So far, 2026 has been GB’s sunniest year on record. It won’t feel like it on the evening of 12 August when the Moon will cover 91% of the Sun over the country, removing 93% of its light. The eclipse begins at 18:07 BST, peaks at 19:12, and ends at 20:08. The last partial eclipse, on 29 March 2025, covered a third of the Sun, and reduced solar generation by a peak of 1.7GW.

NESO has included the upcoming eclipse in its latest transmission demand forecast. Their 12 August view carries an increase of about 1.1 GW during the eclipse. Whether that is enough to cover lost solar generation will depend on the weather. On a clear evening the eclipse could reduce embedded solar generation by an average 1.8 GW between 19:00 and 19:30.

Key takeaways

• On 12 August the Moon will remove 93% of the Sun's light over Britain at 19:12 BST, the deepest eclipse Britain's solar fleet has seen since 1999. On a clear evening that could take about 2.2 GW of solar off the system at its deepest point.
• Over the GB’s last partial eclipse in March 2025, NESO did not forecast a reduction in embedded solar generation. Gas and batteries ramped via BM offers to cover 73% of the generation gap.
• This eclipse is now in NESO’s week-ahead demand forecast, predicting just under 1.1 GW of embedded solar generation ramping down. That would cover the event on a partly cloudy evening. On a perfectly clear one it would not.

How much solar will the eclipse remove?

The upcoming eclipse will cover roughly three times more of the Sun than the last partial eclipse in March 2025. Despite that, the amount of solar generation lost from the system will be similar, as it is later in the day.

The March 2025 eclipse came late on a Saturday morning and slowed the solar ramp-up, with peak losses of about 1.7 GW. This one lands on a Wednesday evening, beginning over northern Scotland at 18:07 BST and ending in South West England at 20:08, just as solar is already falling away. It accelerates the solar ramp-down.