From: dan@cs.uq.oz.au (Dan Johnston (D.B.))
Newsgroups: aus.conserve
Subject: Re: SEQEB and ads
Keywords: off-peak, hot water, clean
Date: 3 Nov 92 23:58:46 GMT
Reply-To: dan@cs.uq.oz.au
Distribution: aus

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

>grantpa@tplrd.tpl.oz.au (the old man in black) writes:

>>During the day, heavy demands are placed upon the electricty grid, particularly
>>6-9am and 5-8pm.An electrical demand water heater will use power when required.

>I am aware of base loads and peak costs.  Note that I was comparing
>off-peak electrical to gas or solar water heating.

>It is actually the gaussian nature of electricity demand that makes it
>*inefficient*.  Enough generator capacity has to be online to handle the
>peak.  Engineers correct me if I'm wrong, but in Queensland most power
>generation is by coal-fired genrators.  These generators must spin
>constantly - so they *always* require some energy input.  This is why
>off-peak electricity is so cheap - they want to use the spare capacity
>that must be kept online.
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.
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 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.

>>Overnight, there is spare generation capacity (this is in part used to pump
>>water up hill in the snowy mountains scheme. Snowy is used as a fast acting
>>reservoir of energy during the tops of the days peak periods). This can be
>>also used for hot water generation.

>I believe that the snowy scheme is used as a load leveller in southern
>australia.  However I don't think it has any effect up here.

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.

I believe that a process that goes directly coal -> heat will be much more
efficient than any process that goes via electricity irrespective of the
economies of scale, etc.
Likewise, use of gas will be much more energy efficient than use of
electricity. (and will produce less CO2)

>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?

    dan.
dan@cs.uq.oz.au  (Dan Johnston)