Q2 2022: How heat waves will change the power system

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Dr Iain Staffell, Professor Richard Green, Professor Tim Green and Dr Malte Jansen – Imperial College London 

Never before has the UK experienced a 40-degree summer’s day – temperatures normally reserved for holiday destinations like the south of Spain.  On July the 19th Lincolnshire reached 40.3°C, breaking the national record by over 1.5 degrees.  This was a big test for the country’s infrastructure: railways buckled, airport runways melted, but the power system remained largely unscathed. 

Heat waves are increasingly causing major problems for power systems around the world.  Many of France’s nuclear reactors had to shut off because the rivers were too hot to cool them.  Meanwhile, low water levels in Germany’s rivers threatened shortages of coal deliveries to power stations.

Closer to home, the heat wave left the UK ‘very close’ to a shortfall in electricity supply.  This was not caused by plant outages, but rather the hot weather simply made power stations and transmission wires less effective.  Thermal power stations need to cool steam back to water as part of their thermodynamic cycle (hence the iconic cooling towers seen at many power stations).  This is harder to do when it is hotter outside.  At 40°C (a typical summer temperature in Saudi Arabia), a gas-fired power station can expect its capacity to be reduced by 13%, and its efficiency by 7% compared to when running at 20°C (the UK’s typical summer temperature).[1]  Now that the UK has experienced Saudi temperatures, its power station output was similarly degraded. It is not only supply, but also demand that has been impacted.  Across the US, Texas, California and Illinois had to ask citizens to turn down their air conditioning to prevent blackouts.  Japan had to scale back industrial production and limit air conditioner use, and parts of China have suffered the worst heat wave ever recorded, with several provinces completely halting industrial production for several weeks to keep the lights on.

Maximum daily temperatures in central England through 2022, set against the range of temperatures seen from 1922–2021.  Red areas indicate days that were warmer than average, blue areas show those that were colder than average.

Britain also saw increased electricity demand during the heat wave due to air conditioning and refrigeration loads.  The effect was muted though, with demand on the 19th only 6% higher than the same day the week before and after.  Even so, there was a 70% expected chance of demand outstripping supply on July the 18th, as this increase came at a time when demand would normally be low, and so power stations were offline for routine maintenance.  Electricity prices surged to nearly £750/MWh the following day (high, even by current standards), in much the same way as they do during the coldest winter spells.

Currently only 1 in 20 UK homes have air conditioning. This will undoubtedly increase as people struggle with the increasingly hot weather, and sales of air conditioning systems soared in the weeks around the heat wave.  As part of the efforts to decarbonise heating, it is expected that millions of households will install heat pumps over the coming years.  Air-to-air heat pumps can also operate as air conditioning units, and National Grid’s modelling expects these to take off rapidly in the coming decade.  Ten years from now there could be between 7 and 25 times more units installed than at present, meaning the demand surges we see in future summers could be much more difficult to accommodate.

Going forwards, Britain should not only expect more frequent and more intense heatwaves, but also that these will have a stronger effect on electricity demand due to changing consumer preferences.

Number of UK homes with heat pump air conditioners. 
Range of projections from National Grid’s Future Energy Scenarios

[1] Ambient temperature derating data from Wärtsilä and ADG Efficiency.

Live Grid Data