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To decarbonize heavy industry, highly concentrated solar thermal is the best option. Heat is the form of energy most responsible for carbon emissions in industries like steel and cement. Solar thermal (duh) generates heat from thousands of "suns" of sunlight.

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Solar may replace the heat component in some applications (as in this one), but in refining steel the carbon is required for the chemical process - it binds the oxygen from the iron. Carbon in that application can be replaced by hydrogen, but it can’t be just replaced by another heat source.

How is that carbon emissions? It sounds like carbon absorbed?

> How is that carbon emissions?

In goes iron ore, a mix of iron oxides and carbon, out comes iron and carbon oxides. The carbon moved from the ore to the atmosphere.

So if I recall correctly from HS chem, iron is being reduced in this case by the carbon in the coke. From a cursory glance at the electronegativity table, iron is at 1.83, carbon's at 2.5 and hydrogen is 2.1. Higher electronegativity = more attractive to electrons = better reducing agent so hydrogen will reduce iron but less efficiently? than carbon. I don't know if this means that more energy is required to get the hydrogen to reduce carbon, or if the reaction will just be slower, but the upside is that the only byproduct of this process is pure H2O.

You push a lot of carbon into the iron, most react with oxygen and go away as CO2. So the entire process emits CO2, and absorb pure carbon (usually from oil).

You can reduce iron by electrolysis, where you vent oxygen instead of CO2 or water. You'll just need a higher temperature and some quite robust electrodes (both of what are currently expensive).

What you just can't do is replace the carbon that is added into the steel. The process will always need a carbon source.

CSP is way more efficient than photovoltaics, but electricity is much more flexible and easier to control than heat.

I'll not be surprised if the industry decides to waste 70% of the energy and go with photovoltaics.

That, or there will be an optimal mixture. Eg, CSP may be akin to baseload and you'd draw from the grid for the rest

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