The case for decarbonising power supplies in order to limit climate change is now beyond challenge. The best way of doing it is as contentious as ever. Every option – carbon capture and storage to reduce coal-fired power stations’ emissions, expanding wind and solar power, developing other renewables such as tidal power, cutting consumption and bringing new nuclear capacity on stream – each has its own daunting problems, although some look a lot cheaper to fix than others. In China this morning the chancellor, in his role as prime-minister-in-waiting, dangled yet another carrot in front of nervous investors, promising a further £2bn of credit guarantees for investment in EDF’s new European pressurised reactor at Hinkley Point C in Somerset. Two-thirds of the estimated £24bn cost of building the power station is now covered by government guarantees, even though EDF has agreed a “strike” price – what it will be paid for its electricity – that will make it the most expensive in the world while earning the company, when fully on stream, an estimated annual profit of £5bn.

The need for a non-polluting, reliable source of energy has changed attitudes to nuclear power. It is now accepted, at least by some ex-critics, as the least bad option in a world where a fast-growing population and the multiplication of energy-hungry tech devices will hugely increase demand for the foreseeable future. That was why the last Labour government gave the go-ahead to third-generation nuclear power at Hinkley, and why neither the coalition nor this Conservative government imagine cancellation is an option. Yet it is looking more and more like a bum deal. Overpriced, overcomplicated and overdue, as the UK’s three most prominent green converts to nuclear energy, George Monbiot, Mark Lynas and Chris Goodall, argued last Friday when they wrote an open letter calling for the project to be abandoned and for nuclear generation to be concentrated on small modular reactors, cheaper, factory-made and – a bonus – highly suitable for export to developing countries.

Hinkley C is expensive because it is very big and very complex. For more than a decade, EDF, the state-owned French energy giant, has been building two similar reactors, one in France and one in Finland, both of which are running late and neither of which has generated so much as a watt of electricity. EDF won the Hinkley contract partly because of the Treasury obsession with not spending public money, but it is struggling to raise the private finance. That is one reason why George Osborne is buttering up the Chinese with potentially costly blandishments. For a while, there was resignation about the project’s cost. It was a price that had to be paid to keep the lights on and the tablets charging. But in the past few years, it has looked less and less like the next generation in clean energy and more and more like a rerun of the Sizewell B debacle, when the government of the day found itself locked into an outdated technology.

Meanwhile, renewables are rapidly proving more efficient than predicted – that’s the official explanation for withdrawing subsidies – and their costs are falling. They are still a long way from offering a real alternative to established nuclear power. But the danger is that the cost of making Hinkley C work will have a perverse effect, slowing the development of green alternatives. Germany has been here already. In 2011, Angela Merkel, in the wake of the Fukushima disaster reversed her planned extension of the life of nuclear capacity. Instead, it will be phased out entirely by 2022 (shortly before Hinkley C might finally come online). The move is not cheap, it has led to more reliance on coal, and individual renewable projects provoke strong local opposition. But it has also led to a doubling of energy efficiency. One windy day last July, 80% of Germany electricity came from renewables. As the ad says, Vorsprung durch Technik: forward through technology.