Time is against the fossil fuels, as each barrel burned makes the next barrel harder to get and more expensive, while with the renewables, each megawatt produced makes the next megawatt easier to produce.

Only up to some point.

Just as fundamental geology limits oil production, fundamental physics limits practicalities of full renewables. It's unfortunate it is so, but it's truth.

The magnitude of renewables, except large-scale hydroelectric, is still so much less because of the much lower energy density of the input. There is no way to engineer around that immutable fact.

Consider 2.5 MW wind turbines---the biggest on-land ones, these give power-factor adjusted at best 1MW. Fifty of these on a ridge are very impressive, and noticable---drive by such a wind farm. You can see a large capital investment, and for some people quite an undesriable alteration to the landscape. And yet, this is nothing---you need at least 1000 to equal the useful electrical output of one single nuclear reactor. One thousand, to put where? And for but small increment to capacity? Modern nuclear plants have two or three reactors, as well.

Significant scale-up of nuclear seems quite difficult, but equivalent scaleup of PV and wind seems substantially further from practicality. But when people see the large numbers for PV and wind (so far from current) the dreamy optimism takes over---like for a caveman going to alpha centauri is not much harder than going to the moon. But, it really is.

How many megawatts of clean, truly home made and renewable power would 20 trillion dollars buy? Any guesses from the math and stat geeks out there? :-)

A heckuva alot less than the same invested in coal and nuclear. Coal will be cheapest for a very long time, but I think we ought to forbid it anyway.