Unprecedented daily winter extremes for the UK energy sector

As the UK power system transitions towards a greater share of variable renewable energy resources, the system becomes more weather dependent. During winter, the most challenging conditions occur when low wind speeds are accompanied by cold temperatures, driving increased electricity demand and reduced wind power generation. To understand the risks posed by such days, the magnitude and likelihood of these events is assessed, using a large climate model ensemble combined with simple empirical relationships to quantify electricity demand net of wind power (DnW) from meteorological variables. It is demonstrated that the annual probability of experiencing a winter day with higher demand net wind than observed is approximately 1% (1 in 103 years) under the current climate. This represents a 10-fold decrease in probability since the 1960s and is primarily associated with a similar reduction in the probability of an unprecedented cold winter day (a 10-fold decrease to 1.3% each year under present climate). The probability of an unprecedented low-wind day is low (0.4% each year) and has remained largely unchanged over the same period. The large sample size also highlights the meteorological conditions driving these extreme high DnW days. It is found that all high DnW days are associated with low-wind conditions (i.e., very low wind generation is essential for high DnW to occur) but the severity of the DnW event is strongly influenced by the temperature (i.e., the level of demand dictates the magnitude of the DnW). Synoptically, this is associated with a reversal of the climatological pressure gradient over the North Atlantic. The most severe DnW days occur when high pressure is located over Greenland and extends to the UK, leading to a weak but cold northerly airflow over the UK.