Re: dams and electricity

[David Bowman <dbowman@TIGER.GEORGETOWNCOLLEGE.EDU>]

Regarding Zeke K.'s question:

> Last night I was eating dinner with my sister. She owns a boat on Lake
> Hartwell in Georgia, which was artificially created for both recreation and
> electrical energy production. The problem is that, due to drought, the lake
> is getting almost no inflow, but electrical demand remains high, so the
> level of the lake is falling. It is down 11 ft. from its usual height.
>
> Several groups have proposed pumping water from the lake that is formed
> below the dam back up into Lake Hartwell. Why bother doing this? As far as I
> can tell, this creates a net loss in energy.

This is certain.

> Might it have something to do
> with differing demands for electricity depending on the time of day?
>
> Marc "Zeke" Kossover

It very probably has nothing to do with "differing demands for
electricity depending on the time of day".  The rational way to
minimize the drainage of the lake in the face of fluctuating load
conditions is to simply restrict the flow over the turbines and
cut off all together those turbines that are unneeded to produce the
current local electrical power demand when it is slack.

My suspicion is that the clamor from the groups that are proposing
pumping the water back into the reservoir do not represent the
electrical utility that is operating the generation facilities at
the dam.  I suspect that they represent *other* interests connected
to the lake, e.g. boating, water skiing, fishing, resort interests,
etc. and maybe the property owners whose lakefront property has
become a useless unsightly mess from the receding shoreline.

My second guess about this is that probably the total amount of
electrical power produced by the dam is normally a small fraction of
the regional demand for electrical power, and that the dam only
contributes an marginal supplement to the overall energy budget.
This would give the recreational interests more local political
clout over the interests of the electrical utility.  If the dam
became a net sink of power instead of a net producer of electrical
power it would not make a super huge difference in the overall
scheme of things.  Other power plants from other sources (e.g. maybe
TVA-generated nuclear power) would, presumably, just take up the
slack (albeit possibly at a premium price--witness last year's
electricity fiasco in California).

David Bowman