Wikipedia intermittent power source

[Dave A]

Attached article from Wikipedia has been copied to the discussion forums...

http://en.wikipedia.org/wiki/Intermittent_power_source

Some people have claimed that Wikipedia is unreliable since anyone can edit it. However in my experience this is simply not true. There is a whole army of pedantic editors who will remove any statement that is not reliably sourced, or is perceived as bias. It seems to me that this article ( well the introductory section anyway, ) is a pretty fair summary.

any comments?

Note several of our members are referenced.

Would be good to continue this discussion on the forum.

http://www.claverton-energy.com/foru...ment-transport

Thanks

Dave Andrews


Intermittent power source - From Wikipedia, the free encyclopedia




An intermittent power source is a source of electric power generation that may be uncontrollablyvariable or more intermittent than conventional power sources, and therefore non-dispatchable, and is usually used to refer to sources of renewable energy such as wind and solar generated electricity.
At present, the penetration of intermittent renewables in most power grids is low, but wind for example has reached about 17.5% in Denmark in a normal wind year [1] (where plans are underway to increase this to in excess of 50% by 2025 [2][3]) and 7% [4]in Germany. In small amounts, integration of intermittent power sources has little effect on grid operations, but the more variable and intermittent nature of power generation from these renewable sources compared to conventional sources has raised concerns, by no means universal, about the ability of electricity grids to absorb large amounts of this intermittent power to replace the output of conventional power sources, and the economic implications. However technological solutions to deal with intermittency already exist see Control of the National Grid (UK), and studies by academics and grid operators indicate that the cost of compensating for intermittency is expected to be low even at levels of penetration substantially higher than those prevailing today. For example, in evidence to the House of Lords Economic Affairs Select Committee, the UK System Operator, National Grid have quoted estimates of balancing costs for 40% wind and these lie in the range £500-1000M per annum. "These balancing costs represent an additional £6 to £12 per annum on average consumer electricity bill of around £390 [5]
Given that power demand on existing grids varies substantially and on different time scales (seasonally, daily, for weather-related reasons and the like), matching power demand to supply is not a problem specific to intermittent power sources. All generating sources have some element of randomness (including unforeseen breakdowns) and differing capabilities to vary output or shed loads in response to either sudden and large changes demand or sudden and large changes in available power generation. Hence power grids are already designed to have some capacity in excess of projected peak demand, including for sudden loss of conventional power plants.
As a report from the IEA puts it "In the case of wind power, operational reserve is the additional generating reserve needed to ensure that differences between forecast and actual volumes of generation and demand can be met. Again, it has to be noted that already significant amounts of this reserve are operating on the grid due to the general safety and quality demands of the grid. Wind imposes additional demands only inasmuch as it increases variability and unpredictability. However, these factors are nothing completely new to system operators. By adding another variable, wind power changes the degree of uncertainty, but not the kind - a fact that several authors referred to recently (DeMeo et al. (2003))." [6]
In the context of global warming, some argue that the main benefit of renewable energy sources is reducing overall emissions by displacing fossil fuel generation. Others argue that most power generation, particularly electricity, can be generated from renewable (intermittent) sources using existing technology.
A series of detailed modelling studies by Dr. Gregor Czisch, which looked at the European wide adoption of renewable energy and interlinking power grids using HVDC cables, indicates that the entire European power usage could come from renewables, with 70% total energy from wind at the same sort of costs or lower than at present. Intermittency can clearly be dealt with, according to this model by a combination of geographic dispersion to de link weather system effects, and the ability of HVDC to shift power from windy areas to non-windy areas.[7][8][9]

Claverton Energy Group
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Dave.Andrews@energyresearchgroup.eu

[Richard Lawson]

The intermittency argument is not at all the knock out blow that the opposition imagines it to be.
First, wind is not unpredictable. That is what the Met Office is for.
Second, a large PV source will help to balance things out, since the sun usually shines on high pressure, non-windy days.
Third, the European HVDC grid will even out the regional variability.
Fourth, grid balancing can be enhanced by means of energy storage. As well as the pumped storage systems, electrolysers brought on stream when there is overproduction in the grid can generate hydrogen and oxygen from power that would otherwise be wasted.
http://www.electrolysers.com/
The above link claims high efficiency.
A bidirectional fuel cell would be ideal, since it could use power at times of overproduction, and generate power at times of high demand.
A large fleet of plug in hybrids would do the same job.

[admin]

-----Original Message-----
From: Dave Andrews [
Sent: 19 October 2008 18:14

Cc:
Subject: RE: GT +CCGT Output Ramp rates

David Bowie - very interesting - is the unit at White City still operating - maybe that is the Taylor's lane you mentioned.

Have posted this to the forum

Best

Dave Andrews

Subject: RE: GT +CCGT Output Ramp rates

Chris,

Returning to the availability of OCGT plant in the UK, during the grid
disturbance of 27-05-08 National Grid secured some 800MW of output from open
cycle gas turbine units within a couple of minutes of the initial
disturbance. In the main these were distillate oil-fired auxiliary GT plants
attached to the main thermal stations. However, larger plants at Taylor's
Lane and Cowes also contributed. A further 282MW of GT generation still
remained available as reserve.
The manner of the simultaneous despatching of all of these units -- some 31
machines in total -- would appear to indicate that the grid control software
presents the engineer with the option of a "rapid mass start" of all of
these generators. The response from GT plant was in fact greater than that
from pumped storage generators that morning; 810MW GT vs 584MW of additional
pumped storage output having been secured.
Also of interest is the circa 50MW OCGT plant at Fort Dunlop; I know little
about this station, but it appears to be a new-build peak lopping GT plant.

Regards,
David Bowie

-----Original Message-----
From: Chris Hodrien [\
Sent: 17 October 2008 00:20
To: andrews Claverton; andrews Claverton; George Wallis; st
Subject: Re: GT +CCGT Output Ramp rates

Fred, I quite agree, designing a CCGT with a duct burner (NB prob' very
difficult/impossible to retrofit to existing CCGT's) would give a great
degree of flexibility especially when running on spinning reserve or
part-load for WT back-up.
I remember studying the "once-through" HRSG boiler option that you describe
back in 1993-99, smart option re. 2-shifting, I wrote a report recommending
it to BG power Gen dept. The specialist supplier that I dealt with was IST
(in USA). Pity more UK CCGT's weren't built with it (-were ANY?). It seems
to have been mainly restricted to the smaller plants, and mainly in
US/Canada.

The vast majority of CCGT's in UK and worldwide still have separate
alternators for the GT and ST's, the "single-shaft" variant only has a
15-20% market share despite being more compact and cheaper, presumably
because of operational inflexibility (....despite having clutches). Lots of
past "chapter and verse" on this choice in past GT World issues or GT/power
conf papers.
Regards all, Chris.

>

[admin]

----- Original Message -----
\
\
Sent: Thursday, October 16, 2008 11:09 PM
Subject: Re: FW: (EXISTING) Wind Output Ramp rates


>
> Dear George, Chris and David,
>
> Because changes in wind output are fairly sluggish,
> even when at their most rapid, a two hour time to full
> power from a CCGT would be fine.In practice CCGTs can
> be running at full output after an hour.There is also
> a form of HRSG called a once through system which is
> designed for very quick start ups.
>
> The main virtue in eliminating the steam system,is
> that it gets rid of possible maintenance
> problems.These would be caused by possible downtime
> corrosion on the water and air sides of the HRSG
> exchangers.The other problem is that of thermal
> fatigue. These issues were discussed by me in
> Renewable Electricity and the Grid
>
> The "Once Through HRSG" avoids these problems since
> the exchanger is constructed of a stainless alloy
> called Incoloy 825. In this cold water is pumped into
> the inlet and it changes to superheated steam.On
> shutdown the exchanger is allowed to boil itself dry.
>
> But various tricks can be employed, to at least
> minimise corrosion and thermal fatigue on conventional
> HRSGs.
>
> One commercial problem with conventional open cycle
> machines is that they are aeroderived and expensive,
> even though they are quite efficient.Another drawback
> is that the power output is quite low. 60MW is what
> can be obtained from Trent.This does not compare with
> about 250 MW for a Frame 9F.This excludes the steam
> cycle which will add about another 100 MW.
>
> One other advantage of CCGTs is that, in principle,
> CCGTs can use duct burning before the HRSG to increase
> steam output.Such machines would be great for meeting
> peak loads.
>
> I think your point about CCGTs running open cycle for
> a couple of years, before bringing on the steam
> system, may refer to older designs were there was a
> separate alternator for the gas turbine and steam
> turbine. But I am not sure about this.
>
>
> Best regards
>
> Fred

[admin]

>
>
>
>> Fred, thanks
>>
>> So far as I know existing CCGT also uses one shaft
>> for both turbines. The
>> point I was questioning was whether CCGT could be
>> run OC after completion,
>> since the plants run OC during construction to
>> provide better economics in
>> the construction phase.
>>
>> A number of posts have suggested that moving towards
>> higher wind/other
>> renewable penetration in the future would require
>> the construction of many
>> rapid response OC plants. As Chris mentioned 'if the
>> economics were made
>> right' one could have the best of both worlds with
>> only EXISTING plant.
>> Please see below - I think Chris may have been
>> responding as much to this as
>> the first email
>>
>> '(From Dave A) BUT I AM NOT AWARE IF YOU CAN RUN
>> CCGT OC - MAYBE YOU CAN..
>>
>> As I mentioned previously someone please tell me if
>> I'm talking rubbish.
>> Bear with me here. A CCGT plant is a careful
>> combination of a gas turbine at
>> one end of the generator and a steam turbine at the
>> other; normally both
>> turbines run and a plant will generate as the grid
>> market dictates. The gas
>> turbine can be run up from cold in minutes, with a
>> period of a couple of
>> hours elapsing before the steam turbine joins it.
>> When a CCGT plant is being
>> built the fuel supply, gas turbine, stator etc. and
>> grid connection are
>> normally installed first, and the plant is run as OC
>> for a year or two until
>> the steam plant is ready - better economics since
>> the plant is generating at
>> least some power much faster in the construction
>> phase. (It's good plant,
>> pity we don't have more gas.) If we are talking
>> about large amounts of
>> balancing to within a matter of minutes (cold) or
>> seconds (idling), I don't
>> know (correct me) of any reason why a CCGT station
>> can't run up only its gas
>> turbine, using the resultant exhaust merely to keep
>> its steam plant in a
>> state of advanced readiness. Compared to dedicated
>> OC plant it would be
>> slightly less efficient and more expensive, though
>> using (some) CCGT plant
>> in this way could be more flexible, in that the
>> steam plant could also be
>> run up in the event of major outages, and there are
>> a lot of CCGT stations
>> out there. Even if there aren't any technical
>> difficulties I would think the
>> economics would scupper it, but maybe something to
>> consider?'
>>
>>
>> Subject: RE: (EXISTING) Wind Output Ramp rates
>>
>> Dear George
>>
>> Commonsense and observation suggests that the ramp
>> rates can be estimated. It is highly unlikely that
>> the
>> wind output would drop from 60GW to zero in less
>> than
>> 24 hours.
>>
>> This gives a average ramp rate of 2.5 GW per hour.
>> If
>> we had 100 units of coal,gas and nuclear, each with
>> a
>> peak output of 600MW, the average ramp rate per unit
>> would be 25 MW per hour.There would be no problem.
>>
>> In practice, some fossil or nuclear units would
>> always
>> be running at about 75% of full load so as to take
>> care of the short term vagaries of the wind and also
>> of variations demand.The demand variations are much
>> more instantaneous of course.
>>
>> In practice we would probably have perhaps 10 CCGTs
>> which could provide 5GW very quickly, from then
>> onwards it would be up to the coal plants.Most of
>> these could be running at full output in 24 hours.
>>
>> Demand can also be controlled through voltage and
>> frequency giving about another 1 GW with which to
>> play.
>>
>> I don't think converting CCGTs to open cycle gas
>> turbines is necessary or realistic. In the CCGTs
>> that
>> will be built in the next 15 years, gas turbine and
>> steam turbine will share a single shaft driving one
>> alternator.
>>
>> Fred

[admin]

>>

>>
>>
>>
>>
>> > Fred and all
>> >
>> > 'However, there might be 10-20 times in the year
>> > (not just a week) when all
>> > of it would be needed, sometimes for just a few
>> > hours. But it will all be
>> > needed!'
>> >
>> > Do we know what ramp rates would be necessary? If
>> > not we urgently need to
>> > find out.
>> >
>> > 'But what about periods when there is an excess of
>> > wind? This spare energy
>> > could be used to produce hydrogen or be used to
>> heat
>> > water in district
>> > heating systems.'
>> >
>> > Much as I like district heating, large plant (and
>> > 2nd law) efficiency would
>> > seem to suggest we go for H2 (or CH4) CCGT?
>> >
>> > I'll again mention the big stinky elephant of LT
>> > thermal in the room...
>> >
>> > Regards, George
>> >
>> > -----Original Message-----
>> >
>> > Sent: 14 October 2008 18:01
>> > To: Chris Hodrien;
>> > 'George
>> > Wallis';
>> > 'Hugh Sharman (Clav Gp)'; 'Mark Barrett
>> (Claverton-
>> > UCL)'
>> > Cc: 'George Hay'
>> > Subject: Wind Output
>> >
>> >
>> > Dear Dave and Chris
>> >
>> > Please listen, both of you.
>> >
>> > The 180 GW is a possible 2050 target for wind,
>> which
>> > could conceivably be built over the next forty
>> > years.This implies an average build rate of about
>> > 4.5
>> > GW per annum, which should be achievable.
>> >
>> > But up to 2050 and well beyond there will be a
>> need
>> > for standby plant. This could be coal or even gas,
>> > much of which has yet to be built.So there will be
>> > no
>> > shortage of standby plant
>> >
>> > As we get nearer 2050, most of this standby plant
>> > would not be running most of the time.However,
>> there
>> > might be 10-20 times in the year (not just a week)
>>
>> > when all of it would be needed, sometimes for just
>> a
>> > few hours.But it will all be needed! My guess is
>> > that
>> > the annual load factor of the standby plant would
>> be
>> > in the 5-10% range.
>> >
>> > Turning now to the wind farms in 2050, on the
>> basis
>> > that the average load factor from wind is 23%,
>> this
>> > would give on average 41GW of power. This level
>>
> === message truncated ===

[gmailguy]

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