Re: renewable energy

["John S. Denker" <jsd@MONMOUTH.COM>]

Leigh Palmer wrote:
> John Denker makes the common error of considering hydroelectric
> power to be a renewable resource. It is renewable only in principal.
> To obtain hydroelectric power economically one must build dams at
> special locations on rivers. Once these locations are gone no more
> hydroelectric power can be generated. Pondage behind dams silts up
> at a rate which typically has a horizon in time that is nearer than
> that for coal! Once all the good dam sites have silted up...

The coal-exhaustion timescale is not very long.  World
annual energy budget 400 quads and increasing;  21 million
BTUs per ton of coal;  world reserves one trillion tons of
coal.  Do the math.

  http://www.eia.doe.gov/kids/infocardnew.html

The oil-exhaustion timescale and the uranium-exhaustion
timescale are even shorter (assuming non-breeders).

In principle, nothing (dams included) lasts forever.  But
a dam doesn't need to last forever to significantly outlast
coal/oil/uranium.

A badly-designed dam may lose _flood-control_ capacity
due to siltation.  This may cause electricity-generation
capacity to become seasonal.  However the presence of silt
in the water does not, per se, change the energy budget of
the dam.  Density is the same (if not larger :-), height is
the same, flow is the same ....

A well-designed dam in a favorable site will come into
"equilibrium" with the silt load over timescales long
compared to the coal-exhaustion timescale.

If you want to get really picky, I suppose you could argue
that over geologic time, erosion will make the entire
landscape horizontal, but that's pretty long compared to
the coal-exhaustion timescale.

You might think hydropower is important because it is
virtually 100% of the present-day "alternative" energy
production.  But that's the wrong way to think about it.
Hydropower is a minor part of the energy budget (7% of US
electric power i.e. <2% of US total power).  There's not
much hope it could be expanded to become "the" solution to
"the" energy problem.  So it's hardly worth worrying about
whether hydro is "renewable" or not.