Just 164 projects are currently under construction, according to the Local Government Association (LGA), while a further 1,300 wind, solar, hydrogen, waste and other projects are stuck in the pipeline.

The LGA cited problems connecting the projects to the electricity grid as a key barrier to getting them off the ground - an issue increasingly complained of by the industry.

Some developers are told they will have to wait years or decades to join the grid, which connects the power source - like a solar farm - with the end user, which could be a hospital building or a householder turning on the kettle.

An LGA spokesperson told Sky News: "Connection to the grid is increasingly getting the attention it deserves.

"We can talk about all these cool projects like solar, wind, heat, and so on. But if you can't link them up so that people can actually use the power they're generating - that's a major problem."

The power system is gradually being shifted away from fossil fuels towards a variety of cleaner power forms - including things like biomass or reusing heat from sewage works - with the aim of decarbonising the energy network by 2035.

The number of clean power schemes winning planning permission from councils is rising rapidly, doubling almost every year since 2018.

But a fifth of generation capacity waiting to be hooked up to the grid will have to wait at least 10 years, while 40% will have to wait until at least 2030, the regulator Ofgem warned in May.

"The story is basically positive in that there has been a sharp increase in renewable energy projects coming forward, but the lack of grid connections risks scuppering it in a significant way," the LGA spokesperson said.

The grid wasn't designed for the number of projects that are now lining up for connection in comparison with the past - an issue facing many countries trying to ditch fossil fuel power for electricity and heat.

The grid is 'major concern' - are there any solutions?

Trade association Energy UK called the issue a "major concern".

"With the targets we have in place for expanding our own sources of cheap, clean, domestic power and a big increase in demand for electricity over the coming years and decades, we cannot afford such delays," a spokesperson told Sky News.

It urged the government to publish recommendations by the Electricity Networks Commissioner on how to cut development time for such projects. The government promised to do so imminently.

A Department for Energy Security and Net Zero spokesperson said: "Significant progress has already been made, with a 500% increase in the UK's renewable energy capacity since 2010 - now the second highest amount connected to the grid in Europe.

They added: "We will expand on this by working hand-in-hand with Ofgem and network operators to cut the time it takes to build new network infrastructure and connect new energy projects to the grid."

Delivering this requires reform to the planning process and ensuring "communities feel they are directly benefitting from cheaper, secure, low-carbon energy", they said.

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In June the National Grid promised to kick "zombie" projects progressing too slowly out of the grid queue to free up space for ready-to-go projects like solar.

Lawrence Slade, chief executive of the Energy Networks Association, which represents the UK's energy network operators, said industry is "taking significant steps to address the short-term issues", including by connecting projects which are connection-ready first and delivering a more flexible queue management process.

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"These are the first steps in what we believe needs to be ongoing, evolving reform, so that network companies can continue to deliver for a future energy system which looks very different to today's," he said.

"Longer-term investment combined with holistic planning reform is essential so that the networks can continue providing a solid foundation to our net zero future."

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