Clean coal must be the only way forward in the near term, but there is no clear plan.  There is a lot of vehemence about renewables replacing coal, so first we need to do a reality check.

We can't do without coal for electricity, because it provides the base load power which reliably keeps the lights on.  Renewables are intermittent, therefore unreliable, and can't be used for more than 20% of grid power.

Anything more than that 20% must be wasted unless some form of battery storage for excess renewable energy can be found.  That's still a dream.  So what about hydrogen instead of batteries?  We haven't heard much about the "hydrogen highway" recently, because it's a road to nowhere. Hydrogen has big, apparently insuperable, problems of storage and transport, and the fuel cells which could use hydrogen in cars are not feasible, despite lots of research.  See Joe Romm's excellent recent book, The Hype About Hydrogen.

Given that we're stuck with coal, at least for the near term, we must urgently seek a solution for its emissions.  Carbon dioxide (CO2) in the flue gas from coal-fired power plants first must be captured somehow, then disposed of.

The capture problem, for post-combustion flue gas, is still not solved.  Amine scrubbing, a chemical approach, is the only alternative being studied by DOE, but this chemical approach is overwhelmed by the large nitrogen ballast (75% of the volume of flue gas is harmless N2) and plagued by precipitation and coal ash.  And it's very, very expensive.

Disposal of CO2, during the Bush years, was assumed to mean some sort of dumping underground or in the ocean, a solution called "sequestration."  But the GAO has recently issued a report critical of the DOE's reliance on sequestration, pointing out the political and technological obstacles to storage of lethal gas under where we live.  So if the usual American solution of dumping doesn't work, what's left?

Only recycling, by cracking.  Cracking is the electrolytic decomposition of CO2, breaking it into CO and oxygen.  This takes a lot of energy, 5.5 electron-volts (5.5 eV) per molecule cracked, or 531.4 kJ/mol.  Cracking a ton of CO2 requires 12.08 GJ and the internal energy is 0.68 GJ/ton for flue gas CO2, so 11.4 GJ/ton is the net energy input required for cracking a ton of coal plant carbon dioxide.

Using any fossil fuel to provide the required cracking energy (11.4 GJ/ton, 1 MWh = 3.6 GJ) creates more CO2 than is cracked, so some other energy source must be found.

Wind and solar (renewables) could provide the cracking energy for clean coal.  The CO2 could be stored on site awaiting availability of renewables, or transported in pipelines to where renewables are abundant.  Besides dealing with the global climate change problem, cracking coal CO2 by renewable energy also recycles oxygen back to the plant and produces valuable solid carbon as a byproduct.  The profit from the recovered cracking byproducts might induce polluters to reduce CO2 emissions

There is also a process recently discovered by the Idaho National Lab called "syntrolysis" -- the simultaneous cracking of CO2 and water to make syngas (carbon monoxide mixed with hydrogen gas), which can be made by well-known procedures into liquid vehicle fuel.  Water electrolysis takes approximately as much energy per molecule as CO2 cracking.

Hybrid power would marry coal and renewables, providing the reliability of coal and the low emissions of renewables, using the best features of each to offset the worst features of the other.  An odd couple indeed, but apparently the only hope to prevent global climate change.  The challenge now becomes political, to calm down the radicals on each side who stand in the way of a successful marriage.

For more information, check out http://www.vorsana.com.