UK wholesale electricity prices for the day ahead shot up as a heatwave in some parts of the country helped push up the demand for power.
The price has jumped from around 40 per megawatt hour to almost 200, the most expensive in a decade.
Demand from cranked-up air-conditioning comes on top of a lull in wind power and gas and nuclear power stations going offline.
Gas power stations provide over half the UK’s electricity.
The day-ahead price of electricity, the amount generators charge to put power into the UK network the next day, has rocketed in the past two days.
Power stations put electricity into the National Grid’s network and it is sold on to household energy suppliers.
Around a tenth of UK electricity is bought by suppliers at the day-ahead price. Wholesale electricity costs make up just under half of household electricity bills.
The heatwave hitting the south of England means air conditioning units are being turned up.
Demand is higher than average for September and at its highest since April, when a cold snap and snow storms led to severe weather warnings in parts of the UK.
The unseasonal September weather has also reduced wind power in the system.
And adding to the pressure, the number of gas power stations that have been shut down for planned maintenance is at its highest level since 2009.
Unplanned outages at other stations have compounded the problem.
Glenn Rickson, head of power analysis at Platts, said: “It seems to be the straw that broke the camel’s back this week.”
The surprise rise in demand and a drop in supply has left the UK with less spare power than usual. It comes after concerns about spare capacity going into winter.
Usually extra electricity can be drawn in from a connection between the UK’s grid and the French network, but the crucial cable is not working properly, limiting transfers.
In France, several nuclear power stations are also offline, meaning there is less electricity for the French to sell to the UK.
Nick Grogan, an energy industry analyst, said it was “almost the perfect storm”.
He added: “The price tells you suppliers are looking at the market and saying: ‘Is there enough power there?’
“It’s rare for it to get this bad.”
Keeping the lights on
National Grid admitted the UK’s electricity supply was “a little tight” but said it was “completely manageable”.
The operator said it was comfortable it had enough power in reserve to keep the lights on.
Factories have not been asked to reduce demands on the grid and emergency generating capacity has not been called on.
In a statement it said: “Electricity demand is picking up as we head into autumn, and some power stations are still offline for their summer maintenance programme, which is not unusual at this time of year.
“We are monitoring the situation and have tools and services we can call on if we need them.”
Read more: www.bbc.co.uk