Authors’ reply
We would like to thank Mr Stephens for looking into energy output from future UK wind farms, when there are anticyclonic conditions over the UK. He has kindly provided us with his data which shows that, unless wind farms are placed intelligently, there will be a real problem. As he says, from 180 GW of capacity, under these conditions all that might be expected would be something of the order of 4 GW. But first we would like to address the final sentence in his first paragraph which states: ‘Surely, if this is the case, then a base load of nuclear power could exist alongside wind power and all existing fossil plants could be phased out?’2
This actually is the heart of the matter. Let us suppose we have 20 GW of nuclear and 100 GW of wind energy, with the nuclear operating, night and day, as base load generators. As Michael Laughton has shown in the book Renewable Electricity and the Grid3 on windy days we could expect to have in excess of 50 GW of wind energy. What then does a nuclear plant do? It cannot easily be shut down and then restarted in the same way as a coal or gas-fired plant. Conversely, as Mr Stephens has shown, wind energy could fall to below 3 GW with this amount of wind capacity. This would leave the country very short of power. So we reiterate that nuclear and wind are incompatible.
But it is the latter part of Mr Stephens’ discussion, about anticyclonic conditions, which has helped move the debate forward. It is fairly clear that even when very large wind farms are intelligently located, there will be more of a problem than we anticipated. This gloomy view is also supported by Michael Laughton, who has looked into the issue of providing spare capacity.3 In the medium term this can only come from standby fossil plant and obviously becomes more of an issue as the amount of wind energy increases. In the longer term, energy storage and high voltage interconnecters from Europe will be a solution.
What is missing from this debate is how often standby fossil plants will need to operate, and how frequently they will need to start up. As the amount of wind capacity increases, power plants will run for shorter periods, burning less fossil fuel, but having to start up and shut down repeatedly. This should not require any new capacity to be built. Existing units could stay in service. At some point, the coal-fired units could run on biomass, and combined-cycle gas turbine could be converted to operate on hydrogen.
However, any coal-fired plants that are operating in the future will have been built during the next 15 years, and here there are some questions. The concept is to get the highest efficiency, and make the designs ‘capture ready’ for carbon dioxide emissions. High efficiency is vital to make carbon dioxide capture economic, and implies high pressures and temperatures. Materials and components will be pushed to the limit.4 With such designs stop–start operation is not conducive to high reliability. Furthermore, it seems difficult to envisage carbon dioxide capture systems which can operate satisfactorily under such a ‘cycling’ regime.
Similar questions arise if fossil plant is expected to provide the daytime generation that base load nuclear will find hard to provide. Once again we are in a situation where fossil plants will be in a stop–start situation. In short, the issue of fossil plant economics and maintenance, in either a renewable scenario, or in that of a base load nuclear, should be a dominating question for designers and operators alike. Sadly it is not. As in most other discussions about the future of power generation, whether from wind, fossil, nuclear, combined heat and power, micro generation, and so on, the rest of the system is expected to make good the deficiencies of the concepts that are being zealously promoted by their adherents.
