The carbon footprint of silicon solar panels

Putting up huge numbers of solar panels every day could help address the world’s energy crisis. ‘If you want to solve big problems, then the scale of whatever you are doing is also likely to be big, and so is any waste you generate,’ explains Frederik Krebs who led a study at the Technical University of Denmark. ‘This should therefore be part of your thinking when you are developing something.’ [1]

solar powerAlmost 90% of the World’s photovoltaics today are based on some variation of silicon. Solar energy is an essential part of the global move toward clean, renewable energy, and it is critical that the growing solar photovoltaic industry is itself truly safe and sustainable.

Production of silicon-based solar PV panels begins with the mining of silica, found in the environment as sand or quartz. Silica is refined at high temperatures to remove the oxygen and produce metallurgical grade silicon. Higher purities are achieved through a chemical process that exposes metallurgical grade silicon to hydrochloric acid and copper to produce trichlorosilane gas … and waste silicon tetrachloride, an extremely toxic substance that can constitute an extreme environmental hazard. … The trichlorosilane is distilled (and then) heated or “reduced” with hydrogen to produce silane gas. The silane gas is heated again to make molten silicon, used to grow crystalline silicon (c-Si) .



The high temperatures required for c-Si production make it an extremely energy-intensive and expensive process, and also produces large amounts of waste. As much as 80% of the initial metallurgical grade silicon is lost in the process.


Furthermore, the extremely potent greenhouse gas sulfur hexafluoride is used to clean the reactors used in silicon production. The Intergovernmental Panel of Climate Change considers sulfur hexafluoride to be the most potent greenhouse gas per molecule; one ton of sulfur hexafluoride has a greenhouse effect equivalent to that of 25,000 tons of CO2. It can react with silicon to make silicon tetrafluoride and sulfur difluoride, or be reduced to tetrafluorosilane and sulfur dioxide. Sulfur dioxide releases can cause acid rain, so scrubbers are required to limit air emissions in facilities that use it. [2]

coal power


Silicon-based solar cells require a lot of energy input in the manufacturing process. The source of that energy, which is often coal, determines how large the cell’s carbon footprint is.


Varying regulations and manufacturing practices make it difficult to get standardized data about the environmental footprint of photovoltaic panels. A study released in May by Northwestern University and Argonne National Laboratory found that the carbon footprint of a panel from China is twice that of one from Europe, because China has fewer environmental standards and more coal-fired power plants.

The new ranking of 37 solar manufacturers, the Solar Scorecard created by the Silicon Valley Toxics Coalition (SVTC), shows that some companies are doing better than others. The SVTC hopes that pushing for more transparency now will lead to better practices later. If companies adopt sustainable practices – such as recycling – now,  then over the next 10 or 15 years, as older panels that come down are recycled – the new panels on the market could be zero waste.

Right now, solar panel recycling suffers from a chicken-or-egg problem: There aren’t enough places to recycle old solar panels, and there aren’t enough defunct solar panels to make recycling them economically attractive.[3]


In addition,  90% of crystalline silicon photovoltaic cells, which are the most common solar cell, use a silver paste [4] to reflect solar energy back into the cells to maximise energy production.


Silver is … a precious metal, cutting into both the cost of production and energy payback silver savedtime of mass-produced solar cells. It has been demonstrated that 95% of the silver electrodes in polymer solar cell modules can be reclaimed as silver chloride after simply shredding the modules and soaking them in nitric acid. This yield would diminish the overall energy payback time of the solar cells from 139 days to 128 days, a decrease of 8%. [1]

It is possible to create silicon based solar panels far more efficiently, cleanly and to recycle the materials used. There still is not nearly the awareness there should be that solar panels are not all created equal from an environmental standpoint. [3]


References:                                                                                                                             1. (January 3, 2014)

2. (September, 2013)

3. (November 11, 2014)

4. (August 29, 2014)



One thought on “The carbon footprint of silicon solar panels

  1. Pingback: The carbon footprint of silicon solar panels | mankind’s changing world | WORLD ORGANIC NEWS

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