An interesting and informative post, thanks.

On Sat, 14 Sep 2013 09:14:22 +0100, The Other Mike
wrote:

It's not contradictory, the general trend was the load dropping off at 4GW per
hour or at a rate of around 50MW per minute, following a very similar load
profile to yesterday, possibly close to the same day last week, and not too far
away from the same date last year, with corrections for temperature, wind chill
etc. Within that general downward trend was a very temporary 221MW pickup,
lasting a maximum of 5 minutes.

To cope with the general downward trend conventional generation will have been
scheduled to reduce output accordingly, this could be achieved by say 8 x 500MW
coal fired units reducing output from 500MW to 0MW by various set times across
this one hour period.

This conventional generation that is reducing output is solely working to a set
target of MW output, not to control to a set frequency.

Other generation (coal, gas, nuke), that is paid to provide frequency response
will attempt to cover any move away from the range of 49.95 to 50.05 Hz by
increasing or decreasing output from the current level.

As the 1900-1930 programme ends the temporary load pickup is provided by pumped
storage, this is normally a dispatched response, i.e. X MW 'now' or Y MW in 1
minute.

From 1920 to 2030 at 5 minute intervals Pumped Storage output was as follows

1920 684
1925 582
1930 491
1935 817
1940 748
1945 413
1950 387
1955 304
2000 276
2005 276
2010 281
2015 283
2020 333
2025 285
2030 282


So a drop in pumped storage output from 1920 to 1930 of 193MW and then an
increase of 326MW by 1935

Against this background of increased pumped storage output there is still the
conventional generation ramping down at 50MW a minute to follow the general load
profile and to complicate matters still further during this one hour 10 minute
period there was a variation in wind turbine output of from a low of 1688 to a
max of 2076MW or 388MW.
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