like silver, copper, indium, tellurium, and—for solar battery storage—lithium. Mining all these substances produces greenhouse gas emissions and can contaminate the air, soil, and water.

It’s difficult to quantify those emissions because transparency varies when it comes to measuring and reporting the carbon footprint associated with extracting, processing, and transport of critical minerals and metals. A group of research centers has formed the Coalition on Materials Research Transparency to try to address this by developing industry-wide standards for evaluating carbon emissions from mining. So far, though, that work remains in its early stages. 

Types of Solar Panels

There is more than one type of solar panel, and different panels have different carbon footprints. The two types of commercial solar panels today are monocrystalline and polycrystalline—both made of silicon cells, but produced differently. According to the Department of Energy, these solar modules demonstrate energy conversion efficiencies ranging from 18% to 22%.

Monocrystalline cells are made from a single piece of silicon cut into small, thin wafers and attached to the panel. These are the most common, and have the highest efficiency. However, due to the complex process involved in making single silicon crystals, these produce the highest emissions. Polycrystalline solar cells, on the other hand, involve melting silicon crystals together, which requires less energy and thus produces less emissions.

Thin-film solar is a third technology that can employ one of several materials, including cadmium telluride, a type of silicon, or copper indium gallium selenide (CIGS) to generate electricity. But so far, thin-film panels lack the efficiency of their crystalline silicon counterparts. 

Emerging solar technologies seek to increase solar PV efficiency still further. One of the most promising new PV solar technologies in development today involves a material called perovskite. The structure of perovskite crystals is very effective at absorbing sunlight, and better than silicon at absorbing solar light indoors and on overcast days. Thin films made from perovskite may lead to panels with greater efficiency and versatility; they can even be painted on buildings and other surfaces.

Most importantly, there’s potential for perovskites to be manufactured at a fraction of the cost of silicon, and using far less energy.

Manufacturing and Transportation

Interior of a industrial warehouse with solar panels elevated on stands located on shop floor.

alvarez/ Getty Images

At present, however, silicon crystalline panels are the most common: In 2017, they represented about 97% of the U.S. solar PV market, and the vast majority of the global market as well. However, the manufacturing process for silicon panels produces considerable emissions. While silicon itself is abundant, it has to be melted in an electric furnace at extremely high temperatures before it is applied to the panel. That process often relies on energy from fossil fuels, especially coal.

Skeptics point to the use of fossil fuels in silicon production as evidence that solar panels don’t reduce carbon emissions all that much—but that isn't the case. Although silicon represents an energy-intensive part of the solar panel production process, the emissions produced are nowhere near those of fossil fuel energy sources. 

Another consideration revolves around where solar panels are produced. Silicon panel production in China has grown considerably in the past two decades. In China, about half the energy used in that process now comes from coal—considerably more than in Europe and the United States.This has raised concerns about the emissions associated with PV panels as manufacturing increasingly concentrates in China. 

Emissions from transportation present another challenge. The mining of raw materials often takes place far from manufacturing facilities, which in turn may be continents and oceans away from the site of installation. 

A 2014 study by the Argonne National Laboratory and Northwestern University found that a silicon solar panel made in China and installed in Europe would have double the carbon footprint compared to one that was both manufactured and installed in Europe, due to China’s larger carbon footprint from the energy sources used in manufacturing along with the emissions footprint associated with shipping finished solar panels such a long distance. 

But researchers say that the emissions gap between China and other major manufacturing sites could decrease over time if China adopts more stringent environmental regulations as part of its emissions reduction commitments. There’s also a push to expand the PV supply chain and production domestically in the U.S., E.U., and elsewhere, which would reduce reliance on China.

Lifespan of a Panel

The lifespan of a solar panel is another important factor in determining its carbon footprint. The solar industry typically guarantees that panels will last between 25 and 30 years, while the energy payback time—the time it takes for a panel to pay back its “carbon debt” from emissions created during extraction, manufacturing, and transport—is generally between one and three years depending on factors like location and the amount of sunlight it receives. That means a panel can usually generate carbon-free electricity for decades after that brief payback period. 

And although older solar panels definitely lose efficiency with time, they can still generate a significant amount of energy for years beyond their warranty. A 2012 study by the National Renewable Energy Laboratory found that a solar panel’s energy output rate typically declines by just 0.5% per year. 

Measuring a solar panel’s carbon footprint over its lifespan must also consider how it's disposed of at the end of its productive life—and whether some solar panels are removed prematurely. 

A recent study from Australia found that the latter is frequently the case, with many incentives to replace panels before they reach the end of their productive life. The authors cite a combination of government incentives that encourage the installation of newer panels and a tendency for solar companies to deal with a damaged panel by simply replacing the entire PV system. In addition, people often want to swap their systems after just a few years of use for newer, more efficient systems that offer greater energy savings. The consequence for Australia is an alarming growth in e-waste from discarded solar panels.

Recycling offers a partial solution to the problem of disposal, but it has the potential to increase the carbon footprint when discarded panels must be transported long distances to recycling facilities. The study authors concluded that extending the life of solar panels is essential to solving the emissions and waste challenges associated with end-of-life panel disposal.

Solar Panels vs. Standard Electricity

A solar energy systems engineer of African descent wearing safety goggles and white hardhat performs an analysis of solar panel energy efficiency.

wera Rodsawang / Getty Images

While there’s no denying that solar panels have a carbon footprint, it still doesn’t hold a candle to the carbon emissions and other environmental impacts that come from electricity generated by fossil fuels. 

A 2017 study published in Nature Energy conducted life cycle assessments of renewable and non-renewable energy sources and found that solar, wind, and nuclear all have carbon footprints many times lower than fossil fuel-generated energy. That was true even when accounting for “hidden” emissions sources like resource extraction, transportation, and production—which, of course, are also associated with fossil fuels. The study found that coal, even with carbon capture and storage (CCS) technology deployed, generates 18 times the carbon footprint of solar over its lifetime, while natural gas has 13 times the emissions footprint of solar. 

Over time, solar panel production has gotten more efficient, and ongoing research and development constantly seeks to increase efficiency while lowering costs and emissions. 

How Much Better Is Solar for the Environment?

Carbon emissions are just one significant factor in assessing the environmental impacts of solar panels. While the generation of solar energy itself is non-polluting, solar relies on non-renewable metals and minerals. This involves polluting mining operations and often results in habitat and biodiversity loss as mines and roads are constructed through pristine areas to facilitate transport of equipment and raw materials. 

Just as with any form of energy generation, some people will experience greater adverse impacts than others—for example, those living in close proximity to mining operations or panel manufacturing facilities that burn fossil fuels. And there are additional impacts associated with e-waste from discarded panels. 

However, when we consider the total environmental impact of solar panels versus energy generated from fossil fuel sources, it’s no contest: Solar has a much, much more limited impact in terms of carbon emissions and pollution. Nonetheless, as the world transitions to low-carbon energy sources, it will be important to continually improve standards and practices aimed at minimizing impacts while distributing unavoidable environmental burdens in more equitable ways.

Key Takeaways

  • Solar panels don’t produce emissions while generating electricity, but they still have a carbon footprint. 
  • Mining and transport of materials used in solar panel production and the manufacturing process represent the most significant sources of emissions. 
  • Nonetheless, the carbon footprint of a solar panel during its entire lifecycle is many times less than the carbon footprint of fossil fuel-based energy sources.
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