Justin Richards wrote:
>> would do this by adjusting the valve that feeds water down the
>> tunnel to
>
> Intuitively, this would have issues dealling with sudden demand
> changes.  Perhaps the majority of these system upsets are small
> compared with the overall system capacity.

Some types of hydro plants are actually reasonably fast adjusting to demand=
,
on the order of 10s of seconds.  Nukes take much longer than that, and
therefore generally provide the baseline power.

The current standard has the regional control authority sending requests fo=
r
power every 4 seconds.  The generally slow response of most electricity
generation is one reason having short term fast responding systems on the
grid makes sense.  These guys make large 100KWH flywheels with the
electronics to quickly store or retrieve power:
http://www.beaconpower.com/products/about-flywheels.asp

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