Mapped: the £150bn megaproject that aims to protect Britain from energy shocks

Britain is embarking on one of the largest overhauls of its electricity grid in generations – a megaproject in which five times more infrastructure will be built by 2030 than was constructed during the previous three decades.

Tens of billions of pounds are being spent on new pylons, subsea cables and converter stations to connect a growing fleet of wind and solar farms and carry clean power to where it is needed.

It comes after successive global shocks – Russia’s invasion of Ukraine, then the Iran war – have exposed the vulnerability of the UK’s energy system to international market volatility and galvanised plans to bolster domestic low-carbon generation.

The cost of electricity in the UK has surged in recent years, far beyond that of comparable countries, largely because expensive gas-fired generation sets the price most of the time.

This volatility has accelerated efforts to transition away from fossil fuels, in the hope homegrown renewables can shield UK households from future shocks.

Yet that green drive is now being limited by Britain’s ageing grid, which, after decades of underinvestment, is often unable to transmit the new energy being generated.

“If we don’t have enough transmission network capacity, we won’t be able to make full use of renewable energy resources. We will then be more dependent on fossil fuels, with greater vulnerability to fossil fuel price shocks and higher CO2 emissions,” said Keith Bell, professor of electronic and electrical engineering at the University of Strathclyde.

Unblocking these bottlenecks will require well over 4,000 miles of new power lines by 2041, alongside significant improvements to cables already in place, Guardian analysis of official recommendations shows.

Much of that expansion will be visible, cutting across the countryside and bringing construction to rural communities along the way. It has prompted protests, with some residents claiming they face an “energy invasion” owing to the scale of the planned infrastructure.

Household energy bills are to rise in the short term to pay for the grid transformation, at a time when politicians are pledging cost-of-living support.

Britain’s National Energy System Operator (Neso) recently estimated that £64bn of investment will be needed for transmission projects by 2030 and a further £89bn beyond that – more than £150bn, which will be largely paid for by surcharges on household bills.

While these investments will eventually help lower costs by reducing reliance on expensive gas generation, on Friday the National Audit Office warned the government that dozens of grid projects risked delay, potentially placing further strain on consumers.

But a failure to build also has costs – as the below visual explainer sets out.

Grid upgrades will be largely paid for through household energy bills, coming on top of electricity prices that have risen sharply after global energy shocks.

The energy regulator Ofgem has announced that the energy bill price cap will rise by 4% from October to its highest level in three years, driven by increases in wholesale gas prices.

On the day of the price cap announcement, the energy secretary, Miatta Fahnbulleh, was challenged about whether “the drive towards net zero” was also costing people more. She replied: “Absolutely not.”

But Fahnbulleh went on to acknowledge that paying for upgrades would be unavoidable, saying: “For a decade and a half, under the last government, we didn’t invest in our energy system, we didn’t invest in the grid, and we’re going to have to deal with that. So for the grid to operate properly, we’ve got to upgrade it.”

Andy Burnham has attempted to reduce energy bills since entering Downing Street, with his first big policy announcement being a cut to VAT on them from 5% to 0%.

In the absence of further government intervention, rising network costs will soon add an extra £130 to a typical household’s energy bills by 2030, according to one forecast.

Ofgem has pointed out that households would still be paying more by 2030 if grid upgrades were not undertaken, due to the cost of curtailing renewables.

“While upgrades will require investment, failing to invest would also increase costs for consumers through higher constraint and balancing payments caused by grid bottlenecks,” a spokesperson said.

Many experts also agree that spending more on grid upgrades now alongside growing the UK’s low-carbon power capacity will lead to lower energy costs in the future.

Neso forecasts that full decarbonisation that meets the UK’s net zero targets could lead to energy spending falling from more than 10% of gross domestic product to less than 5% by 2050, owing to the wider use of cheaper renewables and lower waste.

Spending falls further than in a scenario with far less decarbonisation, in which the UK falls short its legally binding 2050 target, though it is initially higher because of the investment needed to increase renewable capacity.

Some argue there are ways to reduce the sharpness of this investment “hump” through a different approach to grid upgrades.

The Conservatives recently claimed transmission costs could be reduced by focusing on a smaller number of large nuclear and gas plants over many renewable sites, in turn reducing the number of new cables.

Others dispute those findings, pointing out that emissions would be higher – building nuclear sites requires large upfront costs and has proven to be difficult in recent years – and that gas prices are likely to exceed the assumptions used in their analysis.

Neso forecasts full decarbonisation would have a sizable benefit: shielding against energy shocks.

It has modelled the hypothetical impact of a 2022-style energy shock after Russia’s invasion of Ukraine on a fully decarbonised energy system in the UK.

The original shock cost an extra 1.8% of GDP – equivalent to tens of billions of pounds. In a full net zero transition scenario it would have been closer to an extra 0.3%, more than six times smaller.

“Our analysis suggests that delivering net zero by 2050 could halve energy-related spending, whilst also providing greater protection from global price spikes in the process,” a Neso spokesperson said.

However, experts say getting to that point will require more than just new cabling projects.

“Transmission is only one piece of the puzzle, though – greater storage, demand flexibility, and potentially green hydrogen production would all help drive down curtailment costs and cut dependence on expensive gas,” said Collett-White.

“A better, not just bigger, grid should be the goal.”

With the geopolitical landscape looking increasingly turbulent, ministers may be convinced that making households pay for a better grid – and the protection it affords – will be worth it in the end.

A spokesperson for the Department for Energy Security and Net Zero said: “Decades of underinvestment in the grid has left us overexposed to fossil fuel markets and unable to realise the full potential of clean, homegrown energy to lower bills for households.

“That’s why we’re building a decarbonised energy system that can bring down bills for good.”

A spokesperson for National Grid said: “Investment in upgrading the grid is supporting jobs, skills, and supply chains across Britain, while creating opportunities and benefits for local communities.

“We work closely with local people, consult extensively, and consider all technology options as we develop proposals for the infrastructure needed to support a secure energy future.”