Climber99, #28: "Even if "renewables" were to go through 4 doubling from 4.5 to 9 to 18 to 36 to 72 kWh/day per person (which is highly unlikely in my view), it would still mean the average American would have to reduce their energy consumption by 71% (from 250 to 72 kWh/day). Forget running an electric car! However it gets worse than this because not all the 72 kWh/day would be available to people. A proportion (perhaps all) of this 72kWh/day will have to be reserved to "renew" the "renewables" as they come to the end of their life spans."
Each doubling of wind and solar should take at most 4 years at current rates of growth (see below): I am figuring an average of 20% per year, which is a conservative medium between the 17% per year and 37% per year mentioned below for wind and solar, respectively. At 20% per year, doubling takes about 3.5 years. Four years, then, is a conservative estimate. Hence, four doublings should take ~15 years, from now to about 2030. Of course, there will still be room for more doublings, and by then the momentum is likely to be even greater since there are feed-forward effects of high volume, at least to a point (i.e. to a point somewhere shy of complete saturation). Remember the exponential function, a la Al Bartlett. Solar PV growth has proven to be explosive, exceeding everyone's expectations. Solar is kicking nuclear's ass since it is so cheap and easy to install, and getting cheaper all the time.
Quite possible that we could be at 100% renewables by mid-century or before, based on conservative current growth rate extrapolation. Also, that assumes the existing subsidy structure, which heavily favors non-renewables, and it also assumes that the fossil fuel industry will continue to put up stiff resistance. Renewables are winning, even though they are charging into that headwind. If the subsidy structure were changed to even things out, or to favor renewables, and if the FF industry could be shut up, then it could happen a lot quicker.
It is amazing that this growth is happening, and will happen, just on economics alone – i.e. the economic advantages of renewables even in the face of the subsidy headwind. In other words, it is happening mostly because it is a sensible business/financial decision, rather than because of climate concerns or whatnot. Political efforts to speed things up would be nice, but may not be necessary. Saying this goes against my grain: I have a latent dislike for the idea of the world being saved as a business decision – as a side-effect of an ROI calculation. And yet, there it is. That's how things are unfolding, whether I like it or not. And at the end of the day – ideology be damned – I'll take it. And maybe I can learn to LIKE it. 
Mark Jacobson seems to think that lack political will is an important impediment, but I am not so sure. It seems that it is happening just on economics alone; the statistics on explosive renewables growth don't lie, even if politicians do.
For background see here: https://en.wikipedia.org/wiki/100%25_renewable_energy
Dramatically reduced pollution and CO2 release (with all that those imply for health, cost savings and planetary sustainability) will be "side effects" of the conversion.
As for "renewing the renewables" (i.e. replacement at end of life-cycle): no problem. Life cycles now appear to be at least 30 years and in most situations a half-century. The problem by then will be OVERcapacity, since vast new production structure will have been built up during the rapid-doubling years; this is happening right now, in fact. The big renewables build-out will be a one-off thing, with only a trickle thereafter required for maintenance/replacement. We will have cheap energy from super high-EROI renewables requiring little maintenance and only multi-generational replacement (i.e. your grandkids will likely still be getting plenty of cheap energy – minus a half-percent or so attritional annual loss – from the PV panels you installed 40 years earlier).
The world is a strange darn place.
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http://www.afp.com/en/news/renewables-posted-record-growth-rate-2015-irena … Renewables posted record growth rate in 2015: IRENA … 07 Apr 2016 … snip … "Wind power capacity grew by 17 percent, or 63 GW, "driven by declines in onshore turbine prices of up to 45 percent since 2010," said the report. Solar power capacity rose by 37 percent, or 47 GW, after prices of solar modules fell. However, hydropower capacity increased only by three percent, while bioenergy and geothermal energy capacity increased by five percent each."
