Coal is clearly important. Our problem in the short term is that in the west, coal use is actually being cut down. Good for the environment but terribly risky.
For instance, in the UK we have a lot of coal burning power stations, they are all old and pollute like there's no tomorrow. In order for these to remain online, they are required by law to have particulate filters fitted.
The energy companies (of which I have insider information on one of Europes biggest) are planning to shut these power stations down (or at least mothball them) rather than fit expensive filters.
The replacement power generation will be partially "renewables" but mostly natural gas.
I don't think this situation is unique.
Therefore, to move towards coal to retain sufficent energy inputs to enable us to produce PV, Wind and Nuclear is going to require some years of planning and investment. Those years may be a luxury we cannot afford, especially if gas production hits a cliff.
I also wonder where the practical limit of coal extraction is. Each coal mine, whether they are underground or open cast must have a physical limit on how much coal can be removed at any one time. I doubt it's well understood what the limit may be or whether it's capable of dealing with a increase in demand with perhaps only months or a couple of years to adjust.
These increases in demand could be huge. One lb of coal = 16,000,000 joules and one lb of oil = 24,000,000 joules. Therefore, before even taking into account the energy required to turn coal into oil, we already need 50% more coal than oil to fulfill the same energy purpose.
That means, one barrel of oil contains about 254 lbs of oil. To replace one barrel of oil with coal requires 381 lbs of coal. So, to exchange a mere 10 million barrels a day of oil, will require 1,905,000 tons of coal - plus the energy to do the conversion process. That's 696 million tons per year or 14% of current coal production of around 5000 million tons per year. Not impossible, but very challenging - and that's to replace 12.5% of current oil demand. In this scenerio we'd need all the renewables we could get to power the conversion process too.
If we start talking about 20% or 30% of current oil consumption then we'd better start producing some more fuel efficent cars and fast!! A 30% drop in oil would equal around a 33% increase in coal production plus large amounts of renewables or nuclear power to balance the energy equation.
According to this report (
http://www.planetark.org/dailynewsstory ... /story.htm ) China is turning 13,000 tons of coal into 50,000 barrels of oil. 13,000 tons = 26,000,000 lbs. 50,000 barrels = 12,700,000 lbs. That's indicating that the process is actually so inefficent that they're only turning half the energy potential of the coal into oil. Therefore, the more accurate figures may be - 10 millon barrels of oil requires more like 920 million tons of coal or 18.4% of current coal production to replace 12.5% of current oil production. Whoops - looks like we'd better start building a lot of windmills, mini-hydros, PVs and nuclear plants and we'd better start on it fast!!
-- Energy potential refs: --
http://physics.syr.edu/courses/modules/ ... ables.html