NREL has put out a report on alternative energy, among other things it purportedly says that 80% of US energy demand can be met by alternative energy sources by 2050.

EDIT: Should be US electricity demand

I'm looking into this now to see the details, but already I see severe assumptions being built in.

As always, the first thing I look at is projections of demand.

Here already there are major assumptions being made:

Electricity demand NREL 2010 2050.png
Here are the 3 scenarios outlined by the report: high demand, low demand, and EIA Waxman Markey Analysis.

This doesn't seem so bad, until you see what historical performance was like:

Electricity demand NREL 1970 2050.png

High demand, in other words, is what the US has been doing with respect to electricity consumption for literally decades.

In more specific terms:

Sector High-Demand Baseline Low-Demand Baseline
Residential 2% decline in intensity over 2010 levels 30% decline in intensity over 2010 levels
Commercial 5% increase in intensity over 2010 levels 32% decline in intensity over 2010 levels
Industrial 35% decline in intensity over 2010 levels 50% decline in intensity over 2010 levels
Transportation <3% plug-in hybrid electric vehicle (PHEV) penetration 40% of vehicle sales are plug-in electric vehicles (PEVs)
40% of vehicle sales are PEVs?! 30% to 50% decline in consumption across the board?

Seems like fantasy to me. And note that the above are all predicated under 2.4% annual GDP growth rates - another fantasy.

The 'Low Demand' curves also assume mass installation of all sorts of technologies with very high startup costs:

In that report, the installed cost per kilowatt across nine different installations ranged between $2,300 and $5,000 (with one outlier at more than $8,000). Field tests with the first generation of the second manufacturer’s system estimated an installed cost of approximately $2,500/kW (Horsey 2009).
Then, of course, the assumption is that by 2050 the cost will fall to almost nothing:

Table L-4 shows the cost assumptions corresponding to the steps of the cost curve for NERC region 1, represented by the Chicago location (as per Table L-3).64 The cost estimates are shown for even years, following the 2-year time interval used in ReEDS. While the cost of ice storage for new buildings is initially $2,200 in 2012, it falls to approximately $1,950 by 2020. Thus, over the next decade it is assumed that the target cost set by one of the manufacturers discussed in a previous section, Cost Estimates for Ice Storage Systems, is achieved. By 2050, the cost falls by another $150 per kilowatt.
To put this in perspective: under the high demand scenario (i.e. business as usual), hourly demand averages in the 450 Gigawatts to 600 Gigawatts, with peak up to 900 Gigawatts or so. The Low Demand scenario hourly demand averages 300 Gigawatts to 450 Gigawatts with peaks up to 700 Gigawatts or so.

To store the 250+ Gigawatts under the above thermal energy storage systems would cost only $700 billion or so today but only $49 billion by 2050. ($550 billion + 30% add on installation costs using assumed $2200 install cost vs. $37.5 billion + 30% add on using $150 install cost)

More to come...