Britain’s power grid came under unexpected pressure this week on what should have been a fairly unremarkable day. There were no major, unexpected power-plant failures or extreme weather, and plenty of wind power was being generated in Scotland. But bottlenecks on the network meant not enough electricity could reach London and southeast England, forcing the grid operator to take emergency action on Monday to secure additional imports from France.

The episode exposed a longstanding shortcoming in Britain’s electricity system: The country can have enough power overall and still struggle to get it where it’s needed. The UK has built much of its growing supply of wind power far from where electricity demand is concentrated — and is adding wind farms faster than it can construct the infrastructure needed to carry that power south.

That mismatch is becoming increasingly expensive. In September, the UK paid a record of just over half a billion pounds to balance its power system, according to data compiled by LCP Delta. October could prove even more expensive, with actions taken on Tuesday alone costing £38.4 million ($51.2 million), a single-day record, the energy consultancy found.

“This is something we’ll keep seeing,” said Shivam Malhotra, head of power trading at LCP Delta. “We will see these records broken.”The mounting bill reflects what the National Energy System Operator pays to balance supply and demand and keep the network operating smoothly. A large part of that involves managing constraints: paying wind farms in Scotland to switch off because there isn’t enough transmission capacity to carry their power south, and then paying far more for gas plants closer to major cities to fire up instead.

“These wind farms were built with very limited consideration of where that electricity would be consumed,” said Jason Mann, senior managing director at FTI Consulting. “Those costs are locked in for generations.”This week offered a stark illustration of the problem. Britain had plenty of electricity. It just wasn’t in the right place. Transmission infrastructure in southeast England that had been expected to return to service remained unavailable, according to NESO, further limiting the amount of electricity that could be moved into the region. Even as NESO sought additional supplies from France, electricity continued flowing out of the south of England to Belgium, the Netherlands and France through other connections.

Ultimately, consumers pick up the tab. Windy and sunny conditions can push wholesale power prices lower, but those savings can be eroded when grid bottlenecks force NESO to pay gas plants elsewhere to switch on.

The UK’s Energy Secretary Miatta Fahnbulleh acknowledged the shortcomings of the current system at a parliamentary hearing this week, calling it “candidly not fit for purpose.”But she pushed back against concerns that the strains could threaten supplies, saying she was “100% confident the lights won’t go out this winter.”The resilience of the system has nevertheless come under scrutiny. Ofgem is investigating NESO’s handling of an incident during a period of extreme heat in June, when tight power margins put the grid under pressure.

No customers lost power, but the regulator is examining whether relevant security standards were met. What’s less clear is how quickly the underlying problems can be fixed.

Many of the grid’s current issues can be traced to a policy implemented in 2010 under then-Energy Secretary Ed Miliband known as “connect and manage,” according to FTI’s Mann. The policy allowed renewable power projects to connect before all the grid infrastructure needed to carry their electricity to consumers was in place.

Successive governments of both major political parties then subsidized a rapid expansion of wind generation without a comparable buildout of transmission infrastructure. The result is a growing gap between where electricity is generated and where it’s needed — and an increasingly costly job for NESO to bridge it.

The risk was identified even before the policy took effect. In 2008, John Mogg, then chairman of energy regulator Ofgem, wrote to Miliband warning that allowing more renewable generation to connect in Scotland before transmission capacity was expanded could cause constraint costs to “increase significantly.”Back then, Mogg cautioned that the cost of constraints had reached some £300 million. This year the figure could be 10 times that amount, based on data published by NESO and the grid operator’s forecasts.

Last year, in a second stint as Energy Secretary, Miliband rejected a switch to a zonal electricity market, which would have introduced different power prices across Britain to better reflect the physical limitations of the grid. Higher prices in the south, for example, could signal gas plants there to switch on and electricity to flow into Britain through interconnectors when needed, rather than leaving NESO to correct for those imbalances after the market has settled.

With that reform off the table, the UK is instead relying heavily on building more transmission capacity between the north and south.

“The long-term choice for the UK is between investing once in modern grid infrastructure or continuing to pay for imported fossil fuels year after year,” said Benj Sykes, UK chair of Danish offshore wind company Orsted A/S. The government and transmission operators need to accelerate grid upgrades, storage and other forms of flexibility, he said, both to improve energy security and “tackle the energy affordability challenge” facing consumers and businesses.