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Storing wind-generated energy as gravitational potential energy? - Page 28

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Posted by harry on December 9, 2008, 7:58 pm
 

Denmark's windmills.
The UK gov. is bent on building lots of windmills at sea. However the
Danes have a major advantage over us, that is they can export surplus
power to Germany,  an option not open to us. We would have to shut
down.
There is a small DC link to France dating from the 1960s.  The idea
was electricity went both ways due to our differing peak demand
times.  These days, it's all one way. From the French to us.

Posted by The Natural Philosopher on December 9, 2008, 12:45 pm
 
BigWallop wrote:

The correct term is load average. What you actually get out i a year as
compared with what you would get out if te plant were operating at its
very best all year.

Dynamo Dve has cunningly presented data which confuses that with yet
another thing, what you NEEDED to produce all year, not what you COULD
have produced all year.

So

What John calls the 'plate' figure is what power the set CAN produce.

Lets say its a gigawatt.

For a modern nuclear power station it CAN produce 90% of that on average
over the year. The other 10% typically being fule reloading and down for
maintenance.

A windmill can produce 30% of that, As most of the time the wind is too
strong, or not strong enough.

or you can look at what power was actually drawn off the sets.

With nuclear, being as how they are very cheap to run,and te fuel cost
is minimal,thee is a tendency to run them flat out as much as possible
so they actually DO generate that 90% and sell it.

With wind, when they are all spinning like mad, chances are that they
are producing more than you want, and so you cant buy it all off them.

When they are all sitting doing nothing, they aren't making any anyway.
you have to buy power from expesnive fuel hungry gas turbines kept
permanently on warm standby.

But thats OK, because te wind companies are guaranteed a price for their
electricity that is way above what a nuclear set can command, and the
wind companies are not expected to pay for the fuel that keeps the gas
turbines on hot standby. And actually that burn more fossil fuel than if
there were no windmills at all.




That may be the conversion efficiency for what wind they have, though
its hard to see how its calculated.

What we are talking about is the average amount generated as a ratio of
the peak possible.

A very different thing.




Posted by Neon John on December 10, 2008, 8:26 am
 


Yep.  The cover article for "Power Engineering & Technology" magazine (a
biased trade rag, of course) a couple of months ago reported on an industry
analysis of what it will take to integrate even 30% wind power.  This is in
the US, of course.  The problem is exactly what you cite - what to do when the
wind quits blowing or the turbines break.  The US industry currently uses gas
turbines and pumped storage but it looking hard at molten electrolyte
sodium-sulfur batteries.  Utility-grade batteries are already in pilot testing
(beta test to you software nerds :-)

As you might imagine, utility sized NaS batteries are extremely expensive and
are of unknown reliability.

Us rationalists were proven correct a few months ago in another event reported
in the same magazine.  At one of Texas' largest wind farms, one day the wind
just.... quit.... blowing....  I forget how many MW capacity was lost but
according to the article, a wide-area black-out of the New York/Northeast
style was very narrowly avoided by some rather heroic actions by operators at
the grid control center.

Thing is, the loss of wind (or as I'm beginning to understand in your case,
too much wind) is something that is impossible to predict so hot standby
backup must be available on literally seconds' notice.

BTW, here, the term "hot standby" as regards turbines and similar non-coal
plants means that the unit is spinning and synchronized with the grid but
either not producing any power or perhaps generating some leading MVARs to
address grid PF.  "Warm standby" means that everything is set so that one can
hit the "start" button and practically instantly accept load but that the set
is not actually turning.  

The emergency generators at a nuclear power plant are maintained in warm
standby, for instance.  That is, the oil and water are heated to normal
operating temperature, the air starters are charged with compressed air and
all that is required is a contact closure in the "start" circuit to commence
generating.  The generators at Sequoyah are required by Tech Spec to go from
warm standby to full load in 12 seconds.  They actually do it in about half
that time.  

The air starters spin the engines up to operating speed, the compression
releases close, the injectors start firing and the engine is running.

Meanwhile us nukes keep on splitting those poor innocent uranium atoms, day in
and day out with boring reliability.  This takes about 3 seconds.  It takes
another second for the governor to stabilize the speed and perhaps another
second for the auto-sync "relay" (actually a control box) to sync the
generator to the grid and close the breaker.  During a blackout, of course,
the first generator would simply start.  The others would start and sync and
then the main load breakers would close.

At Three Mile Island Unit 1 (the one that didn't melt) I personally tested
their generators for response time.  They were even a bit faster.  Vital Bus
load is applied in stages to let the inrush current of one batch of motors
decay before applying the next.  

The control system watches the bus current and timed the load application just
as generator full load was about to be lost so as to keep the fuel injector
racks fully open during the whole startup sequence.  That way there is no
issue of what kind of response time constant the governor has.

The system before the accident was timer-based but we upgraded the control
system to event-based and then I tested it to make sure it worked properly. It
did and by a (typical for a nuke plant) huge margin.

"Hot standby" in a steam plant means that the heat source is operating (fire
in the boiler or reaction going in the nuke core), the steam is going to the
condenser and the turbine may or may not be spinning.  Hot standby is
typically maintained after a trip caused by an electrical situation while the
staff evaluate whether the plant can be brought back up or must be shut down
for maintenance.  It is also a stage in the startup sequence prior to having
load dispatched to the plant.  Hot standby gives plenty of time to "read the
gauges" and warm everything up at a slow enough rate not to cause damage.

John



--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com  <-- best little blog on the net!
Tellico Plains, Occupied TN
Democracy is three wolves and one sheep voting on what to have for supper.


Posted by David Hansen on December 8, 2008, 2:08 pm
 On Mon, 08 Dec 2008 01:52:44 -0500 someone who may be Neon John


On that point I agree with you.




--
  David Hansen, Edinburgh
 I will *always* explain revoked encryption keys, unless RIP prevents me
 http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Posted by Andy Champ on December 8, 2008, 9:23 pm
 Neon John wrote:

Thank you <blushes>

Oddly enough I don't care about the efficiency of conversion.  We have
lots of wind, and waste just as much on tress, houses and mountains.  I
do care about the *cost* of conversion though.

<snip>

 > From your description, Andy, it sounds like the UK thing is more a
 > publicity stunt than a serious attempt to generate power.

They're serious. That's a lot of dosh.  err moolah in US?  It's one of
the best places too, shallow water and near major power consumers.

Andy

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