This is the fourth in a series of posts that look at UK Wind Power, in particular at its ability to contribute to peak demand, which occurs in the early evening, reaching its highest values during winter cold spells. Of particular interest is the wind power produced on the coldest evenings.
Data at 5-minute intervals for demand and metered wind power were downloaded from the gridwatch website ( http://www.gridwatch.templar.co.uk/download.php ) and plotted so as to reveal its essential characteristics.
The figure below shows the daily peak demand (in red) and metered wind power (in blue) at the times of the daily peak demand, for winter 2014/15:
The red demand curve in the figure above shows periodic dips at weekends, more substantial dips on Christmas and New Years days, and moderate peak demands during cold spells in January and February. The blue curve shows the intermittency of UK wind power, its small size relative to winter peak demand in 2014/15, and the fact that it almost vanished at several times of peak demand.
To show more clearly the contribution of wind power on the days of highest peak demand the data are shown again in the figure below, with an arbitrary offset of 54 GW added to the wind power. The 54 GW offset is indicative of how much dispatchable power was necessary to meet peak demand at that time. Also shown below is a graph of the Central England (HadCET) minimum temperatures when they are negative, together with the wind power.
The negative CET temperatures indicate the days of POTENTIAL high demand, some of which did not materialise because they fell during public holidays or weekends. The 3 cold spells are labelled “A”, “B” and “C” and are described below with UK Met Office summaries and synoptic charts.
“A” (28/29th December): “After a widespread frost on the morning of the 28th, it was dry, sunny and cold. The 29th again started with a frost, temperatures falling to -7.6 ºC at Benson (Oxfordshire); it was a dry, sunny but cold day. Early on the 30th temperatures again fell to -7 ºC in the Thames Valley area, but a dry and sunny day followed.” The light winds are confirmed by the following synoptic chart for 28th December 2014:
“B” (19th-24th January): “The 19th saw another cold start, but it was a pleasant day with scattered wintry showers in the north-east. Many areas were frosty again on the 20th, with -7 °C widely recorded in the south, but rain edged into the south-west during the morning. There was rain for many southern areas on the 21st and snow for many central and northern areas with Buxton (Derbyshire) recording a depth of 15 cm. High pressure began to build, and after another cold start in many areas the 22nd was mainly dry and sunny. A widespread frost on the 23rd saw temperatures as low as -8.8 °C in Upper Lambourn (Berkshire), but a fine day followed with only a few scattered showers in the west. Temperatures fell to -6 °C in parts of the south early on the 24th but again a fine day followed, albeit feeling cool in a north-west wind.” The early part of this cold spell had light winds, confirmed by the following synoptic chart for 21st January 2015:
“C” (2nd-4th February): “The 1st was a bright but cold day, seeing scattered snow showers in eastern areas, with Buxton (Derbyshire) recording a snow depth of 15 cm. There was a widespread frost on the 2nd with temperatures falling to -8 °C in Cumbria, but a bright day followed, with scattered snow showers in eastern areas. It began cold again on the 3rd, with -10.9 °C recorded at Bewcastle (Cumbria) but was another mainly fine day with only scattered snow showers for eastern coasts. The 4th started with a widespread frost, but a fine day followed with once again the east coast seeing scattered snow showers.” Light northerly winds are confirmed during this cold spell from the following synoptic chart for 4th February 2015:
The UK winter of 2014/15 was fairly average in terms of temperature, with 3 moderately cold spells, each of which involved light winds on some days. The graph of CET minimum (negative) temperatures, together with wind power, shows that mild spells were relatively windy, and cold spells (with potential high electricity demands) had relatively light winds.