> Yes, but today we’re using coal to produce solar panels. Why even bother with such a fantasy hypothetical? Why not just go all the way to cold fusion if we’re just making stuff up that isn’t being done currently?
One obvious difference – the technology to capture waste CO2 gas is clearly feasible in principle. We already have lots of research into capturing and reusing CO2 (such as from coal-fired power stations) [1], and we already have known industrial processes which use CO2 as input [2]. So, the issue here is really (a) more R&D to finesse the technology, (b) its application to silicon refining specifically (other CO2 emissions sources are more significant and hence receive more focus) (c) getting the economics right. (On the last point, emissions trading schemes may help.) By contrast, most of the physics community doesn't believe cold fusion is a real phenomena, and the small minority who think it is can't explain how it works. You are comparing a technology whose physics and chemistry is well understood, and which basically just needs productisation, with a technology where there is disagreement on whether physics even allows it to exist.
[3] seems a particularly interesting approach - conversion of CO2 gas to graphite. The graphite in turn could potentially be reused in the silicon refining (which needs a carbon source, not coal/coke/wood specifically). Most current methods of procesing CO2 turn it into chemicals such as methanol (CO2 + hydrogen gas), urea (CO2 + ammonia), etc, which while useful, I'm not sure you could actually reuse those chemicals in silicon refining
[1] https://en.wikipedia.org/wiki/Carbon_capture_and_storage
[2] e.g. https://en.wikipedia.org/wiki/Methanol#From_synthesis_gas
[3] https://www.nature.com/articles/s41467-019-08824-8
> This is what I meant about the left having a fantasy that one day technology will save us
I'm not sure it is really "the left having a fantasy". I know plenty of right-leaning people with solar panels on their roofs. (I even know global warming sceptics with solar panels on their roof.)