Q1 2019: How low can we go?

by Dr Iain Staffell – Imperial College London 

Just how low can Britain’s power system go in terms of fossil fuels and carbon emissions? 

Does Britain’s geography necessitate a minimum amount of dispatchable, flexible and thermal power on the system? Being an island, it is more expensive for us to build electrical links to other countries, than it is for example Germany to build them across its land borders. Similarly, our lack of mountains means that pumped hydro is never going to provide weeks or months of storage. Britain faces more challenges than most in this area, but that does not dampen the ambition for zero carbon electricity.

Last month National Grid ESO announced it will be ready to operate a zero-carbon electricity system by 2025. This would mean that as more renewables and nuclear power come online, the power system can be operated safely and securely at times when they are able to supply all demand. With over 43 GW of wind, solar and nuclear capacity already installed and demand averaging 35 GW last year, this situation is already a real possibility. 

Wind, solar and nuclear have provided up to 88.5% of Britain’s electricity at one moment in time. What prevents them going further? The current solution is instead to curtail (or waste) some renewable generation and bring on flexible fossil generators (coal and gas) to keep the system stable. This sends power prices negative and increases emissions, as happened for six hours straight on a sunny, windy day in March. The key problem is that the grid needs many services to run safely: reserve, inertia, frequency response and voltage support to name a few; and these are currently provided by flexible and dispatchable technologies.

All of Britain’s electricity came from flexible and controllable sources (coal, oil, gas and hydro) until the world’s first commercial nuclear reactor opened at Calder Hall in 1956. Over the next four decades this share gradually moved down to 75% as nuclear came into the mix.¹ As shown below, the last ten years have seen a greater change than the previous fifty – this year is set to be the first when less than half of the country’s electricity comes from fully dispatchable sources.

The share of generation from fossil fuels, biomass and hydro ²

The share of controllable generation has fallen by 3% per year over the last decade. National Grid’s Future Energy Scenarios sees this trend continuing into the mid-2020s, as Britain sources more of its electricity from wind and solar, and imports more from abroad. The share of fully-dispatchable British electricity generation may fall to just one quarter in as little as ten years, before settling at between 8% and 21% in the 2040s.

As always, year-round averages do not tell the whole story, and it is the hour-to-hour variation which matters with electricity. Since 2016 the power system has seen periods with less than a quarter of electricity coming from conventional sources (as shown by the red circles). Last year on an August night, a low of 15% was reached, with just 2.4 GW being produced from fossil fuels. The question now is how to squeeze out this last couple of gigawatts of fossil fuels?

This will require a radical departure from the traditional ways of planning, analysing and operating power systems. National Grid ESO has set out a roadmap for achieving this over the next five years: from defining new services and regional requirements to them, building new markets for these services, allowing more technologies into these markets,³increasing the deployment of storage, and using AI to improve the forecasting tools for wind and solar power.

Other system operators at the forefront of renewables integration are trialling their own approaches.  Australia uses mandates: new wind and solar farms must install their own technical solutions (such as flywheels) to provide system services.  California has opted for central regulation: their grid operator decides how much storage (or other flexible solutions) to build and then runs these much like the transmission wires. National Grid ESO is instead taking the market-led approach: defining the need for services and creating the marketplaces for trading them. Their aim is to allow companies to innovate and compete to find out how these services can then be delivered most efficiently. 

Of course, running a traditionally fossil-fuelled power system at zero carbon on average will be much more difficult than running it for half an hour at a time. Ultimately, the aim is not just to cope with single periods. Having the tools and systems in place to run for a single hour at zero carbon will mean the grid is ready and capable to run for longer. Britain quickly moved from seeing the first ever zero-coal hour to having the first day, first weekend, and most recently a whole week without coal. In five years’ time we could well be repeating the same exciting process, but with zero fossil fuels, and zero carbon. To quote Fintan Slye, director of National Grid ESO, “Operating a zero-carbon electricity system in 2025 is a major stepping stone to the full decarbonisation of the entire electricity system”.

1: Note that Britain’s older gas-cooled nuclear reactors are not flexible and cannot reduce output to follow load. Newer water-cooled reactors such as the EPR being built at Hinkley Point C should have similar flexibility to other conventional power plants.

2: Thermal power stations (coal, oil, gas and biomass) and hydro are the technologies which can provide the full set of system services at present.

3: For example, allowing wind and solar to provide reserve and response services from 2020

Authors: Dr Iain Staffell and Julian Leslie