What happens when millions of Brits stop at once to watch the eclipse?

In some parts of the British Isles, astronomers predict the moon will obscure up to 95% of the sun. It will be a remarkable sight, and one that many of us may never see again, as the next is in 2090.

The historic nature of tonight’s solar eclipse doesn’t end there. It will change human behaviour too – and how we at the National Energy System Operator (NESO) keep the country powered.

Back in August 1999, for just 15 minutes, electricity demand plummeted by nearly 2.3 gigawatts – roughly equivalent to the power consumed by the cities of Birmingham and Manchester combined.

It then shot back up by a massive 3GW in a matter of minutes, representing the largest rapid increase in demand the British electricity network had ever recorded.

Although not quite so dramatic, we are preparing for this kind of change in demand tonight – one not seen since Covid - when we all broke with routine to stand on our doorsteps to clap for NHS workers.

As the moon begins to move across the sun from 18:08, the eclipse will dim daylight across the nation for almost two hours.

Millions will drop their usual routines to go outside to witness the spectacle - bringing with it a fall in electricity consumption. This is exactly the time we normally have the evening peak on the electricity grid, as we start cooking our evening meals, running the washing machine and watching TV.

But not tonight. The solar eclipse is expected to change everything, as millions gaze into the sky for the celestial event of the 21st century so far.

During the last total eclipse, Britain was overwhelmingly powered by fossil fuels, with solar power on the British grid measuring just a few megawatts.

Today, Britain is home to many large and small solar farms, with the sun capable of generating a significant 22.3 GW of our electricity. Solar power officially met a record 14.4% of our monthly need in July.

While tonight’s early evening eclipse will slightly affect the amount of solar power generated, it is a drop in the ocean for a system with a deep, diverse generation mix – that provides a lot of flexibility.

NESO is ready for tonight’s challenge, with our analysts and expert forecasters planning for many months - modelling the effect of shadow and light level on electricity demand.

We’ve been working with academics in solar modelling, as well as counterparts at the Met Office, who provide up-to-the-minute forecasts.

Indeed, our experts track and prepare for every conceivable scenario that might affect the network, months and even years ahead, to ensure supply and demand on our electricity network remains balanced, second by second, hour by hour, every day.

That’s why Britain has what is widely acknowledged around the world as one of the most reliable electricity systems on the planet, with a system reliability of 99.999%.

While you leave your usual routine and enjoy this celestial spectacle with friends and family, our engineers and control room teams will be focused on keeping electricity flowing.

As you head outside to watch tonight's eclipse, enjoy it. The moon may be travelling across the sun in the most dramatic style this millennium, but Britain’s power network won’t even blink and we'll be making sure the lights stay on when you come back in.

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Dr Deborah Petterson is the Director of Whole Energy System Resilience at the National Energy System Operator (NESO).

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