Coal’s importance for SOLAR PANEL MANUFACTURING

Coal is not the favorite "Child" these days.

Not only have the United Nations and the IEA literally declared "War" on coal, but countless political, activist organizations and even leading financial institutions have pledged, if it had to be in their power, to immediately stop the usage of coal.

Today's blog is not about globally measured temperature changes, its causes and its negative or positive impacts, but about coal and solar.

So why are coal and solar so closely interlinked? Why is it that solar panel manufacturing is impossible without coal? I always thought that coal is "Only" important for electricity, contributing to 36% of global power demand, or over 8h of 24h every single day of the year.

I always thought that coal is "Only" required to produce all steel.

Let us have a look at solar panel manufacturing, which is really about silicon production.

Obviously, this power comes from coal in China, and cannot come from wind or solar.

6N pure silicon means 99.9999% purity level, 11N pure silicon means 99.999999999% purity level, you get the point.

Metallurgical-grade silicon making and high purity quartz Elemental silicon is not a naturally available element.

All simplified Iron making: Fe2O3 3C heat => 2Fe 3CO Silicon making: SiO2 2C heat => Si 2CO This means that each ton of silicon roughly releases 5-6 tons of CO2 in this silicon smelting process alone.

Carbon sources for silicon making: Coal, petcoke, hardwood Interesting is that various sources of carbon are used for the silicon smelting process.

For more detail on silicon smelting please also see Troszak's 2019, Burning coal and trees to make solar panels.

Shredded hardwood must be mixed into the silicon smelter "Pot" to allow the reactive gasses to circulate, so that the liquid silicon that forms, can settle to the bottom for tapping, and to allow the resulting CO to escape the smelter "Charge" safely.

Metallurgical grade silicon from the smelter, usually of 98% purity, does not meet the purity requirements of the photovoltaic industry, it must undergo two more energy-intensive processes before it can be made into solar cells and then into panels.

Firstly, the Siemens Process converts metallurgical grade silicon from the smelter into polycrystalline silicon by using an extremely energy intensive process, a high-temperature vapor deposition process.

The purity requirement for solar grade silicon is currently 9-11N, a factor of 10.000 to 100.000 more pure compared to the 5-6N purity required for solar PV a decade ago and likely the basis for the solar panels on your roof.

Secondly, the Czochralski Process turns the liquid silicon metal from the smelter and doping materials into the silicon ingot, a large monocrystal, 20-30 cm diameter and 1-2 m in length.

Solar grade silicon is the most energy-intensive step in the silicon purification process and should best be understood. 

https://unpopular-truth.com/2024/05/09/coals-importance-for-solar-panel-manufacturing/