The amount of capital earmarked for Hinkley C (£18bn) would produce more electricity over the next 25 years if it were invested in onshore wind or PV. Based on the projected economics for the first three lagoons, tidal power would be about 65% as productive but the projects would then last twice as long as nuclear.

If it operates at 85% of capacity, Hinkley C will produce about 24 terawatt hours of electricity a year, about 7% of the UK’s consumption. At today’s prices, PV on which the same amount was spent would generate 25 terawatt hours annually and onshore wind about 31. The Swansea lagoon and its proposed follow-on sites would produce about 15 terawatt hours.

The economic arguments for using renewables rather than nuclear are therefore increasingly strong.

There is very little uncertainty about the actual costs of wind and PV, or the direction of travel. Both are reducing in cost, with solar declining at about 6-9% per year around the world and wind somewhat more slowly. We do not know what will happen if Swansea and other lagoons are built but it is likely that we will also see substantial cost reductions there. Hinkley C is subject to much more uncertainty. The new nuclear sites in Normandy and Finland are proving hugely problematic and even the constructibility of the EPR is in doubt.

The annual running cost of Hinkley C, including its fuel, will be about £360m. This compares with estimates of £130m for £18bn of PV and £310m for onshore wind of the same cost. The lagoons will cost about £75m. All three alternatives to Hinkley will therefore be cheaper to operate, perhaps by over £200m a year.

£18bn worth of PV would take up about 0.2% of the UK’s land area. This is not an obstacle.

Nuclear power is proving difficult to fund and is subject to many concerns, both technical and financial. The only remaining argument for supporting Hinkley C is that therefore it will produce a constant flow of electricity 24 hours a day, if it is successfully completed.

In some circumstances this is an advantage but as wind and solar increase in importance this benefit will die away. There will be times when the UK would like Hinkley to produce less than its maximum output. Even this coming summer it is conceivable that on a sunny, windy weekend day that the UK will not need its full existing output from nuclear power stations and would prefer that they operated at less than 100% output. This is currently impossible. As the maximum output from PV and wind increases over the coming years, the inflexibility of nuclear will become an even more significant problem for the UK grid, particularly if electricity demand continues to fall.

A portfolio of tidal lagoons with storage capacity – something that can be engineered in - combined with PV and wind would represent a cheaper way of achieving a fully decarbonised electricity supply. Extensive use of ‘demand response’ and time-of-use tariffs could help shape demand to the expected availability of power.

In addition, battery storage is becoming cheaper by the month. Grid operators around the world are installing banks of containerised batteries to help maintain stability. The latest example in Korea has just seen the installation of a 50 megawatt system to replace older fossil fuel plants that used to provide power for hours of peak demand. This operator expects to save three times its cost over working lives of the batteries. In the UK, batteries can provide short-term storage overnight and could deal with unexpected swings in the availability of power.

An effective 21st century energy supply system will almost inevitably be based around renewables and batteries. The pace of cost reduction of PV makes this almost a foregone conclusion. It is already cheaper than nuclear per unit of capital invested. Automation and control of electricity consumption is making it easier every month to deal with the variability of wind and solar supply.

The only remaining problem is long-term storage. It must be provided by the conversion of surplus electricity in the summer, or in periods of gales, into methane for injection into the gas grid. The technology for turning power into hydrogen through electrolysis is simple and well understood. Several types of microbe can then take the hydrogen and a stream of impure CO2 and turn it into methane quickly and cheaply. The new Electrochaea pilot at a waste water pilot in Copenhagen will show how this can be done. The German company Microbenergy offers a similar route to so-called 'biological methanation'. Turning surplus electricity into stored gas and also into liquid fuels is possible, and probably cost-effective. But techniques are not yet commercially proven at large scale.

UK universities and research institutes have outstanding capabilities in biochemistry. My guess is that the country could built a worldwide lead in the use of living organisms such as archaea and acetogens to convert hydrogen and CO2 into useful renewable fuels. The UK should begin large scale research and development of ‘power to gas’ and ‘power to liquids’ projects to deal with the increasingly likelihood that the Hinkley site will remain empty for ever. The likelihood is that this will enable us to to build a energy system that is cheap, reliable and non-polluting, both here and in other parts of the world.