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The proposed Hinkley Point C nuclear power station

Of all the thorny questions facing Theresa May in her review of the Hinkley Point nuclear power project, one dominates the rest: could Britain keep the lights on without it?

If Hinkley is indispensable, scrapping the proposed power station in Somerset would leave the UK facing an energy crisis. If not, the prime minister has more freedom to address her concerns over costs and the security implications of Chinese investment in the project.

As with everything about Hinkley, the answer is mired in complexity and open to dispute. A recent report by the Energy & Climate Intelligence Unit, a think-tank, claimed Britain could not only survive without Hinkley but save £1bn a year in the process. Others see such a benign assessment as complacent and reckless.

Hinkley’s advocates portray the project as a crucial step in replacing the UK’s dirty coal-fired power stations and its existing but ageing nuclear reactors. About 60 per cent of UK electricity-generating capacity in 2010 is forecast to have disappeared by 2030.

Cancelling Hinkley would require the UK to find alternative sources for the 3.2 gigawatts of power — about 7 per cent of national demand — expected from the plant. Options for achieving this would be constrained by the government’s carbon reduction targets, which rule out a revival of coal or a large-scale shift to gas.

Arguments for ditching Hinkley tend to rely heavily on the potential for offshore wind to become the backbone of UK generating capacity, taking advantage of the country’s location on the edge of the north Atlantic.

While the cost of nuclear reactors continues to rise as technology becomes more complex and safety standards more exacting, wind power is moving the other way. “The price of wind and solar is falling so rapidly that the economic arguments for them are becoming as strong as the environmental ones,” says Doug Parr, chief scientist at Greenpeace, the environmental group.

At a cost of £120 per megawatt hour, electricity from the latest UK offshore wind projects remains more expensive than the £92.50 promised to EDF, the French utility planning to build Hinkley with Chinese backing. But the cost of offshore wind fell 11 per cent between 2010 and 2014 and further reductions are expected as the industry matures.

The UK is projected to have 37.9GW of wind capacity by 2030 under current plans, 60 per cent offshore. The ECIU reckons just four additional large offshore projects would be enough to replace Hinkley.

Critics say the intermittency of wind means it can never fully fill the gap left by old coal and nuclear plants. Hinkley would operate at full power for 80-90 per cent of the time, compared with 25-50 per cent for wind farms, depending on turbine size and location. “A megawatt hour of electricity from one technology is not necessarily equal to a megawatt hour from another,” said John Feddersen, chief executive of Aurora Energy Research, an Oxford-based energy analytics company.

Green power advocates argue that output can be smoothed over by using gas when winds are light. The ECIU report said six to 10 gas-fired units would be needed for this purpose, costing a fraction of Hinkley’s £18bn to build. But Tony Ward, a utilities expert at EY, the consultancy, queried where the investment would come from. “Who is going to spend £600m building a gas-fired power station that is only used a few days a year?”

Back-up power could also come from interconnectors linking the UK power grid with those of France, the Netherlands and Ireland. Imported electricity accounted for almost 6 per cent of UK supplies last year and is forecast to reach 12 per cent by 2030 as more subsea cables are built.

However, interconnectors can only offset UK shortages if there is surplus electricity available elsewhere, which cannot be guaranteed. “Weather is highly correlated across western Europe,” said Mr Feddersen. “When it is windless, in the UK it tends to be windless in France.”

Another way to manage peaks and troughs in output is to reduce demand when supplies are tight. The ECIU report cited studies showing that demand equivalent to several times Hinkley’s capacity could be removed by measures to make consumption more flexible and efficient. Heavy industries could schedule non-essential work away from times of peak demand while heating and cooling equipment could be temporarily turned down in sectors from retailing to data centres.

“We are moving from guaranteed power to a new world of uncertain supply,” said Mr Ward. Others see this more positively as a shift from “always-on” capacity to more efficient “smart” grids matching supply and demand. Advances in electricity storage — allowing surplus wind and solar power to be saved up — could further reduce the need for “baseload” power of the kind to be generated by Hinkley.

“Future grids will be smart, decentralised [and] flexible,” said Paul Massara, chief executive of North Star Solar, a renewable power company.

Others say new technology would not arrive quickly enough to avert a UK energy shortage. Even if Hinkley’s 3.2GW of power could be found elsewhere, its cancellation would call into question a wider programme of new reactors due to deliver 14GW by 2035.

“Alternative technologies will have an important role to play,” said Mr Ward. “But we are still going to need stable, large-scale baseload capacity for decades to come.”