For those not in the know, silica, or silicon dioxide, is sand. Silicon is 28.2% by weight of the earth's crust. The second most abundant element. And:

Energy payback times and carbon footprints range 0.68–1.96 years and 15.8–38.1 g CO2-eq/kWh (hydropower/UCTE electricity, 1700 kWh/m2 year). This is for various types of photovoltaic panels. Compare that with coal, which is 940 g CO2/kWh. Natural gas is about half that. So coal is about thirty times worse than photovoltaics and that does not include that produced in the manufacture of the coal powered power plant nor in the mining and shipping of the coal.

If you are interested the link is:
https://www.sciencedirect.com/science/article/pii/S0927024813004455

Where some of these ideas come from is beyond me. And now I think I will have a frozen yogurt and let people get back to trains.