Intermittency of Wind Power Generation

Jim Martin

I get the impression that the more electricity that is transmitted by bigger grids, the more energy loss is encountered so is not the whole thing a total waste of time?

djpbarry

Jim Martin wrote: »

I get the impression that the more electricity that is transmitted by bigger grids, the more energy loss is encountered so is not the whole thing a total waste of time?

Transmission losses are certainly an issue, but it's not an insurmountable problem. For example, high-voltage direct current (HVDC) transmission systems incur far lower losses than AC transmission over long distances, although the up-front capital cost is higher.

Capt'n Midnight

Jim Martin wrote: »

I get the impression that the more electricity that is transmitted by bigger grids, the more energy loss is encountered so is not the whole thing a total waste of time?

On longer lines they use higher voltages to counteract this

losses are a few % rather than a few ten's of % , but even then it's usually cheaper to transmit surplus power than to generate it locally

power lost due to heating is I squared R, so at light loads the losses are lower and it's at peak demand that you have peak losses and at that point power is most valuable

Chloe Pink

Rather than address individual posts, I am providing a link that looks at the "back up" needed for wind turbines.

The link is from Eon UK who are related to Eon Netz, the German grid operators and the largest wind developers in Europe.
Eon UK’s submission to the House of Lords Select Committee of Economic Affairs on the Economics of Renewable Energy, comments on the backup needed for wind in the UK, all 92% of it:

http://www.publications.parliament.uk/pa/ld200708/ldselect/ldeconaf/195/8061708.htm

It is a short submission and well worth a read but points 8, 9 and 10 look at the backup specifically and describe the reliability of wind versus that of conventional power stations, we're talking about 8% versus 95% respectively.

Chloe Pink

The “Tyndall Centre Technical Report 30, July 2005 Conclusion 5, Security of decarbonised electricity systems” refers to the back up plants needed for wind turbines:
"We observed that wind generation has a relatively small capacity credit. At lower levels of wind penetrations the capacity credit of wind generation is found to be about the same as the average load factor of wind. However, as the level of wind penetration rises, the capacity credit begins to tail off. That is why in order to maintain the same level of system security a significant capacity of conventional plant will still be required.
However, these conventional plants will be required to run either occasionally and/or at part load when shortages of supply are likely to occur due to a low total wind power output. Considering that conventional plants at full load are the most efficient and generate the lowest amount of CO2 emission (per electricity produced) such occasionally and/or part-loaded plants will be less utilised and/or produce more CO2 per electricity produced."

Chloe Pink

Hugh Sharman is principal of international energy consulting and broking company Incoteco (Denmark).
The title of his Telford Gold Award winning paper on “Why the UK should build no more than 10GW of wind”. explains why there is a limit to the amount of wind capacity we should have in the UK:

http://www.ref.org.uk/images/PDFs/sharman.ice.pt2.pdf

Chloe Pink

The wind forecasts and out-turns can be seen three days at a time at this link under the graph 'Wind Forecast Out-turn':

http://www.bmreports.com/bsp/bsp.php#wind_fc_outturn

Chloe Pink

How is wind looking now as a sensible form of power generation?

Macha

Chloe Pink, please try to formulate your arguments into fewer posts, rather than multiple postings.

I don't think anyone here is advocating a national grid run off 100% wind. Rather, wind will have to be paired with more dispatchable renewables like hydro, biogas, tidal and solar. Increasing the size of the grid and a dispersed pattern of renewable generating stations will also assist in increasing the penetration of renewables.

SEAI held a conference on this subject last Friday in Dublin:

http://www.seai.ie/News_Events/Press_Releases/Pathways_to_2050_release.pdf

Chloe Pink

My apologies for the multiple postings, I was simply trying to provide some hopefully helpful information in manageable chunks.

What is the point of backing up / pairing one renewable with another dispatchable renewable, why not just have the despatchable renewable?

For example, why have tidal backing up wind, why not just have the tidal; if the tidal is generating, we still need to store its output if the wind decides to blow in which case we're back to the problem of storage.

And if the wind isn't blowing at night, the sun won't help us unless we've stored it from the day before.

And which valleys should we flood to increase our hydro storage capacity?

Capt'n Midnight

Chloe Pink wrote: »

It is a short submission and well worth a read but points 8, 9 and 10 look at the backup specifically and describe the reliability of wind versus that of conventional power stations, we're talking about 8% versus 95% respectively.

it's nothing to do with reliability - 48% of US nuclear power stations have either been shut down before planned or had unplanned outages of longer than a year.
you are talking about needing 15% extra capacity to cover for supposedly baseline nuclear

wind power is very reliable, even if a few turbines fail you still have most of the available power

what isn't as reliable is the wind but even still you are claiming that wind can be relied upon to provide 8% of nameplate capacity, and when you consider that the average power from a wind farm is 32% of its maximum capacity what this really translates to is that we can rely on wind farms to provide a quarter of their capacity as baseline.

add in pumped storage and giving major industrial users discounts for reducing demand when asked means you don't need quite as much stand by power

Chloe Pink

Capt'n Midnight wrote: »

what isn't as reliable is the wind but even still you are claiming that wind can be relied upon to provide 8% of nameplate capacity, and when you consider that the average power from a wind farm is 32% of its maximum capacity what this really translates to is that we can rely on wind farms to provide a quarter of their capacity as baseline.

Firstly, I'm not claiming anything, I am pointing to information provided by experts in their field, in this case EON UK and they are quite explicit in what they say:

"On this basis, if the UK required, say, 40,000MW of wind capacity to meet its renewable target by 2020, only 8% of this renewable capacity (3,600MW) could be relied on to meet winter peak demand. This would avoid the need to build 3,600MW of new thermal plant but the remaining 36,400MW of renewable capacity would need to be "backed-up" by thermal plant to meet winter peak electricity demand in 2020."

http://www.publications.parliament.uk/pa/ld200708/ldselect/ldeconaf/195/8061708.htm

I do not see where they say that "we can rely on wind farms to provide a quarter of their capacity as baseline" as you suggest. Assuming you mean 'base load' when you say 'baseline', this would indicate that wind turbines are providing a quarter of their installed capacity, all the time.
This is not the case, the load factor of wind turbines is their output provided over a year as a percentage of their total installed capacity; in the UK, this is approximately 25% (not 32%) i.e. over a year, 100MW of installed wind capacity would yield 25MW. This means that sometimes this 100MW of installed capacity would yield only a few percent of its installed capacity and at others nearer to 100 percent of its installed capacity but not that it yields 25MW all the time.

Lenny Lovett

djpbarry wrote: »

Wind generation can be forecast up to one day in advance with over 90% accuracy. Same day forecasts are ∼94-95% accurate.

http://www.eirgrid.com/operations/systemperformancedata/windgeneration/

To be fair most wind farms are situated in areas where there is nearly always sufficent wind speed to rotate and, let's face it, the number of days that most areas in Ireland do not have sufficent breeze is very low.
.

mgmt wrote: »

Tell me you're joking???:eek:

You cannot rely on wind power. Full stop.

Do you want to live in a world full of brownouts and blackouts?

I doubt anyone relies on it totally but tbf it's not impossible. We use 50kwh wind turbine for one of our factories and it has very pleasantly surprised us in that it has never failed us yet. Granted we are near the coast but nonetheless on calm days there is still sufficent generation. We also supplement it with pv cells and use solar water heating. The entire system is well on target to have paid for itself over three years. So it's has been an excellent investment... And I was very skeptical prior.

The Nipp wrote: »

hospitals or anyone who needs 100% reliable power will have some form of expensive UPS installed.

Yes. we have a UPS system but rarely require it.

While "saving" generated electricity in a battery system is workable a more useful way is to tie in wind generation with hydro electric and use spare generated electricity to power pumps to fill reservoirs that will in turn power the hydro turbines. I'm not explaining myself very well - it's been a long day... !

Chloe Pink

Lenny Lovett wrote: »

To be fair most wind farms are situated in areas where there is nearly always sufficent wind speed to rotate and, let's face it, the number of days that most areas in Ireland do not have sufficent breeze is very low.

To be fair, we are discussing industrial wind turbines as part of a country's energy strategy i.e. 2MW plus and 100 metres high plus.
But yes, wind turbines do turn for roughly 80% of the time but that doesn't mean that they're generating at their installed capacity.
And indeed there are only a few days when wind is so low across all of a country that barely any electricity is generated from wind turbines but these days, none the less, occur.
And it is for these reasons that wind turbines need backup generators.

Interestingly, the wind forecasts do not appear to be 90% or 94% or 95% accurate on 'Wind Forecast Out-turn' graphs at this link:
http://www.bmreports.com/bsp/bsp.php#wind_fc_outturn

I doubt anyone relies on it totally but tbf it's not impossible. We use 50kwh wind turbine for one of our factories and it has very pleasantly surprised us in that it has never failed us yet. Granted we are near the coast but nonetheless on calm days there is still sufficent generation. We also supplement it with pv cells and use solar water heating. The entire system is well on target to have paid for itself over three years. So it's has been an excellent investment... And I was very skeptical prior.

I am interested to know how someone could rely on wind power alone and have an on demand electricity supply; are you willing to expand on this concept?

I am also interested in your investment versus payback costs if you are willing to share them as three years seems pretty swift by all accounts.
Are you on or off grid?
If you are on grid, do you feed any of your electricity from your renewables back onto the grid and if so do you get a good rate for this electricity?
If you are on grid, do you use any electricity from the grid and what percentage of your electricity usage is from the grid and what percentage is from your renewable generators?

Also you state, "nonetheless on calm days there is still sufficent generation". Sufficient generation to do what?

Yes. we have a UPS system but rarely require it.

While "saving" generated electricity in a battery system is workable a more useful way is to tie in wind generation with hydro electric and use spare generated electricity to power pumps to fill reservoirs that will in turn power the hydro turbines. I'm not explaining myself very well - it's been a long day... !

Indeed, if we had bountiful storage capacity, wind turbines begin to look a little better but where are all these reservoirs going to be? And transfer losses still need to be taken into account?

djpbarry

Chloe Pink wrote: »

Firstly, I'm not claiming anything...

You’re claiming plenty – pointing at the sources you’re posting and stating “hey, I’m just telling you what these guys are saying” isn’t going to wash.

Chloe Pink wrote: »

Interestingly, the wind forecasts do not appear to be 90% or 94% or 95% accurate on 'Wind Forecast Out-turn' graphs at this link:

Over what time period? 3 days? Is that statistically significant?

Chloe Pink

djpbarry wrote: »

You’re claiming plenty – pointing at the sources you’re posting and stating “hey, I’m just telling you what these guys are saying” isn’t going to wash.

What would you rather I did, make stuff up?

I would rather not to be misquoted please; where have I written the following words:
“hey, I’m just telling you what these guys are saying”?

I have written:
“I am pointing to information provided by experts in their field, in this case EON UK and they are quite explicit in what they say:

"On this basis, if the UK required, say, 40,000MW of wind capacity to meet its renewable target by 2020, only 8% of this renewable capacity (3,600MW) could be relied on to meet winter peak demand. This would avoid the need to build 3,600MW of new thermal plant but the remaining 36,400MW of renewable capacity would need to be "backed-up" by thermal plant to meet winter peak electricity demand in 2020."

http://www.publications.parliament.u...95/8061708.htm”

Do you have evidence contradicting EON UK on this matter?

djpbarry wrote: »

Over what time period? 3 days? Is that statistically significant?

The same point could have been made regarding your link which also only shows information for 3 days at a time (unless I have missed something): http://www.eirgrid.com/operations/systemperformancedata/windgeneration/
The sensible approach seems to be to keep an eye on the graphs every now and again. Certainly right now, Eirgrid’s forecasting is not looking 90% or 94% or 95% accurate; the "Show/Hide Tabular Data" button at the bottom left of these graphs is quite useful for looking at this.

Anyway, I do regard 3 days as statistically relevant as it shows that wind forecasting is not 90% or 94% or 95% accurate.
Further more, under the “Information” button at the bottom right of the National Grid's Wind Forecast Out-turns graph: http://www.bmreports.com/bsp/bsp.php#wind_fc_outturnit it states:
“Wind Generation forecasts are produced by National Grid's own first generation windpower forecasting tool. The predictability of the wind varies with atmospheric conditions and so there may be periods where National Grid's forecast and outturn values differ significantly.”

djpbarry

Chloe Pink wrote: »

What would you rather I did, make stuff up?

No, but when you provide a source to support your argument, you cannot then detach your argument from said source in subsequent posts (“...I'm not claiming anything, I am pointing to information...”).

Chloe Pink wrote: »

Anyway, I do regard 3 days as statistically relevant as it shows that wind forecasting is not 90% or 94% or 95% accurate.

Does it? Based on what measure of statistical significance?

Capt'n Midnight

Chloe Pink wrote: »

I have written:
“I am pointing to information provided by experts in their field, in this case EON UK and they are quite explicit in what they say:

"On this basis, if the UK required, say, 40,000MW of wind capacity to meet its renewable target by 2020, only 8% of this renewable capacity (3,600MW) could be relied on to meet winter peak demand. This would avoid the need to build 3,600MW of new thermal plant but the remaining 36,400MW of renewable capacity would need to be "backed-up" by thermal plant to meet winter peak electricity demand in 2020."

why does it need to be backed up by NEW thermal ???
there are quite a number of oil power stations mothballed in the UK these could be prepared to go live at a few days notice , Inverkip power station - 1900 MW , there are others

Why does it need to the be THERMAL
Dinorwig has 1,800 MW of pumped storage , others could be retro fitted to Scottish dams
A Severn Barrier could produce up to 8,640 MW, with others on the English coast.
Existing link to France is 2,000MW

Biomass is still small in the UK - yes it's thermal but it's renewable and you can retrofit some existing stations to take it

The UK could also link to Norway for hydro

In the UK the big threat to supply is if someone cuts off the gas that provides a huge chunk of generation

Chloe Pink

djpbarry wrote: »

No, but when you provide a source to support your argument, you cannot then detach your argument from said source in subsequent posts (“...I'm not claiming anything, I am pointing to information...”).

http://oxforddictionaries.com/definition/claim

Claim
“1 [reporting verb] state or assert that something is the case, typically without providing evidence or proof”

djpbarry wrote: »

Does it? Based on what measure of statistical significance?

None. Basically any one occurrence of the daily forecast not being ‘∼94-95% accurate’ contradicts the statement that: “Same day forecasts are ∼94-95% accurate.”

My comment originates from Post 9 which states:
“Wind generation can be forecast up to one day in advance with over 90% accuracy. Same day forecasts are ∼94-95% accurate.”

The first sentence of the post, does not say that the forecasts “are” 'over 90% accurate up to one day in advance'; it says they “can” be and as such this first sentence means very little as it does not say for example, how often they “are” 'over 90% accurate up to one day in advance'.

However, the second sentence is presented as a statement of fact; “Same day forecasts are ∼94-95% accurate.”
There is no qualifying statement with this post (e.g. x percentage of the time / on average over a year / using statistical measure x) so I took it on face value as it was presented.
Yet when I looked at the link provided and at the link I provided to the National Grid, I observe that they are not ∼94-95% accurate.

In response to other posters questioning Post 9,
you say in post 11, “Eirgrid's wind generation forecasts match actual wind generation reasonably well.”;
and in post 13, “A cursory glance back over a few days’ data suggests the forecasts are at least 75% accurate on average.”

Despite other posters questioning of post 9 and despite the author’s variation from Post 9 (in Posts 11 and 13), Lenny Lovett (in post 44) quotes: “Wind generation can be forecast up to one day in advance with over 90% accuracy. Same day forecasts are ∼94-95% accurate.”
Regardless of what Lenny Lovett was trying to convey in relation to this quote, I felt it worth while to point out that the forecasts do not appear to run in accordance with this quote rather than let the quote be revived again as fact.
This approach seemed preferable to trawling back through what other people had said and also preferable as it would allow the reader to observe it for themselves.

As I said previously, any one occurrence of the daily forecast not being ‘∼94-95% accurate’ contradicts the statement that: “Same day forecasts are ∼94-95% accurate.”

More to the point though, even if we had accurate same day forecasts; we'd still need back up generators for our wind generators for the days when the wind simply isn't blowing much.

djpbarry

Chloe Pink wrote: »

Basically any one occurrence of the daily forecast not being ‘∼94-95% accurate’ contradicts the statement that: “Same day forecasts are ∼94-95% accurate.”

No, it doesn’t. I used ‘∼’ as short-hand for ‘approximately’. I was certainly not stating that every single same day forecast is 94-95% accurate (and I’m sure you knew that). The figures are from this presentation (slide 10), given by representatives of Eirgrid and SONI, which shows normalised errors for forecasts in 2007. ‘Same-day’ errors are approximately 5% on average, ‘next day’ errors are ≤ 10%.

Chloe Pink

djpbarry wrote: »

No, it doesn’t. I used ‘∼’ as short-hand for ‘approximately’. I was certainly not stating that every single same day forecast is 94-95% accurate (and I’m sure you knew that). The figures are from this presentation (slide 10), given by representatives of Eirgrid and SONI, which shows normalised errors for forecasts in 2007. ‘Same-day’ errors are approximately 5% on average, ‘next day’ errors are ≤ 10%.

You stated that ‘Same day forecasts are approximately 94-95% accurate.’
This reads that ’Each same day forecast is approximately 94-95% accurate’
Thank you for clarifying that this is not what you meant.

I guess a more accurate statement would have been along the lines that ‘x% of same day forecasts are approximately 94-95% accurate.’
This would take into the account the statement:

“• However, some forecasts have huge errors.”

as made on slide 10 of the presentation you link to: http://www.eirgrid.com/media/(4)%20Wind%20Forecasting%20Tools%20and%20Processes%20-%20Philip%20O'Donnell,%20EirGrid.pdf

To quote page 10 of this presentation:
"• Day ahead target accuracy is 6-8% on average.
• With-in day target accuracy is 4-6% on average.
• However, some forecasts have huge errors.
• Individual wind farm accuracy would be in the range 10-20%."

Anyway, as I said in my previous post, forecasting does not negate the need for back up generators for our wind generators as the wind blows when it wants to, where it wants to and how it wants to. The sometimes “huge errors” in forecasting are just another problem on top of a much bigger one.

djpbarry

Chloe Pink wrote: »

You stated that ‘Same day forecasts are approximately 94-95% accurate.’
This reads that ’Each same day forecast is approximately 94-95% accurate’

No, it doesn’t. I would have thought it obvious that “on average” was implied.

Chloe Pink wrote: »

I guess a more accurate statement would have been along the lines that ‘x% of same day forecasts are approximately 94-95% accurate.’

No, it wouldn’t. The slide in question shows the mean error for same-day forecasts is of the order of 5%. So, the mean accuracy of same-day forecasts is of the order of 95%. Considering individual forecasts in isolation is pretty pointless.

Chloe Pink wrote: »

Anyway, as I said in my previous post, forecasting does not negate the need for back up generators for our wind generators as the wind blows when it wants to, where it wants to and how it wants to.

But this is somewhat moot – who is arguing that we can get by with wind generation without the need for back-up supply?

Capt'n Midnight

The 94% figure for wind forecasting was at an error margin of +/- 20% of wind speed
Page 13 of this to see that 99% of the time they get the wind speed to within 30%,
http://www.eirgrid.com/media/(4)%20Wind%20Forecasting%20Tools%20and%20Processes%20-%20Philip%20O%27Donnell,%20EirGrid.pdf


looking at the power curve on page 4 http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CBIQFjAA&url=http%3A%2F%2Fwww.eirgrid.com%2Fmedia%2F(4)%2520Wind%2520Forecasting%2520Tools%2520and%2520Processes%2520-%2520Philip%2520O%2527Donnell%2C%2520EirGrid.pdf&rct=j&q=eirgrid%20wind%20accuracy%20&ei=V_HdTJqPCIazhAed65D7DA&usg=AFQjCNFl_U1aTeOp5HZ4b3qRtY4tbsLlKA&sig2=yHfbB5WOOJ9mEpZRQXE_vQ&cad=rja

for the region between 6m/s and 13m/s there is at most a 25% change of power for a 20% change in wind.

On the 6% of days they were more than 20% inaccurate this would mean a change greater than 25% in predicted output only if the wind was between 6m/s and 13m/s,

I don't have the data to determiine how often the wind speed on the inaccurate days was at the areas where changes in wind speed would not have affected power output at all (below 4m/s or over 15m/s) but I do know that the figures are +/- so you could assume that they may have under forecast the wind by as much as they over predicted it.


In simple English - getting the forecast wrong 6% of the time doesn't mean 6% of the time there were unforeseen outages. They quote it as +/- so maybe half those days there is more wind then predicted - so no reduction in power.
Using wind rose data you might guess how often that 6% translated into a significant power change (ie power output was out by more than 25% of predicted capacity)

Chloe Pink

djpbarry wrote: »

No, it doesn’t. I would have thought it obvious that “on average” was implied.

Not half as obvious as if you’d stated “on average”

djpbarry wrote: »

No, it wouldn’t.
The slide in question shows the mean error for same-day forecasts is of the order of 5%. So, the mean accuracy of same-day forecasts is of the order of 95%.

djpbarry: “No, it wouldn’t”
OK, fair enough, I am just trying to get to the bottom of exactly what you are saying.

djpbarry:“The slide in question shows the mean error for same-day forecasts is of the order of 5%.”
Doesn’t that depend upon the target that’s been set?
The bullet point on the slide in question refers to target accuracy”, not “forecast accuracy”.:
“With-in day target accuracy is 4-6% on average."
What is the target; for example the target might be that forecasting is within 20% of the actual turnout?

The fourth bullet point on the slide in question states:
“ Individual wind farm accuracy would be in the range 10-20%."
It is difficult to see how, if this is the case, “the mean accuracy of same-day forecasts is of the order of 95%.”

djpbarry wrote: »

Considering individual forecasts in isolation is pretty pointless.

It isn’t when you’re trying to match electricity demand and supply.
And this might explain why one of the four bullet points on the slide in question refers to individual forecasts: “However, some forecasts have huge errors.”

djpbarry wrote: »

But this is somewhat moot – who is arguing that we can get by with wind generation without the need for back-up supply?

I dispute that it's moot but am glad there's agreement on the need for backup.

djpbarry

Chloe Pink wrote: »

“With-in day target accuracy is 4-6% on average."
What is the target; for example the target might be that forecasting is within 20% of the actual turnout?

That would make absolutely no sense. I think it’s reasonable to assume that “target” refers to “forecast”.

Chloe Pink wrote: »

The fourth bullet point on the slide in question states:
“ Individual wind farm accuracy would be in the range 10-20%."
It is difficult to see how, if this is the case, “the mean accuracy of same-day forecasts is of the order of 95%.”

It’s not difficult to see at all – it’s plainly visible in the graph on the same page.

Chloe Pink

djpbarry wrote: »

That would make absolutely no sense. I think it’s reasonable to assume that “target” refers to “forecast”.
It’s not difficult to see at all – it’s plainly visible in the graph on the same page.

Try reading Capt'n Midnight's post no.54.
He says the '94% figure for wind forecasting was at an error margin of +/- 20% of wind speed'
And that '99% of the time they get the wind speed to within 30%'; not quite the same as "Same day forecasts are approximately 94-95% accurate".

Thank you by the way Capt'n Midnight and I will try and respond to your posts in response to mine when I get time. (I couldn't find a page 13 though).

djpbarry

Chloe Pink wrote: »

Try reading Capt'n Midnight's post no.54.
He says the '94% figure for wind forecasting was at an error margin of +/- 20% of wind speed'

An estimated mean will obviously have an associated confidence interval - are you trying to be pedantic?

Chloe Pink

djpbarry wrote: »

An estimated mean will obviously have an associated confidence interval - are you trying to be pedantic?

In line with point 10 of the Forum Charter, I will not respond to your question “...- are you trying to be pedantic?” with comments such as 'Maybe but better pedantic than obfuscate'.

Instead I will recap on three of the statements we have on this thread regarding our ability to forecast how, when and where the wind will blow and will recap on the two links on this thread that show wind forecasting versus turn-out.
This way, folks can look at the links every now and again and observe for themselves as to which statement best describes what they see overall.

Three statements:
Post 9 djpbarry “Same day forecasts are ∼94-95% accurate.”
Post 13 djpbarry “…forecasts are at least 75% accurate on average.”
Post 54 Capt’n Midnight “…99% of the time they get the wind speed to within 30%”

Two links:
http://www.eirgrid.com/operations/systemperformancedata/windgeneration/
http://www.bmreports.com/bsp/bsp.php#wind_fc_outturnit - (Click on the 'Wind Forecast Out-turn' tab for this one.)

djpbarry

Chloe Pink wrote: »

This way, folks can look at the links every now and again and observe for themselves as to which statement best describes what they see overall.

Three statements:
Post 9 djpbarry “Same day forecasts are ∼94-95% accurate.”
Post 13 djpbarry “…forecasts are at least 75% accurate on average.”
Post 54 Capt’n Midnight “…99% of the time they get the wind speed to within 30%”

Perhaps you could help "folks" by explaining how any 2 of those 3 statements contradict each other?

Chloe Pink

djpbarry wrote: »

Perhaps you could help "folks" by explaining how any 2 of those 3 statements contradict each other?

No I couldn't as they don't; this, as I'm sure you realise, is not the point in question.