Eli has been thinking about clean coal. Not being an absolutist, the bunny will gladly settle for half a carrot (or even a third, below that we can negotiate), and his idle thoughts went along the following track. . . Coal gasification is an interesting technology, certainly an old one with town gas being around for going on 200 years. You start by burning coal
C(s) + O2(g) --> CO2(g), ΔH0 = -394 kJ/mole
The - means that that much energy is released per mole of carbon burned. Coal is mostly carbon. If you keep the oxygen availability low the CO2 reacts with hot coal to give
CO2(g) + C(s) --> 2CO(g), ΔH0 = +172 kJ/mole
so you get carbon monoxide and now you add superheated steam to the system
C(g) + H2O(g) <--> CO(g) + H2(g), ΔH0 = +131 kJ/mole
You can also play with the water gas shift reaction
CO(g) + H2O(g) --> CO2(g) + H2(g) ΔH0 = -41 kJ/mole
usually using some catalyst to produce more hydrogen or you can drive coal gasification at high pressure by
C + 2H2 <--> CH4, ΔH0 = -75 kJ/mole or
CO + 3H2 <--> CH4 + H2O(g), ΔH0 = -206 kJ/mole
Town gas has a varied composition depending on how the process was tuned (temperatures, pressure, etc. Typically 50% H2, 35% methane, 10% CO and 5% ethylene, but pretty much any variation is possible depending on end use. The CO is why old movies have people killing themselves by doing a turkey imitation and sticking their heads into an oven. It doesn't work real well with natural gas, although you can blow your house up by leaving the gas full on for a couple of hours and lighting a match.
But to get to the point, combining a concentrating solar power plant with a coal mine, or come to think about it an oil shale or tar sand extraction facility might be a viable way to get to lower carbon emissions for producing liquid fuels and chemicals. If nothing else we need lots of hydrocarbons for the chemical industry. While the net energy output would be lower than from separate coal + solar electricity generation (there will be inefficiencies), it could be greater than either separately and the CO2 emissions would be lower than from a coal burning plant alone. In other words, this is a strategy for less polluting coal, not clean coal. We talked about that earlier.
Now this is but an idle thought, and whether it is worth anything depends on the details, but let Eli throw it out their for others to chew on. He suspects others have thought about this too and would appreciate if somebunny pointed it out