The UK is set to spend its first full day without generating electricity from coal on Friday, the National Grid says.
It said it had run coal-free before, but the longest continuous period was 19 hours, first achieved last May.
It comes as less-polluting natural gas and renewables play a bigger role in supply - although the demand for power is also lower on Fridays.
The grid said it would only know for sure if it had achieved the feat by "22:51 on Friday".
Britain opened its first coal-fired power station in 1882 and coal remained a dominant part of the energy mix until the 1990s.
However, its use has fallen in recent years, as plants closed or switched to burning biomass, and it accounted for just 9% of electricity generation in 2016 - down from 23% the year before.
Last year, the government said it wanted to phase out Britain's last plants by 2025 as part of efforts to cut carbon emissions.Image copyright Getty Images Image caption The Clean Air Act was in introduced in 1956 to tackle the smog coal fired stations created by in big cities.
Analysis: Eyes On Events industry correspondent, John Moylan
Coal has powered Britain for more than a century. But today's landmark moment - the first 24 hour period without any coal powered generation - is a sign of how the once mighty fuel is being consigned to history.
Part of the reason is that solar panels and wind turbines now provide much more electricity to factories and homes. Lower power demand is a factor too - that's normal on a Friday.
And as older, uneconomic coal fired plants have closed in recent years, the fossil fuel has been playing a much smaller role in our energy system.
Paul Ekin, professor of resources and environment policy at University College London, said a full day day without coal would be "enormously significant".
"As recently as the late 1980s coal was supplying as much as 70% of UK electricity," he told the Eyes On Events.
"We then had the dash for gas in the 1990s, with nuclear roughly contributing around 25%, and coal dropped below 50%."
He said the current thrust was to replace coal with gas but that renewables like wind and solar were also playing a bigger role - accounting for 25% of supply in 2015.
Hannah Martin, head of energy at Greenpeace UK, said the first day without coal in Britain since the Industrial Revolution "would mark a watershed in the energy transition".
However, Cordi O'Hara of the National Grid said coal still had a role to play as the UK transitioned to a low carbon system.
"Our energy mix continues to change and National Grid adapts system operation to embrace these changes."Image copyright Getty Images Image caption The Ferrybridge coal-fired power station in West Yorkshire closed in 2016 after 50 years in service.
Key moments for coal-fired power
- 1882 - The world's first public coal-fired generating plant is opened at Holborn Viaduct in London
- 1956 - The Clean Air Act (1956) is introduced to tackle the smog created by coal fired stations. Coal-burning power stations are moved out of cities
- 1970s - Coal for heating homes is increasingly replaced by natural gas from the North Sea
- 1980s - Nuclear power grows to around 25% of electricity generation
- 1990s - 'Dash for gas' as natural gas grows to around 30% of electricity generation, largely substituting for coal
- 2015 - Renewables account for 25% of power supply
- 2016 - Government says it wants Britain's last coal power plants to close by 2025.