[pf] Green power generation

** This goes to Positive Futures, an illustration of how I use my
knowledge; /anyone/ with the equivalent of Grade 11 Physics could do the
same.  D.

**  Earlier I had said:
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At 11:34 19/7/2000 +1200, Trevor Reeves wrote:
>I'm not surprised hydro wasn't included as "green" generation. Storage lakes
> ...

**  I'll comment after lunch; this is just to note that storage lakes are
not an inherent part of hydro-electric power generation; they have been,
but when you have a grid, they don't have to be big lakes.

David.

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At 11:34 19/7/2000 +1200, Trevor Reeves wrote:
>Hello David,
>I'm not surprised hydro wasn't included as "green" generation. Storage
lakes actually produce more greenhouse gasses than the land they replace.
The other "ungreen" facet of hydro is the amount of productive agricultural
land the storage lakes replace. Not to mention living environments of
course, as in China's 3-gorges project, displacing millions of people on to
unproductive, desert land. In fact, hydro is the most ungreen of all
ungreen generation methods - including nuclear, which is relatively clean
compared to most. Hydro not only destroys the land under the storage lakes
but much of the riparian strips around it, with weeds and erosion, use of
presticides indiscrimately to "control" it etc. Landcorp do it at
Mahinerangi - spraying from helicopters, killing fish into the bargain. My
preferences are wind and solar - solar being able to produce as much
electricity as hydro, which uses ten times the land mass than solar,
destroying the land in the process.
>
>See our site on the Mahinerangi/Waipori generating scheme:
www.converge.org.nz/sms
>
>Trevor Reeves.
>

**  I'm sorry to have to argue with you, a person who has obviously "stood
up and been counted" against man's excessive /use/ of the earth.

**  However, I can't let such bald statements as your:

"In fact, hydro is the most ungreen of all ungreen generation methods" 

go by unchallenged. I've left your whole letter in, so other readers can
see that your main point is, I believe, that large hydro dams are as bad a
use of land as a city is.

**  So I ask that you qualify any such bald statements by the addition of
"dams" to "hydro", or the use of "large", etc.

**  Several points:

**  What is wanted is energy, supplied to the (local town or) grid when
needed. The original is the potential energy of the water, available after
it lands on the ground as rain in the high country. (I may come to tidal
energy later; it also produces hydroelectric energy.) The water coming
downhill in streams, creeks and rivers loses energy through turbulence etc.
until all that stored energy has changed so it slightly warms the water by
the time it reaches the sea. This happens continuously, i.e. it is a
renewable, green energy source.

**  The question is /how/ to harness that, convert it to electricity (or
motion in the old water-mills), in a way that doesn't have much effect on
nature. Not _no_ effect, just a sufficiently small effect that this manner
of getting energy is sustainable, which I take as (1) a method which will
certainly still be in use in hundreds of years and more, and (2) the
overall impact of the homo sapiens species on other species is not greater
than the typical impact of one species on another. ("typical" excludes the
current human impact and that of eucalyptus and similar exclusive species.)

**  For over a century methods have been known for extracting the energy
from falling and flowing water; these methods vary greatly in their impact.
   The physics of it is in the mass-per-second times the pressure, this
latter coming from the height, the former from the flow rate through the
turbine. The two extremes can be seen in (a) the high-pressure low-flow
micro-hydro I'll be considering for the winter stream up the hill behind
our house in the Kauaeranga, to supplement the PV system in the low sun and
short days winter period; and (b) a huge mass-per-second run-of-the-river
hydro-electric installation not visible or hardly-visible in a /big/ river
like the Yangtse, the Mississippi or the Amazon, and what they should have
used in the Nile, IMO, instead of the Aswan High Dam. I've also considered
it for the bottom of our property which runs along the Kauaeranga River
which has rapids as it goes past us.

**  Early dams, e.g. at Karapiro on the Waikato River and most others in
New Zealand, were put in when the engineer was king, and when environmental
impact hardly got a look-in. And the worst by a long way is, as you point
out, the 3 Gorges Scheme in the middle reaches of the Yangtse (before it
gets out of the hills). It's perhaps understandable that the whole
hydro-electric enterprise gets tarred with the same brush, but /I/ think
that's being far too simplistic. Comparable to saying (IMO) that since
almost all violent crime is committed by men, that men are bad and should
be suppressed. That's not a joke, by the way - for some years /I/ felt that
way about my gender.

**  It has been for /convenience/ not necessity that these "big" dams have
been built; the bare minimum in the way of a dam is to be able to hold back
water during the day sufficient to store the energy produced by the
photo-voltaic (PV) generating capacity in the system, then releasing it at
night. That isn't much, almost certainly less than the amount by which the
river level itself changes during the year.

**  I remember walking through the woods of northern Ontario (I lived there
during the 60s and 70s) and quite unexpectedly coming across a nearly 100
year old concrete dam in a creek, less than 2m high, with a box at the foot
containing the turbine and generator, and with a fish-jump built into the
overflow flume. I say unexpectedly since the trees, bushes and other
wildlife had completely adapted to its presence; I'm sure it had a pretty
small effect a decade or so after it was built.

**  I mentioned the engineering and operational convenience of a single
fairly high dam. It could well be cheaper, though I remain to be convinced
of that. I know of /no/ inherent reason why a single large impoundment
(dam) couldn't be replaced by a string of weirs (at the most) each with its
generating set.

**  So once again, it's the current over-emphasis on "the bottom line":
minimising costs and maximising profits, that is the cause of the problem,
not hydro-electric generation itself.

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sent to the Pos Fut list by David.

(David MacClement) davd@ihug.co.nz 
http://www.emucities.com.au/member/davd/index.html#top
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