From: robg@citr.uq.oz.au (Rob Geraghty)
Subject: Re: SEQEB and ads
Keywords: off-peak, hot water, clean
Organization: Prentice Centre, University of Queensland
Distribution: aus
Date: Wed, 4 Nov 1992 04:46:36 GMT

dan@cs.uq.oz.au (Dan Johnston (D.B.)) writes:

>In <robg.720760307@citr.uq.oz.au> robg@citr.uq.oz.au (Rob Geraghty) writes:

>I think there are a couple of inaccuracies here. I believe that some "spinning
>reserve" is maintained constantly to handle emergencies (perhaps 1 machine)
>but not all machines.

I think you'll find that once assembled, the turbines actually have to
be kept spinning by some means.  It may be that they use electric motors
to do this when the generator is offline.  I'm not sure.

>Before Tennyson power station shut down, we used to see it produce
>particularly black smoke during startup in the winter afternoons as they
>powered up for the peak load. (The colour improved after a few minutes.)

I certainly wasn't suggesting that *all* generators were held at peak
capacity.  As someone else pointed out to me, there is probably a great
deal more energy lost in the actual transmission of the power from the
generator to the consumer.  Brisbane actually gets a lot of its power
from Gladstone - the losses over that distance are quite significant
though I cannot quantify them.  I would expect the Snowy Mountains
Scheme suffers a similar fate.

>I believe that the inefficiency in use of electricity is primarily due to the
>inefficiency of the generation process (heating steam turning turbines and
>then cooling it again). My thermodynamics is very rusty (>20 years) but I
>believe that this process has an efficiency of less than 50% and is related
>to the maximum temperature of the steam (limited by properties of the metals
>used in turbines etc) and the temperature of the cooling water.

I think that coal-fired steam turbines have an efficiency of around 20%.
Remember also that you have the added inefficiency of generating heat at
the consumer's water heater as well!

>Splityard Creek Dam is used in this way. Water is pumped up from Wivenhoe Dam
>during off peak times and is used to generate electricity at peak periods.
>Of course, there must be some loss in this process, but I believe it is
>relatively efficient. The main advantage is the saving in capital cost of
>equipment to handle peak loads.

You're right.  I would be interested to know what proportion of the peak
Splityard Creek is actually capable of handling.  It appears to be a
*very* small hydro-electric plant.

>>Cleaner than "demand" electrical heating yes.  Cleaner than gas?
>>Debatable.  Cleaner than solar?  Impossible!
>Don't forget the amount of energy that goes into producing your solar
>collector. I believe that I have seen it stated that more energy goes into
>producing the aluminium for a solar hot water system than it is likely to
>save in its lifetime.  I suspect that producing solar cells may also be
>energy expensive relative to their production of electricity.
>Can anyone make an authorative comment on this?

Seconded!  I would also be interested to see an unbiased analysis of the
energy cost of different water heating systems.  Also the cost to the
environment!
Is the argument about the aluminium needed to make a solar collector a
spurious one?  What about the energy required to produce the copper and
insulation used in a conventional gas or electric water heater?  I guess
you *still* need a reservoir for a solar hot water system...
I have also seen the argument used against solar cells that the energy
required to produce them is greater than the energy they will generate.
Of course, ideally we should use renewable energy sources to generate
the power to make the cells.  But with so little momentum in the
development of alternative energy sources, I guess we'll have to wait
until the coal runs out... *sigh*

Rob

--
------------------------------------------------------------------------
Rob Geraghty               | 3 things are important to me 
robg@durian.citr.oz.au     | The gift of love, the joy of life
CITR                       | And the making of music in all its forms