Talk:Intermittent energy source

Intermittent power sources - new page in need of editing

This page was established to shorten a significant and long portion of the Wind Energy article, and to allow for more in-depth discussion of this subject here. In need of editing. Contributions welcome. --Gregalton 09:42, 17 November 2006 (UTC)

Nota bene: There has been considerable discussion of intermittency in the talk pages for Wind Energy. For further background, you may wish to look there (until they are moved to this talk page).--Gregalton 12:43, 17 November 2006 (UTC)

Thanks for your efforts, Greg. I've pulled the discussion from the Wind Power talk page on this topic below. Skyemoor 13:52, 17 November 2006 (UTC)

I've just reorganised the long section on intermittency of wind. This section needs to be checked for references, NPOV, and other issues, but hopefully this regrouping of the issues will make it easier to edit further and make the arguments more coherent. There is some duplication that can be better seen now. Other "to-dos": it could really use more on variability of other power sources, especially renewables, i.e. solar and potentially water. At present, this is really a page about wind variability and comparisons would be useful.--Gregalton 21:59, 19 November 2006 (UTC)

Intermittency - an over stated problem?

[edit] Frequency Service and Reserve Service

this is a usefull link.... http://www.ukerc.ac.uk/content/view/258/852 looking at the actual intermittency / variability of wind in the UK,

Another useful contribution - looks at renewable power, largely wind over a vast area. – a European/Transeuropean Example –

Dipl.-Phys. G. Czisch, Prof. Dr.-Ing. J. Schmid

Institut für Solare Energieversorgungstechnik (ISET), Kassel, Germany

Phone/Fax: (+49) 561-7294-359/100, E-Mail: gczisch@iset.uni-kassel.de

http://www.google.co.uk/search?hl=en&q=windpower++europe+interconnected+grid+sahara&btnG=Search&meta=

The national grid in the UK already is a massive user of technology to cope with the existing intermittency introduced by power stations themselves, at an industrial scale - up to 2 GW of load can be lost instantaneously by frequency sensitive relays switching of steelworks etc, which is matched over a 20 minute cycle by up to 2 GW of quite small emergency diesel generators. (These are already owned and paid for, for use as emergency generators by eg hospitals, water companies etc)

For a complete description of this complex but robust system, in use for many years, see for example "Emergency Diesel Standby Generator’s Potential Contribution to Dealing With Renewable Energy Sources Intermittency And Variability" - a talk by David Andrews, Energy Manager at Wessex Water a large utility who, along with other similar companies, work closely with the UK National Grid to provide this service. This was given at the Open University Seminar " Coping with Variability - Integrating Renewables into the Electricity System - A one day conference on Tuesday January 24th at the Open University, Milton Keynes." 24th Jan 2006 .

http://eeru.open.ac.uk/conferences.htm

For Wiki article based on the above: http://en.wikipedia.org/wiki/How_the_UK_National_Grid_is_presently_controlled

Up to 5 GW of such diesel generation is also used in France for similar purposes, but the fact of the widespread existing use of these techniques seem to be relatively unknown even by the pro wind lobby.

There is no reason why this type of simple and proven scheme should not be increased in scope to cope with even the intermittency introduced by a close to 100% (in terms of annual energy delivered from wind power), which would in fact be less than the intermittency already inherent due to the unreliability of large power stations - for example in the UK Sizewell B can impose an instantaneous cut in generation of 1.2 GW, which is far more severe than the swings which could occur in a 100% UK wind scenario.

http://david-andrews-wind-energy.wikispaces.com/

I don't think the intermittency problem is about load, but about supply; what would happen if all power plants were replaced by wind, and the wind can't provide adequate power for hours or days at a time. — Omegatron 21:22, 7 November 2006 (UTC)

1...If all the power plants were augmented, ( not replaced) by sufficient turbines for 100% wind, then all that happens is that sufficient of the power stations, which have all been retained, are simply started up to provide the power for the 5% or so of the year when there is insufficient wind. Remember they have already been built, and paid for and the bulk of the cost of a power station, is the fuel - 96%. So keeping it idle, is in fact very cheap. The cost of keeping a UK power station idle can be worked out from the Spark Spread,

http://en.wikipedia.org/wiki/Spark_spread#Clean_spread

which is the published profit of a power station, and is about 0.75p/kWhEngineman 21:59, 8 November 2006 (UTC)

The point of mentioning load, is to show that routinely large grid systems shed load as a matter of course to cope with the existing inherent intermittency of the power stations, surprisingly, this fact is not apparently well known to wind power experts.Engineman 21:59, 8 November 2006 (UTC)

The intermittency problem is about load and supply, like supply and demand. Load can vary dramatically, and it is precisely the peak events (three-sigma and above) that cause problems,

I do not think this statement is true - a large drop in power supply is more stressful on a system at times of low load than the same drop at high load, simply because it will be a bigger proportion of the capacity. Peak load is not itself a problem provided you have built enough plant to deal with it.Engineman 21:59, 8 November 2006 (UTC)

Also load changes, although they can be a bit bigger, are much slower than the loss of a power station, so they are not the ruling issue. It’s the unreliability of the power stations which determines the size of sheddable load available and spinning reserve, not the variability of the load Engineman 21:59, 8 November 2006 (UTC)

In the context of wind, the intermittency problem is peak load coming at times of low supply from non-dispatchable sources, i.e. wind. So having "enough plant" is not enough - it also depends on what type of plant. Load shedding is also essential, but it is also not without cost. --Gregalton 08:20, 9 November 2006 (UTC) even if they occur quite rarely. While I agree with you that supply is also the issue, it is a red herring to discuss "what if all power plants were replaced by wind", since there are almost no systems with penetration above 10%.

No - I think you have got this wrong. If there is not enought wind at peak times, during a 100% wind scenario, you just start up the old power stations that have been kept fully manned and on standby. This is not expensive since the major cost of running a power station is the fuel cost. Engineman 22:30, 13 November 2006 (UTC)

Wind increases variability of supply (or of net load, if one prefers); the question is how much it may cost to compensate for this - presumably while holding system integrity constant.

Frequency Service is very cheap - £7k/MW per year, which amounts to say £7000/1000kw x 8760 x 60% = 0.133p/kWh in the UK at the present - look it up on the National Grid website.

Other supply sources or reduced volatility of demand (by peak demand management) are both potential means to compensate. As noted in the text, the scenario of "wind providing inadequate power" (presumably what is meant is significantly below projected norms) becomes less likely as spatial diversity between wind farms grows. --Gregalton 22:57, 7 November 2006 (UTC)

I beg to differ - it does not seem logical to say that a 100 % wind is a red herring simply because there is no existing penetration above 10%, when what is being seriously proposed is precisely that 100 % wind, (ie enough to generate over a year the same amount of power that the grid delivers to customer) is a practicable scenario.Engineman 21:20, 8 November 2006 (UTC)

Here I disagree on two points: a) I don't think 100% is actually being considered seriously anywhere,

2. It is - I am demonstrating it is a feasible goal here. No one has so far advanced any logical or factual arguements to discount it. Wind will be utterly insignificant, and relegated to a side show, unless the proponents of wind power wake up to the fact that it is perfectly possible to have 100% in terms of annual energy supply from wind. If wind proponents do not step up to this challenge, then entrenched vested interests will continue to push the unfeasible in the long term of fossil or nuclear power, and policy makers who are not technical will continue to dismiss it as a sideshow.Engineman 21:37, 9 November 2006 (UTC)

at least in the foreseeable future, precisely because it is so far away, but that is my opinion; and b) Opponents and critics of wind power frequently cite what I think is a specious argument, to wit, "wind has problems that mean that it can't provide 100% of power." Whether or not that statement is true (the answer is not true or false, but one of trade-offs), 

I disagree, it is demonstrably false.

it does not mean that wind could not provide substantially more with few problems. In other words, saying "wind has problems providing 100% of power" is a red herring often used to distract from the point that wind could be expanded considerably before intermittency (or other problems) became a serious issue.--Gregalton 08:20, 9 November 2006 (UTC)

OK I see your point, so I would say that it is, to coin a phrase, then it is a false red herring - becauaw wind does not have any more problems in providing 100% than say nuclear. In order to have 30% nuclear in UK we had to build the 2 GW Dinorwig pumped storage scheme, no other purpose than to help nuclear, and to install a large amount of off peak storage heating systems. And that links back to my point in para I have labelled 2 - unless this is exposed as a false red herring then the opponents will have achieved there aim in cnfusing policy makers.Engineman 21:37, 9 November 2006 (UTC)

I would, in all due respect, dispute the figures above about diesel and unreliability of large power stations. I do not know about the UK Sizewell B, but in Ontario, 1.2 GW is about 3.5-5% of peak demand of about 25 GW. While this would be a severe loss at peak demand, in many other instances it would be manageable (assuming not completely instantaneous)

The loss of Sizewell B, or any large power station, is completely instantaneous - as soon as the breakers open, and is entirely unpredictable and can therefore happen at any time - peak or not at peak - this scenario is typical to all power grids worldwide, in one form or another. All power stations are unreliable in that they can all immediately fail, totally and without warning. No matter how reliable a power plant is, it can still fail – maybe only once in 10 years, but that possibility is what determines the measures taken to cope with the intermittency, even if the power stations are highly reliable. The wind is intrinsically in these terms more reliable than a power station and the more you have the more reliable they become, simply because all wind turbines spread over a large areas can’t suddenly all stop at once.Engineman 21:59, 8 November 2006 (UTC)

Your point on sizing the backup for unreliability or instantaneous events (often the loss of the single largest plant) is good, and I had intended to underscore that wind is better on this point (losses occur gradually, except in the case of transmission line failure, which is true of most types of generation). That said, saying wind is "more reliable" is not very precise here - it's a different reliability/variability profile. Nuclear, for example, is reliable >90% of the time with little variability, but disruption events could take the whole plant offline (total failure); geographically spread wind has almost no probability of total failure, but much higher variability (and no ability to dispatch). In this sense, wind is quite reliably variable. Nuclear's reliability/variability profile also has weaknesses for certain uses (good for base, poor dispatchability). --Gregalton 08:20, 9 November 2006 (UTC)

OK I agree with your points here - but a matter of terminology I think. You can see what I mean....the sudden changes in supply due to 100% wind would be much less in UK say, and presumably any where else, than the sudden failure of a large unit. Slow changes, down to zero wind, can easily be coped with by the gradual starting up of existing fossil units, which will only need to be used a few days per year. If you work out the cost of this, using the published spark spread, it is very low - about -0.75p/kWh.

- there is 6 MW + of hydropower capacity. At any 100% wind scenario - which I assume to mean 100% of power is expected to come from wind, on average, meaning nameplate wind capacity would be 3.5-5X average daily demand and about 100-300X greater than current installed capacity - intermittency/variability would be massive. Backup diesel capacity for this would be enormously expensive.

Clarifiication. The back up in a 100% scenario comes from the existing fossil plant which are retained, diesels woud be used for only a small fraction of the total load on the grid and only for a few hours for any sudden change, as is standard practice in the UK and France, and the US. Diesel back up is widespread in the US - for exampel Cayhoga Falls substation has about 15 x 1.4 Caterpillare diesels installed - and there are 100s more across the US.Engineman 21:37, 9 November 2006 (UTC)

No it wouldn't be enormously expensive - not if you utilize diesels that have already been paid for as emergency generators for e.g. hospitals, offices etc, and which have to be paralellable in order for them to be tested. Since they are only used a few hour per year, the fuel cost is very low comparatively.Engineman 21:59, 8 November 2006 (UTC)

I don’t see where the 100 – 300x greater than current installed capacity comes from? The installed capacity of exisiting power stations on the UK National Grid, is about 70 GW say, and to entirely generate the total annual output of this system would need about 102 GWEngineman 21:59, 8 November 2006 (UTC)pk,

If using existing diesel plants, I would agree. To invest in extra diesel for this purpose, quite expensive. As for my 100-300X figure, very rough calculation for Ontario, based on the following: wind production 20-35% of nameplate capacity (you say 40% for UK, adjust as needed), existing nameplate about 1% of peak demand, some "extra" wind required to allow for variability. If current nameplate is 1%, 100X increase is conservative. --Gregalton 08:20, 9 November 2006 (UTC)I get it but it misses the point.Engineman 21:37, 9 November 2006 (UTC)

Don't get me wrong, much higher penetration than the current <1% nameplate capacity / peak demand should be easy, but 100% seems a ridiculous target, (I disagree on good grounds and I see no evidence to disprove my assertion Engineman 21:37, 9 November 2006 (UTC)particularly if diesel backup was to be considered. (sorry but you seem to be still missing my point - the bulk back up comes from the fossil stations already built. Only a small fraction needs to be diesel, and they ahve already been builtEngineman) Also, my understanding is that France uses primarily nuclear power, has low A/C usage, and given the low marginal cost of base load, diesel back-up may make sense; in different conditions, diesel may not be realistic, i.e. almost anywhere else.

Diesels are widely used for this purpose in the UK, and France and USA and I don’t doubt many other large grid systems. Denmark is about to start doing it.Engineman

Would you explain why you assert that 100% wind is a ridiculous target - what are your reasons for saying that? Diesel back up is not being promoted in the way you imply - if you look at the original paper which explains how the UK grid works, you will see that diesel is already widely used.

Why do you say that the intermittency would be massive? In fact it can easily be shown to be not so using a thought experiment - if you imagine sufficient wind capacity spread around the coast of the uk to generate 100% of units supplied to UK over the year, and consider wind patterns and the speed at which they propagate, (50 mph?) it soon becomes obvious that even with 100% wind the rate of change of the total output of all the turbines is in fact quite slow. Graham Sinden has studied the variability of wind turbine output and found it to be very low, by looking at the simultaneous wind speed variation of weather stations over the UK for the last 30 years. And you have to compare this with the rate of change of supply when Sizewell B trips in the UK. This is a loss of 1.2 GW in zero time, whereas the rate of change of 1% of the output of the required 102 GW of distributed wind power would only achieve this change over a few minutes in the worst case.Engineman 21:20, 8 November 2006 (UTC)

I think it is a ridiculous target at present because no-one is anywhere near that; capacity (to build the turbines and site), intermittency, and other issues compound it. (sorry but that strikes me as a very strange position, to have targets only based on what you have alredy achieved. by that token it would be absurd for Kennedy to have a target in 58 to put a man on the moon on the grounds that one hadn't even been put into orbit.Engineman 21:37, 9 November 2006 (UTC)I also don't believe that any one technology is likely to be appropriate for most grids, (well what other carbon free sourse is there?Engineman 21:37, 9 November 2006 (UTC))except perhaps hydro where the appropriate geological conditions obtain (pretty rare, but no unheard of).

That said, 20% in many jurisdictions should not be problematic, and considerably more in many others. If you stick at 20 % then policy makers will say, this is a side show, we are going to go totally nuclear or clean coal, niether of which is viable in the long termEngineman 21:37, 9 November 2006 (UTC)) That is entirely respectable and would represent a massive increase over existing capacity, a significant contribution to a reduction in pollution and global warming, energy security, etc. As for the figures on the UK's variability of wind, I'm not familiar with this study. Every study I have seen for other jurisdictions suggests that variability does increase, and very significantly (massively?) at high penetration levels, even for fairly large geographic areas; ( can you cite any study which shows this?- its plainly untrueEngineman 21:37, 9 November 2006 (UTC))current storage technology (and costs associated) mean that installing storage specifically (you don't need storage - you install EHVDC cables and import and export power to neighbouring areas to suit - as does Norway to Germany and Denmark, and the Dutch connection currently being built to FranceEngineman 21:37, 9 November 2006 (UTC)) to cope with intermittency of wind raises the costs significantly for projected high penetrations. (this is simply not true in any significant senseEngineman 21:37, 9 November 2006 (UTC)) Over the longer term, I grant that this may change. --Gregalton 08:20, 9 November 2006 (UTC)

That said, I agree with the opening point in this section, even if for different reasons. Intermittency is potentially a very big problem at high penetrations, but penetration is below 10% in most places, and only 20-odd percent in Denmark. This subject is the bogeyman of wind power - much feared, rarely seen.--Gregalton 23:00, 7 November 2006 (UTC)

My first question is what is the capacity factor of existing costal wind turbines in the UK?

About 40%.....Engineman 23:19, 8 November 2006 (UTC)

In the US, the best wind farms typically operate at 40% capacity factor.  Compare that to a conventional steam generator which typically have a 80-90% capacity factor.  Even with many, many turbines distributed over a large geographic area, a 70% capacity factor would be quite impressive. 

Don't undertstand the logic here? About 102 GW of wind at 40% roughly replaces the total annual output of the UK grid, with its peak load of about 60 GW - what's the problem and where does the 70% capacity factor come from?Engineman 23:19, 8 November 2006 (UTC)

Another thought experiment: imagine 102 GW of wind replacing average annual load of 40 GW (approximately) at the 40% capacity figure, with base (minimum) demand of 30 GW, assuming half of peak. Wind might have variability between 20-60 GW output, even with good spatial diversity (feel free to adjust assumptions), as wind speeds over the UK have some correlation. Unfortunately, that output is uncorrelated with demand/load. So there would be instances (albeit infrequent) where wind is 40 GW short (max demand minus minimum output), and there will be instances where wind output is 30 GW above system needs. The swing from one to the other may not happen in a single day, but it is still a wide range. Of course, load shedding, storage, power export, and other solutions are possible (including simply disconnecting the wind turbines for a period), but they all involve additional costs or lower revenue; the higher the proportion of wind, the higher these costs. This is, of course, simplistic analysis, but it does give an indication of the potential scale of the issue. (Even if wind's variability can be reduced to 30-50 GW output, which strikes me as low, the range is still 30 GW short / 20 GW over). Even if the system is quite flexible, it implies a large additional capacity to deal with the surplus/deficit, which (with current tech) would raise the overall cost of wind substantially.--Gregalton 10:15, 9 November 2006 (UTC)

That is a good summary of the issues. But the cost of EHVDC cables is very low nowadays - the longest one currenlty is 1500 kM, so all one does is to export the surplus and re-import it as required. Even without wind power, the cables will have significant savings simply due to the reductino in total capacity. If you don;t like cables, there are numerous other forms of cheap storage - off peak heat, deffereing or advancing fridges etc.Engineman 21:37, 9 November 2006 (UTC)

Gregalton, thanks for the above as it very clearly states the issue. If you look at Graham Sindens paper you will see that it is in fact very rare to have the 102GW of notional turbines operating flat out for very long, so the period when you have to do something with the excess, and the quantity is quite small comparatively speaking.

Any short term over generation, could easily be dealt with in a number of very cheap ways. For example, install a 3 kw resistance water heater in each of 20 million UK homes connected by a frequency sensitive switch. That would give 60 GW of instantaneous storage or load deferral. About 5 million UK homes already have 10 kW storage space heaters and these could be similarly flexed - at present they are on dumb timers, but again they could easily be switched to cascaded frequency control ( so they all come on and off in progression). That gives you another 50 GW of instantaneous storage for several days. By the way, these were only introduced in the 60s to cope with the then percieved intermittency and inflexibility of nuclear power, along with the 2 GW of pumped storage at Dinorwig/ Ffestiniog. See also Frequency Service and Reserve Service

Then we have David Hirst's technology of advancing or deferring fridges, freezers etc which gives another 10 GW and this is just some cheap electronics in a plug.

There is also the issue that for 102 GW of wind, Sinden shows that there is always some wind generation somewhere, so infact it some portion of wind counts as 100% reliable basedload, meaning we can retire some existing plants with the attendant savings.Engineman 22:42, 13 November 2006 (UTC)

Another question I have is why would a 1.2 GW unit trip cause under-frequency load shedding?

Well it just does - lose output and the frquency must start to fall as soon as load exceeds generation....National Grid frequency service loads are then automatically shed in direct proportion to the fall in frequency...Engineman 23:25, 8 November 2006 (UTC)Engineman 23:19, 8 November 2006 (UTC)

While this is a large unit, if the loss of this unit is the most severe contingency, the power system should be carrying sufficient operating reserves to suffer the loss of the unit without the loss of load.

That is simply not the case. The UK and the US national grid has certain large users who are contracted and qutie happy to have there load shed under just such an eventuality They find it cheaper than spinning reserveEngineman 22:42, 13 November 2006 (UTC).User:Engineman|Engineman]] 23:19, 8 November 2006 (UTC)

If the UK doesn't require this type of operating procedures on their system, my guess is that the variable nature of wind generation without sufficient operating reserves would result in frequency deviations, possibly resulting in load shedding. Doublee 22:56, 8 November 2006 (UTC)

Errrr that is the whole point of what I have been saying- the UK system is designed to do just that - load shed as Hz falls. Look up Freqency Service and Reserve Service. User:Engineman|Engineman]] 23:19, 8 November 2006 (UTC)

My understanding is that the profile of wind power generation (the power curve) is also problematic. More specifically, wind's median power output is significantly lower than the average, because power output rises geometrically with wind speed (put another way, periods of high wind contribute more to the average output than average wind periods). Even over a large area, even with 30-40% average capacity, the base component would have to be lower. For example, I have seen the figure of 20% (of nameplate) being used as capacity contribution fairly frequently; while this is probably conservative, this would mean far more wind would be needed to provide base load than the 25-40% capacity factor indicates. Not much of an issue at low-to-medium penetrations, a very big issue at high penetrations. When I look at the output of wind farms in Ontario (www.ieso.ca, look at hourly generation data), this is supported: lots of periods of output at 10-20% capacity, then some periods where 60-80%, resulting in the average capacity; unfortunately, the peak output tends to be at times of lower demand (night-time), and the lower output at times of higher demand (daytime and summer). That said, the 10% appears pretty reliable. (Usual disclaimers on this data, Ontario is not representative, not enough geographical diversity, not enough historical data, this is not a proper statistical study, etc., etc.)--Gregalton 08:20, 9 November 2006 (UTC)

Again I think you have missed my point a bit....if there is no wind, you simply start up the old power stations you have already built. They don't cost much to keep on standby.Engineman 21:37, 9 November 2006 (UTC)

Engineman, a few quick points...

1) It would make it much more like a discussion, and readable by others, if you could interject as separate paragraphs rather than editing within sentences. It is no longer possible to figure out what's what here, and may not be useful to anyone.(I was tempted to just revert to the previous version, just so it would be readable - if you were able to edit back so that your comments are separate, that would be helpful.) I think the discussion should also attempt to determine what meets the standards for inclusion in the main page, and we may have gotten away from that.

2) I think we are departing from different reference points and different assumptions. My background is economics/public policy/finance, areas where the cost and revenue matter. For wind power, the criticism I see and hear frequently is that a) it is not viable (or very expensive) at high penetrations and therefore b) wind is not a complete solution. As I've stated, I think part b is specious (no other form of energy is held to this test). Part a requires more data and experience than currently possible, and depends on market structure and a number of other factors, but is also many years out; that said, there are serious issues.

3) There are a number of credible studies (i.e. by system operators) stating clearly that there are minimal issues at levels up to 20%. See, for example, http://www.ieso.ca/imoweb/pubs/marketreports/OPA-Report-200610-1.pdf. In this study, and with existing systems, however, going substantially further (here to about 33%) would cause some problems (too much wind power when not needed seems to be biggest issue, but based on existing generation profiles); you asked for a citation, here it is. I have not seen any studies suggesting going above 50% would be easy or cost-free, but look forward to seeing citations; I have seen studies that "show" that costs grow substantially at higher levels. (And note: if wind annual capacity is 40%, the penetration level needs to be 2.5X higher to meet annual consumption, and I certainly haven't seen studies on implications of 250% penetration levels)

What frustrates me is that people talk about "problems" which implies it is unknown or insurmountable as to how to deal with it. I claim that the alleged problems with high penetrations are simply technical issues that can be dealt with in known ways at low cost.

I did not intend for it to imply it is unknown or insurmountable, and don't think that is the meaning of "problems." If you prefer, "challenges." And, what I question is the extent to which these are technical issues that can be done at "low cost." How much? My point is that the costs are unknown, and that the solutions may make high penetrations uneconomical.

I don't know of any citations looking at 100% apart from my own very rough and ready (never the less I believe robust) attempts. But where are the citations to show it is not possible?

This does not require much research. Search google for "wind power maximum penetration limit", lots of hits. To pick at random one study, see http://www.ucc.ie/ucc/depts/civil/staff/brian/EWEC03.pdf . For Ireland, they find that approximately 60% penetration (very rough figure) "the curtailment of the last wind turbine is such that it will operate for only a few hours per year during periods of maximum demand. Clearly this would be uneconomic" (My bold). (To explain, curtailment would be points at which wind turbines would no longer be producing electricity for sale - they may be physically shut down or spun with generator disconnected or by other means). Of course, plenty of potential solutions exist, Ireland may be a special case, etc, but it remains a challenge. You can also look for deCarolis and Keith, "The Costs of Wind's Variability: Is There a Threshold?", The Electricity Journal, which has a more theoretical approach to looking at the costs. Hence, the prima facie case exists that above some level, wind may be uneconomic, even if technically possible.--Gregalton 07:35, 13 November 2006 (UTC)

Your own rough and ready calculations are interesting, but this is original research. While it's interesting, it's distinct from verifiable outside expertise. Apart from that, I personally don't find it to be "proof" or not subject to dispute (for example, maintaining all existing plants unused would only cost 0.2 pence / kWh? If current production costs, for example, 4 pence, to me this would imply that fuel makes up 95% of current operating expenses.

Gregalton - look up Spark Spread - published figures show that the profit a power station makes is £7-9 / kWh. Revers that back to how much they would have to be paid, if they didn;t run, and its about 0.75p/kW h. There is no dispute - Spark spreads are widrly published.Engineman 22:52, 13 November 2006 (UTC)

Sounds high, and just not convincing - to me). At any rate, this is not the place to question your numbers, or for original research, but to attempt to determine what is "encyclopedic" enough - i.e. verifiable - to merit inclusion in this main page. Others should weigh in, but I return to the main point: the claim that 100% wind generation can be achieved economically is not proven or verifiable. Conversely, the claim that 20% is believed to be feasible is, if not proven, sufficiently credible. --Gregalton 07:35, 13 November 2006 (UTC)

4) In my view, the evidence that 20% penetration causes no major issues is reasonably credible, and 20% is not a "side show" - would be more than existing hydropower worldwide, and probably nuclear. Since world penetration is ca. 1%, penetration can be increased significantly in most jurisdictions before this issue becomes relevant (pace Denmark). It will also take a long time to get to 20%, and technology and experience will develop further after that point, and increases beyond that may prove economical and reasonable. Denmark will hopefully show the way. [Note that Denmark's "20%" penetration is in fact only 1-2% on the international grid that they depend on so heavily. Kerberos 17:15, 16 November 2006 (UTC)]

5) But the evidence that 100% can be done economically and reasonably is not "proven", as you have asserted, or at least, I haven't seen it. I do not see the statistical evidence that suggests there would only be a few days per year with too little/too much wind (even completely uncorrelated wind resources have this problem).

Look at Graham Sindens work in the UK. Oxford Universitey and the recent UKERC study. But in any case the exact number of days doesn't really matter since the costs of using the exisitng power stations as back up is so low. See Spark spread and Triads.

I do not see the financial numbers behind the solutions. I see issues with, for example, exporting large amounts of wind - to where? Countirs where it is not windy at that time. Engineman 12:12, 12 November 2006 (UTC) Will they pay? Well Germany and Norway have been doing it for years. Engineman 12:12, 12 November 2006 (UTC)How much? Do they have wind too? at these large distance they are largelyuncorrelatedEngineman 12:12, 12 November 2006 (UTC) The storage solutions, from what I have seen, are either not there or quite expensive domestic hot water and domestic space heating - happens in New Zealnd alreadyEngineman 12:12, 12 November 2006 (UTC) . To people financing wind farms, or paying for the cable, or running the systems, these issues matter a lot. Like the poeple who are payoing for the Dutch - Norway interrconnector, and the 20 year old Mid germany to Norway, or the UK France interconnector?Engineman 12:12, 12 November 2006 (UTC)

Ok I'll agree I haven't proven it in that strict sense - but overall I think I have shown it pretty unlikely that economic solutions cannot be found. Massive inter regional power flows already occur for other reasons.

6) Thanks for the information on diesel backup. This appears to be more significant than I thought.--Gregalton

07:28, 10 November 2006 (UTC)

Greg - thanks for the points. I'll re-edit this in the next few days.

To sum up in reference to the header: Intermittency of wind is potentially a big problem at high penetrations but the problem is overstated at low-to-medium penetrations. Since few grids have penetration above 10%, the problem of intermittency is overstated at present, and for most reasonable projections about wind penetration in the medium term. --Gregalton 08:24, 9 November 2006 (UTC)

Can you give any quantitive reasons to qualify and justify the assertion that it is a big problem? To put it into context,when the nuclear industry started in the UK in the 60s, some would have said that the inflexibilyt of nuclear would create BIG PROBLEMS. They were solved by a) building Dinorwic, 2 GW of flex plant, b) the cross channel interconnector - 2 GW c) massive expansion of night storage heaters.

I beleive I have disproved this (potential problem at high penetrations), becasue at 100% penetration, the max rate of change is less than that caused by the exisitn power stations.Engineman 21:37, 9 November 2006 (UTC))

Minnkota Power Cooperative, Inc. headquartered in Grand Forks, North Dakota, USA, has been successfully utilizing a load management system based on ripple control since the late 1970s.

What began as a simple tool to control peak demand during the winter – the share of electric heating loads on the Minnkota system is substantial – turned out to be a highly reliable and cost-saving instrument for the utility in recent decades. The primary driver for Minnkota’s decision to utilize load management by ripple control was the mature and well-proven technology, as well as the guaranteed signal reception at the customer’s home, school, farm or business where the various switching commands must be executed precisely.

Today, Minnkota is actively controlling a 40 percent share of its wintertime load during peak-use conditions, typically when economically priced power is not available to serve the off-peak loads. The load management system allows Minnkota to offer a competitive wholesale power rate to the 11 member-owner distribution cooperatives in eastern North Dakota and northwestern Minnesota.

Hours of control have increased from an average of 30-40 hours per heating season in the past to approximately 400 hours a year. Customers are strongly encouraged to have properly sized and operational alternate fuel backup heating systems to carry them through control times.

As a service to off-peak customers, Minnkota displays the actual status of the load management system on its Web site, www.minnkota.com. Off-peak heating remains the best energy value in the Minnkota service area.

Minnkota is sourcing its Load Management equipment from a variety of highly reliable suppliers.

Facts:

Area of Supply: 34,500-square miles Number of customers: More than 117,000 Summer Peak Load: 500 MW Winter Peak Load: 650 MW Own Generation Capacity: 528 Third Party Generation Capacity: 16

I was not referring to max rate of change, but others can decide whether this issue has been "disproven". --Gregalton 07:28, 10 November 2006 (UTC)

Due to unawareness on how to reply in a wiki thread, this thread is too difficult to follow. Please use new lines and colons (one more than the previous comment) in order to provide the indentation that makes a thread readable. Otherwise, you will have wasted your time trying to communicate your ideas. Skyemoor 12:47, 10 November 2006 (UTC)

I would suggest moving this entire section on intermittency and variability to a new page, leaving just a summary here of the main issues. It is a complex topic and appears to be important enough to merit the change. It would also reduce the amount of editing on a fairly important page, and have the more detailed editing work going on there. Any opinions? --Gregalton 19:01, 12 November 2006 (UTC)

Good idea I think. Engineman 10:27, 14 November 2006 (UTC)

I'm fine with that, as it involves any intermittent power source, not just wind. One further point; if overproduction is an issue at times, the excess could be used in ramped-up hydrogen production. Skyemoor 10:37, 14 November 2006 (UTC)

Pricing limitations?

I'm not sure what this statement means, "Many grids also use energy pricing to influence supply and demand (increasing prices to encourage increased supply and lower demand), 'but pricing solutions are incomplete solutions due to different time frames needed to find "market pricing" solutions and the operation of the grid.

"Real time" spot pricing can be one effective means to limit demand during low generation points (i.e. wind speed falls off, skies become overcast in a region, drought reduces hydropower rates/reserves, etc). Hence, the price could change for an hour, a day, a week, and so forth. It can be tied in with DSM/Load Shed management systems to reduce demand (i.e., electric hot water heaters go to 115F instead of 125F, A/C units go to lower duty cycle, etc). Skyemoor 12:32, 18 November 2006 (UTC)

The statement was intended to convey that no system uses pricing alone to ensure reliability, due to lags in adjustment to prices, etc. In other words, even the most "market-oriented" grid pricing systems are ultimately highly regulated. In comparison to, say, the banana trade - if Company X imports more bananas in week Y than anyone wants to eat, the bananas spoil and X is out the money. Contrast with electricity - systems exist to ensure that everyone participating follow quite precise rules, that are enforced using non-price mechanisms.--Gregalton 15:05, 18 November 2006 (UTC)

I'm still not sure I understand what is trying to be communicated. See if my markup begins to approach what you are saying. (and please use indentation in the Talk page, using one more colon than the person before you). Some interesting links on spot pricing are;

• Spot Pricing of Electricity and Ancillary Services in a Competitive California Market http://eetd.lbl.gov/certs/pdf/46944.pdf
• Pricing Electricity Calls http://www.ucalgary.ca/~sick/Research/ElliottSickSteinElectric5.pdf
• Filtering and Forecasting Spot Electricity Prices in the Increasingly Deregulated Australian Electricity Market http://econpapers.repec.org/paper/utsrpaper/63.htm
• Pricing Electricity Derivatives Under Alternative Stochastic Spot Price Models http://csdl2.computer.org/comp/proceedings/hicss/2000/0493/04/04934025.pdf

Skyemoor 10:18, 19 November 2006 (UTC)

I have no difficulty with the phrasing you used in the page. Again, the issue I'm trying to address is simply that a pure pricing solution is insufficient, and even so-called "deregulated" markets have quite specific rules for participants. In economic terms, a "market-clearing" solution might occasionally not be found without intervention, and is effectively enforced. Perhaps this is an issue that does not need to be addressed here at all.--Gregalton 11:26, 19 November 2006 (UTC)

There will not be one overall solution, but a set of solutions (i.e., storage, DSM, pricing, etc). Skyemoor 12:12, 19 November 2006 (UTC)

Cost of export transmission capacity

There is an assertion in the "maximum penetration" section that export transmission capacity is "cheap". This seems to me to need a reference or costing as a function of scale. For example, Ontario-Quebec link gives one instance of a 1,250 MW link to be built between Ontario and Quebec will cost over $800 million (Canadian), or approximately $640,000 per MW. Now, I do not make any assertion that this is the cheapest possible, or comparable, and it is only one datapoint. But "cheap" clearly needs to be defined better. Note that if wind power costs approximately $1-$2 million per MW of nameplate capacity, it would also seem to not be cheap relative to the cost of generating capacity for wind, it could potentially affect the economics of wind quite substantially.--Gregalton 21:37, 21 November 2006 (UTC)

One question is why was the link built in the first place ? presumably a case in terms of avoiding building more power stations in either grid, and sharing diversity savings. So the same applied to any interconnection - there are large savings availalbe by joining up grids in terms of reduction in total capacity and spinning reserve. Once built they aid the penetration of wind power.

If they are built purely to help wind power then the above beneftis acrrue.

Also, the $640,000 per MW isnet to be compared to each MW of installed capacity, but the surplus that has to be exported at peak, which will only be a fraction of the installed capacity of the windfarms.Engineman 20:51, 21 November 2006 (UTC)

I am not trying to deny reasons why the link was built in this case, and there are undoubtedly good reasons to do so; I'm simply attempting to determine whether, in the context of an NPOV article, stating that building export transmission lines is "cheap" is justifiable. It's rather vague and does not sound convincing.--Gregalton 21:37, 21 November 2006 (UTC)

I also understand there are many, many benefits to joining up the grids, but we know it does not happen all the time - presumably one reason is that it is not always (sufficiently) "cheap", or justified by the benefits. As far as your second point (to be compared to the export at peak), I agree: but what scale of export capacity, at what cost, in the scenario mentioned.--Gregalton 21:39, 21 November 2006 (UTC)

Fair point.... I guess I am saying that in the context under discussion, interinking of grids is highly economic ie a mix of the appropriate amount of cables will improve the overall economics of wind. Have a look at Project Genie.....Engineman 19:40, 24 November 2006 (UTC)

I am not arguing that the appropriate amount of cables would not improve the economics of wind; if interlinking the grids were free, it would be an easy decision. The question I am trying to get at is whether the cables themselves are economically justified. You have asserted they are "cheap"; I'm not sure that is verifiable.--Gregalton 23:30, 24 November 2006 (UTC)

Gregalton - thats a hard one to answer - but presumably the 1500 km EHVDC running up Africa, bringin power from a hydro resource to a copper mine is justifiable economically so presumably that would apply elswhere - likewise the UK cross channel link? 86.137.143.120 18:47, 25 November 2006 (UTC)

A separate point: I'm not convinced your most recent edits are neutral or verifiable, let alone factual accuracy (to my knowledge, there are no 660 MW turbines). In addition, you've changed the meaning and context of the text enough that I'm tempted to simply revert to the previous version. Grateful you look at your edits again, in general.--Gregalton 23:30, 24 November 2006 (UTC)

Fine - I've revisited them hopefully now neutral.

Gregalton - I was referring to the 660 MW steam turbines on the UK natinal grid?86.137.143.120 18:47, 25 November 2006 (UTC)

In particular, you refer to reliability and variability as if they were the same thing. Again, a wind plant might be reliable, but extremely variable (no sudden total loss, considerable swings in output), but other types of generation may be invariate (little change in output) but have lower reliability than wind (more likelihood of total loss). It's not that one is bad, they just have different implications. These need to be clarified to get NPV.--Gregalton 23:30, 24 November 2006 (UTC)

I think we are slightly at cross purpose here - I am saying that for a large penetration, and hence a large number of wind turbines, the net output is very reliable - it cannot in agreggate change nearly as quickly as iether a tv load pick up, or the loss of two large plants.86.137.143.120 18:47, 25 November 2006 (UTC)

I would agree with Gregalton in that there is only focus on the individual plant reliability. Due to the distributed nature and sheer number of turbines, wind farms will always give some output. However, the additions severely minimize the dispatchable nature of traditional power plants versus the fact that wind farms cannot be dispatched AT ALL. The output is variable, and while can be predicted, since when are weather forecasts accurate in a day ahead/next 12 hour timeframe? The loss of 2 plants simultaneously (1200 MW) in North America is considered a double-contingency and therefore does not require reserves to be carried for it. Also, a 660 MW plant contingency does not necessarily require 660 MW of reserves to be carried. It most likely will be less as the governor action of the units on-line with spinning reserve will arrest the frequency decline at around 59.5 Hz (in North America) You don't need 660 MW of spinning reserve to keep frequency above 59.5 Hz. I don't agree with the edits and think they should be reverted. As an operations and planning engineer with a US utility, the discussions so far tell me that no one contributing to these discussions works in operations or planning. Many of the arguments are theoretical and don't jive with how the power system is operated and assumes that DSM is guaranteed and very prevalent. DSM is a solution, but in the US, you can't require people to be on DSM.Doublee 15:54, 25 November 2006 (UTC)

Doublee - I did not say that a large quantity of wind turbines produces a despatchable output. I am pointing out the conventional plant can easily follow the slowly changing aggregate output of a very large number of turbines - this is no more than a power system already does.

Why do you only quote a 12 hour forecasing time frame? Weather forecasting is pretty accurate for wind speed 12 hours ahead, but obvously you can refine your forecasts as time goes on, until eventually you are forecasting 6, hours, 3, 1 hour, then 15 minutes, 5 minutes etc. What's the difficulty? That's what our UK already grid does - it is well known National Grid study the tv guide and make adjustments in readyness for predictions that are only a few minutes / seconds ahead for say half time in a foot ball match.

Regarding DSM - it is not compulsory in the UK, where my comments apply - there is a market mechanism and people are paid to make up to 2 GW of DSM available - autoamtically switchable load and diesel engines- this is extremely cheap and could be readily extended. It is my understanding that there is DSM in the USA as well? I used to work for Caterpillar and there were a large number of diesel sets installed on US substations for this purpose Cayhoga Falls was one I recall where there were about 10 x 2 MW sets. Pesumably in response to some market mechanism?

I note you have wind turbines as being not dispatchable AT ALL. I fully understand that and have not said or implied that. So I assume you are misinterpretting my point somewhere along the line.Engineman 21:34, 25 November 2006 (UTC)