Seil Chat

Anyone measuring the wind speed? I just got back from the shop. The Bay is a sight.

mags
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There was a gust of 100mph recorded at Glen Ogle in Stirlingshire earlier - about the same time I drove through that area this afternoon in a high sided van van - it was an interesting trip, with a big detour round a fallen tree at Crieff.

Certainly the worst Summer storm I can remember.

Global Warming? I think so.

mags
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Maggie wrote:Global Warming? I think so.

mags
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Naughty Mags . . . we can't extrapolate from individual storms. However, there do seem to be more and more extreme weather events across the world.

Wouldn't have happened if we'd had more nuclear!!

And too windy for turbines!!

MonaLott wrote: And too windy for turbines!!

Much too windy for wind turbines, most of them would have automatically shut down for self preservation. Of course that is the ones that were still standing, I expect that there would have been a few mangled casualties yesterday.

brodie wrote:. . . of course that is the ones that were still standing, I expect that there would have been a few mangled casualties yesterday.

What evidence do you have for that Brodie? If you check the latest Google UK results for 'wind turbine damage' there are no reports. Much stronger winds/gusts than were experienced yesterday occur in Winter or out at sea. As for shutdowns - the Whitelee turbines were reportedly spinning yesterday evening . . . don't know if they were shut down for part of the day, but even if they were turbines in other parts of the UK will have been producing their full rated output in the strong winds.

The internet contains numerous instances of wind damaged turbines such as the one portrayed on the community website Easdale People :-

http://www.easdalepeople.org.uk/?p=356

There are other instances available on the internet, but most instances of wind damage are not publicised due to the embarassment to the owner, the maufacturer and the Wind Industry in general. However, a Summary of Wind Turbine Accident data to 31st March 2011 can be found on the Caithness Winfarm Information Forum :-

http://www.caithnesswindfarms.co.uk/page4.htm

A technical point - no wind turbine is 100% efficient and consequently no wind turbine produces it's rated power. It is not physically possible to extract sufficient power from the wind to be 100% efficient no matter how strong the wind. Betz Law states that the theoretical maximum power efficiency of any design of wind turbine is 0.59 or 59%. Typically, rural wind turbines in Scotland are 15 to 22% efficient, offshore wind turbines are much more efficient. For example, the 6Kw rated power wind turbine that was recently refused planning permission on Easdale island would only have produced an average power of approximately 1Kw.

Wind turbines use various techniques to prevent damage in strong winds, some utilise automatic shutdown, others use ‘furling’ in the form of ‘blade twist’ and ‘coning’ which will limit the power contribution of higher wind speeds. So strong winds such as those being experienced currently do not necessarily achieve better wind turbine performance apart from the obvious fact that a strong wind is better than no wind at all.

brodie wrote:A technical point - no wind turbine is 100% efficient and consequently no wind turbine produces it's rated power. It is not physically possible to extract sufficient power from the wind to be 100% efficient no matter how strong the wind. Betz Law states that the theoretical maximum power efficiency of any design of wind turbine is 0.59 or 59%. Typically, rural wind turbines in Scotland are 15 to 22% efficient, offshore wind turbines are much more efficient. For example, the 6Kw rated power wind turbine that was recently refused planning permission on Easdale island would only have produced an average power of approximately 1Kw.

There are a few misleading statements in Brodie's 'technical point'.

Nameplate capacity should not be confused with Power Coefficient (which is where Betz' Law comes in). The nameplate capacity of a wind turbine is the amount of power it will actually output in optimum conditions. So - if the Enercon turbines proposed for Clachan have a nameplate capacity of 900kw then they will output 900kw over the optimum wind speed range. (Not, as Brodie is suggesting, 59% of the nameplate capacity). From the figures in the diagram below it can be seen that the proposed Clachan turbines would begin to generate power at 3m/s or around 6mph and would put out their full nameplate capacity of 900kw (or more) in windspeeds between 16m/s and 25m/s (their cutoff speed). For the non-metric, this means wind speeds between 35mph and 56mph.

The figures in the right hand column show the Power Co-efficient, and as Brodie points out this cannot exceed 59%. In fact this particular model of turbine is operating at its maximum efficiency (50% in this case) in mid-range windspeeds of 8010m/s. At higher windspeeds a lower percentage of the energy in the air is being extracted, but there is a lot more energy, so the nameplate (or rated) capacity of the turbine is being achieved.

The capacity factor is the amount of energy produced over a period of time compared to the nameplate capacity. The average capacity factor for Scottish wind farms over the six year period 1998 - 2004 was 30%, and this is what is generally used in calculating wind power potential onshore in Scotland, not the 15%-22% Brodie quotes. Of course, this capacity factor will vary from location to location, and is likely to be slightly higher in Argyll. I believe Mr. Young is working on a capacity factor of 33%, or one third.

Are we confusing blade efficiency and generator efficiency?

Are turbine efficiencies 'rated' when driven by blades or some other power source?

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We are talking about the efficiency of the entire machine. The power co-efficient shown on the table above is the percentage of the energy in the wind passing through the rotor that is actually being extracted as electricity. As wind speeds increase this percentage drops because the power output of the turbine remains constant. The most efficient wind turbine you could ever build would never achieve a power co-efficient of more than 59%, but this does not have any bearing on a turbine's nameplate or nominal capacity.

(A wind turbine isn't a turbine driven by blades - the blades (plus the generator) ARE the turbine. A turbine is just a rotary engine that extracts energy from a fluid flow and converts it into useful work)

NickB, you are of course correct, I appologize for the lack of clarity in my previous post on this subject and for any confusion, I was in a bit of a hurry. As you correctly state a wind turbine will produce it's rated power when operating under rated wind speed conditions.

As far as capacity factor is concerned the range that I quoted applies to microgeneration equipment such as that proposed for Easdale Island. This is based on the Carbon Trust and the UK Met Office: “Small-Scale Wind Energy, Policy Insights and Practical Guidance” who state that “rural turbines have typical efficiencies of 15% to 20%”. As you state the wind in Argyll is likely to be higher on average which is why I quoted the range as 15% to 22% ( the turbine manufacturer quotes 11% to 22%).

Windfarm wind turbines are much larger than micro-generation equipment and are generally better located in terms of their hub heights and their all round exposure to the wind which indeed gives rise to higher capacity factors. You do not quote your source for 30% capacity factors and I am surprised that anyone is assuming 33% as this is more typical of an offshore location, however, I assume that a wind speed trial is being conducted in situ over a period of at least a year which will produce a highly reliable forecast for the likely capacity factor that would be experienced.

I do not claim to be a turbine expert as such and I have borrowed from the technical representations submitted by Mike Jones in response to the Easdale Island wind turbine planning applications.

Maggie, I am informed by Easdale Island residents that wind measuring equipment has now been erected on Easdale Island and it is likely that the winds of the recent storms have indeed been recorded.

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Brodie,

Completely agree - the proposed turbine on Easdale island would have a much lower capacity factor, probably in the order of the 15-20% you suggested.

Re. the wind resource at the Clachan site - a document available on the West coast Renewables website says:

Obviously, the capacity factor is dependent upon the available wind resource. The better the wind resource: the higher the capacity factor. Based on actual figures from similar sites in Argyll, Clachan Wind Farm is expected to have a capacity factor between 35 – 40% which is significantly above the national average.

I would take that with a pinch of salt - but it is a windy spot and I would expect the capacity factor of any machines installed there to be above the national average.

Capacity factor is highly location dependent, the fact that some wind turbines in Argyll achieve a particular capacity factor is no guarantee that any other wind turbines in Argyll will achieve the same.

For commercial Wind Farm installations it is normal and best practice to conduct a wind speed trial in situ over a period of at least a year which when used with the wind turbine power generation characteristic will produce a highly reliable forecast for the likely capacity factor that might be experienced in practice provided that other factors such as grid availability, wind turbine availability, maintenance and repairs etc. are also taken into account.

Due to the vagaries of the wind and the topographical effects at wind turbine locations it is not wise to assume a vaue for capacity factor; wind performance should be recorded in situ in order to measure and assess the viability of the wind resource.

brodie wrote: Due to the vagaries of the wind and the topographical effects at wind turbine locations it is not wise to assume a vaue for capacity factor; wind performance should be recorded in situ in order to measure and assess the viability of the wind resource.

I believe the intention is still to install monitoring equipment and monitor the wind resource at Clachan Farm for a period of at least a year before any turbines are erected. Apart from anythng else I would imagine the planners will need to be convinced that the wind resource is sufficient to merit the development going ahead.

Calibrating the wind resource would indeed be a wise course of action.

As far as the A&B planning department is concerned past experience with the planning application that was refused for a wind turbine on Easdale has shown that they did not challenge the absurd performance claims made by the applicant. The applicant claimed a likely performance above the range quoted by the wind turbine manufacturer without any substantiation and without performing any wind measurement.

The same was true for the exagerated performance claims made in the planning application for an Air Source Heat Pump and Solar PV panels on Easdale which was granted planning permission. The performance claims were not challenged by the planning department.

It is possible that the A&B planning department does not have sufficient technical expertise to make such challenges and that any claimed technical performance is accepted at face value.

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New montage from Whinbank by PACT:



Brodie, not sure if the final planning permission will be contingent on the wind resource being demonstrated to be as 'guesstimated' or not - might be worth objectors looking into that.

I agree that this would be a wise course of action. If the wind resource is unmeasured and unsubstantiated then any potential benefit from the project is not demonstrated practically, it would only be intuitive. The cubic relationship between wind speed and power generated is critical and any effective prediction of wind turbine performance has to be based on a wind speed trial.