The message
from David Hansen contains these words:

Never trust politicians statistics.

I don't.

Are you suggesting that the University of Oxford
Environmental Change Institute are politicians?

They could be and in any event even scientists are not always as
impartial as circumstances should demand.

snip

"Capacity value of wind

"Due to the variability of wind power, its capacity value is more
limited, as it will not be possible to displace conventional
generation capacity on a ‘megawatt for megawatt’ basis. The capacity
value decreases as more wind is installed on the system; at low
penetrations it has been put at roughly equal to the capacity factor
for wind (30-35%), but at higher penetrations the value decreases.
This is because with low penetrations wind output is hardly noticed
on the system, but when this increases, the variability of wind
becomes more noticeable and its ability to provide firm capacity is
reduced. National Grid Company have stated that 8,000 MW of wind
capacity would displace 3,000 MW of conventional plant, with 25,000
MW displacing the need for 5,000 MW. This means that wind power has
a capacity value of around 35% at penetrations of around 6%,
declining to around 20% at penetrations of 20%. These figures, along
with other corroborating evidence, were accepted by the House of
Lords Science & Technology Select Committee in their 2004 report
into renewable energy.

It seems to me that this argument is based on the average output. No
wind at all might be almost impossible but what about the presumably
near 50% of the time when the output is below average? Sometimes it will
be well below average.

--
Roger Chapman