The message
from David Hansen contains these words:

I don't think you can point me at any published
figures (you certainly haven't tried) that indicate that any of the
established wind farms can claim as much as 35%

I have come across capacity factors for wind farms up to ISTR 49%,
over a period of several years. However, that was on an island
exposed to more wind than even Northern Ireland (where the highest
capacity factors in the UK are recorded) and is not indicative of
what will be achieved elsewhere. However, Scottish Power quote
capacity factors of 35%-40% for their modern wind farms.

Do they? Seem not to on their website. And what google comes up with is
a very mixed bag. As I have said before it seems the dominant element in
load factor is wind (or lack of it). The Western Isles are a
particularly favoured location although it seems Shetland is even better
and perhaps a wind farm on Rockall or closer to home on St Kilda would
be better still. Shame it isn't an economic proposition to ship in
energy from the far flung locations.

The average capacity factor for UK onshore wind farms actually fell for
a period after 1998 and still hadn't struggled back to 1998 levels in
2004. That is partly due to the decline in mean wind speed over the
period but must also be partly do to the continued building of wind
farms in unfavourable locations.

"Conclusions
The regional onshore wind capacity factors in the UK between 1998 and
2004 ranged from 19 per cent in one of the least windy regions in a year
when the wind speed index was low, to 40 per cent in one of the most
windy regions in a year when the wind speed index was high, with the
overall UK average being 29 per cent. The quality of the data varies
over this period but with ROCs data available from 2003 the quality and
consistency of the data improved from this point. Using figures from
both NFFO and ROCs data streams increases the data coverage/capture and
means this analysis encompasses all wind farms in the UK.
The correlation between average UK wind speed and capacity factor in any
given year is good with an R2 value of 0.91."

But don't forget:

"Only aggregated figures can be released publicly under the
confidentiality requirements of ‘National Statistics’. Therefore, where
there were only 1 or 2 wind farms in operation within a particular
region, data for these regions were excluded; eg the South East is not
reported. These regional capacity factors were calculated using the
total capacity and generation within each region."

It reports other work. Nothing wrong with that. However, the flaws
in the RAE work were exposed years ago and I wouldn't put much
confidence in it. [snip]

But you haven't quoted your source

One of them is the UKERC report, section 3.3.2. That concentrates on
the RAE's assumption that dedicated backup would be needed for wind,
which is mince.

More smoke and mirrors.

Load factor is a different issue to the amount of backup required for a
variable source.

I recall another one where the authors said they had interviewed the
authors of the RAE report and they had been somewhat confused about
the different types of backup and were unable to give a convincing
answer about several aspects of their report. It was expressed in
academic language but was very cutting about the RAE's report.

and I don't take anything on trust from you.

Excellent, more personal abuse.

One only has to look at the point above that I have just responded to to
see why I don't trust you.

You are clutching at straws. The passage quoted came as close to
rubbishing the 35% as you are ever likely to see in an academic report
where there is genuine uncertainty in the wind.

People can read the report themselves and consider the veracity of
your assertion.

They can read the section I quoted for that. No need to bogged down in
the waffle.

--
Roger Chapman