The United Kingdom could experience a power supply margin shortfall during the solar eclipse on Wednesday, as high demand from a new heatwave sweeping across Britain and the rest of Europe compounds the pressure on the electricity grid.

The National Energy System Operator (NESO) issued a notice today to encourage market actions that would increase system margins. While there is no risk to customer supplies, the alert was triggered because the eclipse will block sunlight between 6:00 p.m. and 8:00 p.m. local time on Wednesday evening, temporarily reducing solar power generation. The UK has around 16 gigawatts of installed solar capacity, meaning even a partial obscuration of sunlight can remove a meaningful slice of supply during a high-demand window.

For the period from 18:00 to 20:00 hrs on Wednesday, August 12, the system margin shortfall is estimated at approximately 1.2 gigawatts (GW), the operator said. The current contingency requirement stands at 676 megawatts (MW), while 1,000 MW of generation is excluded from the available system margin due to system constraints. NESO warned that Maximum Generation Service may be instructed.

An electricity margin notice serves as a signal to the electricity market, indicating that the energy system operator would like a greater safety cushion between power demand and available supply in the short term. Such a notice "does not signal that blackouts are imminent or that there is not enough generation to meet current demand," the operator emphasized. NESO, which became the UK's independent electricity system operator after separating from National Grid in 2024, uses such notices routinely as an operational tool rather than an emergency measure.

Energy system operators and electricity producers across Europe are similarly preparing for a temporary drop in solar power output during Wednesday's eclipse. The solar eclipse will be total and observable for parts of Greenland, Iceland, Spain, and Portugal, while most European countries will experience a partial solar eclipse. Continental Europe's solar capacity has grown substantially in recent years, with the EU adding a record 56 GW of installed solar in 2023 alone, making rapid ramp-down and ramp-up of solar generation during eclipses a notable balancing challenge for grid operators.

For Europe, this marks the first total solar eclipse in three decades. The UK will see a partial eclipse; at its peak, approximately 90% of the Sun will be covered by the Moon as viewed from London. In Cornwall, as much as 95% of the Sun could be obscured.

By Tsvetana Paraskova for Oilprice.com