What are the carbon emissions for manufacturing solar panels and wind turbines?
Renewable energy sources, such as the sun and wind, are often presented as the best way to reduce our carbon footprint, the greenhouse gas emissions that cause climate change.
But are there emissions associated with renewable energy? The quick answer is yes, but based on current estimates, these emissions appear to be much lower than if fossil fuels (coal, gas and oil) were used to produce that energy.
Still, it is important to know the emissions involved in their production and use, such as those from the manufacture of solar panels and wind generators.
Emissions from the manufacture of photovoltaic solar panels
Unlike fossil fuels, solar panels produce no emissions while generating energy, which is why they are such an important component of the clean energy transition.
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However, the production steps leading up to solar power generation do cause emissions, from the mining of metals and rare earth minerals to the process of producing the panels and transporting the raw materials and finished panels.
Solar panels require a complex manufacturing process involving the use of chemicals, heat and electricity to produce photovoltaic cells made of silicon, a material that melts at 1,414°C (1,414°F).
This process releases a number of pollutants into the atmosphere such as nitrogen oxides (NOx), sulfur dioxide (SO2), carbon monoxide (CO), volatile organic compounds (VOCs) and particulate matter (PM).
In addition to silicon, solar panels use rare earths and precious metals such as silver, copper, indium, tellurium and, for solar battery storage, lithium.
The extraction of all these substances produces greenhouse gas emissions and can pollute the air, soil and water. Although there have been technological improvements that have reduced these emissions over time, they are still of concern.
There are two main types of photovoltaic cells. Monocrystalline cells are made from a single piece of silicon cut into small, thin wafers. They are the most common and have the highest efficiency.
However, due to the difficulty in manufacturing individual silicon crystals, they produce the most emissions. Polycrystalline solar cells, on the other hand, involve the fusion of several silicon crystals, which requires less energy and therefore produces fewer emissions.
Taking this into account, on average, during the first years of operation of these panels, the equivalent of about 50 g of CO2 per kilowatt-hour is produced. This is 20 times less than the emissions per kilowatt-hour of coal.
The panels must be in operation for at least three years to offset their carbon footprint, which is not a problem since their lifetime is more than 20 years.
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This footprint of solar panels is set to be further reduced with the incorporation of new types, such as thin-film cells, and a material called perovskite that could become twice as efficient as silicon. This material could even be painted on building facades and other surfaces.
The carbon footprint of wind turbines
The manufacture of the huge wind turbines that are now part of the landscape in many parts of the world, although not as technologically complex as silicon, involves some emission of polluting gases into the atmosphere.
The main source of emissions is from the burning of fossil fuels during the manufacturing process of these huge steel and fiberglass structures. The process releases NOx, CO2 and particulates, and in addition, some components require rare earths, such as neodymium, which are scarce and difficult to extract.
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However, despite these drawbacks, wind turbines are even cleaner than solar panels. Measured equivalent emissions range from 5 grams per kilowatt-hour in the USA to 25 grams measured in China, i.e. up to 200 times less than coal.
This means that a wind turbine can pay off the carbon debt of its manufacture in as little as seven months. As with solar panels, wind turbines produce no emissions once they are in operation.
There are a multitude of sources and studies to arrive at these figures, which complicates their evaluation. An organization called COMET (Coalition for Materials Emissions Transparency), aims to find a unified way of calculating greenhouse gases for all industrial mineral supply and process chains.
In any case, the data are clear: wind and solar are alternatives that generate far fewer greenhouse gas emissions. The switch to these clean energies must happen as soon as possible worldwide.
