nor do they specify the "need" for any percentage of "dependable" energy sources.
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They sure do specify the need for "dependable" energy sources:
http://www.nap.edu/openbook.php?record_id=12619&page=259
"Dispatchable resources, typically natural-gas-fired units and sometimes hydropower, and interruptible demand are used to compensate for the lack of dispatchable resources when scheduled wind or other capacity diminishes."
Evidently you don't know the vocabulary of the industry. In the electric power industry, a "dispatchable" power source is one that you have "at your command", in other words, it is "dependable". The "dispatchable" resource delivers power on command. Nuclear, gas, coal, hydro are all "dispatchable" resources since they can be commanded.
Wind / solar are not dispatchable. You can't command either wind nor solar to give you energy on command; they are held hostage to the whims of Mother Nature - they are "unreliable".
So when the power from the unreliable solar and unreliable wind decreases due to the whims of Mother Nature; the utility has to have enough extra capacity in the power sources it CAN command to compensate for the unreliability of the renewables.
It's really, really simple. I don't know why you continue to go through all these prevarications to attempt to turn a "sow's ear" into a "silk purse".
PamW