To: WSFAlist at keithlynch.net
Date: Tue, 20 Aug 2002 22:15:08 -0400
Subject: [WSFA] Re: power plant visible from 50 miles
From: ronkean at juno.com
Reply-To: WSFA members <WSFAlist at keithlynch.net>

On Tue, 20 Aug 2002 05:27:33 -0700 (PDT) Rich Lynch <rw_lynch at yahoo.com>
writes:
> Have to wonder who did the economic analysis of this
> project.  760 gigawatt-hours per year is 760 billion
> watt-hours per year of electricity.  If you assume
> 100% onstream factor, that's 8,760 hours per year.  Do
> the division, and that works out to only about 87
> megawatts -- not even the equivalent of a small gas
> turbine power plant.

I made the same calculation before forwarding the message, and got the
same answer: 87 MW.  However, it should be noted that a plant which
produces 760 GWH/Y might have a capacity much greater than 87 MW.  Most
power plants which are not 'base load' plants operate at less than 50% of
capacity averaged over a year, so I was thinking that this plant might
have a peak output in the neighborhood of 200 MW, not that that would
necessarily make much difference in the economic analysis based on energy
value.   The 200 MW figure is not inconsistent with the 'energy for up to
200,000 homes' mentioned in the article.  Perhaps the plant would crank
out far more than 87 MW at just the times when air conditioning is in
highest demand, making its output more valuable at times, than the
average price of energy over the year.

Consider that the 'greenhouse' is 7 km across, or 38 square km.  Each
square km will average roughly 1000 MW insolation power during most of a
sunny day (and sunny days are the norm, there, I think), so the gross
thermal power entering the greenhouse over most of the day would be 38
GW, very roughly.  Assuming the plant actually would have an electrical
output capacity of some 200 MW, the overall thermal efficiency need only
be about 0.5%.  At 100 MW, 0.25%.  The low efficiently is presumably
mostly due to the small temperature difference and the use of low
pressure turbines.  Of course the plant would normally continue to run
all night at reduced power from the heat stored in the top layer of earth
under the greenhouse, and would also run at reduced power on occasional
cloudy days.

...

> If we assume all of that income is used to pay back
> investors at the minimum 15% ROI rate, that means the
> capital costs of the project can be no greater than
> US$60 million (or else you drop below the 15%
> threshold).
>
> No way that monstrosity gets built for $60 million.
> It probably can't be done for ten times that.

The tower would be 130 meters wide, but mostly it only needs to be a
frame and a skin, and it could be guyed, rather than free-standing.  It's
less than 8 times tall as wide - fairly broad-based.  The base could even
be flared, if desirable, while maintaining an inner skin 130 meters
across, within the flared structural frame.  It could also be internally
braced with cables, if wanted, since cables won't interfere with air
flow.  In Poland in the 1970s they built a 2000 foot tall guyed tower for
TV broadcasting.  It was the tallest tower in the world, not equaled
since, but it fell down after a few years, allegedly due to poor
maintenance, and not necessarily because the idea was inherently flawed.

If the tower cost $1,000 per meter of height, that would be $1 million
for the tower.  If the tower cost $10,000 per meter, it would $10 million
for the tower.

Then we have the greenhouse.  Most of it could just be
translucent/transparent skin on stilts, internally braced with cables.
Perhaps plastic sheet bonded to a graduated net of fiberglass twine/rope
for strength.  At 38 million square meters, even as cheap as $1 per
square meter, it would cost $38 million, and at $10 per sq. meter, $380
million, so the greenhouse might be the single costliest item.  Turbines,
generators, transformers, and transmission lines would also be required.

Such flimsy structures (the tower and greenhouse) would not hold up
against a tornado, but the thinking might be that the chances of a
tornado hitting the structure during its intended lifetime are negligible
(unless, maybe, it spawns tornados).

> So why
> is it being done at all?

The cost mentioned in the article was UKP308 million ($450 million), so
maybe it is being subsidized on the grounds of air pollution control,
'prestige' (the world's tallest tower), a learning curve cost for new
technology, etc.

Ron Kean

> http://www.newscientist.com/news/news.jsp?id=ns99992688
> >
> > Kilometre-tall power tower approved
> >
> > 14:35 19 August 02
> >
> > NewScientist.com news service
> >
> > Plans for a one-kilometre tall "Solar Tower" that
> > would provide clean
> > energy for up to 200,000 homes have been approved by
> > the Australian
> > government.
> >
> > But some environmental campaigners are questioning
> > the practical benefits
> > of the scheme.
> >
> > The 130 metre-wide tower would produce electricity
> > using currents of air
> > heated by the Sun's rays.  The tower itself would be
> > surrounded by a vast
> > greenhouse, seven kilometers across.  Hot air inside
> > the greenhouse would
> > be effectively sucked up the tower through turbines
> > at its base.
> >
> > Heat-storing material inside the greenhouse would
> > continue to heat air
> > during the night.
> >
> > The massive structure would be more than twice as
> > tall as the Petronas
> > Towers in Kuala Lumpar, and visible from 80
> > kilometres away.
> >
> > Australian company EnviroMission plans to build it
> > in the desert on the
> > border between New South Wales and Victoria.
> > Australia's federal
> > industry minister put the £308m project into a
> > fast-track planning
> > process on Thursday.
> >
> > Fossil fuels EnviroMission says the building would
> > generate 760
> > gigawatt-hours of energy per year.
> >
> > Roger Higman, senior climate campaigner for Friends
> > of the Earth, is
> > concerned that construction costs could outweigh the
> > potential benefits.
> >
> > "If they're planning to build a truly enormous tower
> > they could use a lot
> > of fossil fuels," Higman told New Scientist.  "It's
> > not as if we are
> > short of ways to generate electricity without using
> > fossil fuels."
> >
> > Higman adds that a conventional wind farm could
> > produce a comparable
> > amount of power without requiring so much
> > construction work.
> >
> > A smaller 200 metre tall prototype Solar Tower was
> > built by a Spanish and
> > German team in Spain in 1982.  If the New South
> > Wales state authority
> > gives approval for the new tower, construction work
> > could begin in 2003
> > and the structure could be completed by 2005.
> >
> > Will Knight .
> >
>
> =====
> Rich Lynch
> ==========
> MIMOSA web site: http://jophan.org/mimosa/
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>
> __________________________________________________
>

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