What has COVID-19 taught us about grid decarbonization?

COVID-19 is a harsh reality that we are all still living with. But interestingly, this unprecedented situation can teach us valuable lessons about a service that has little to do with healthcare: electricity. A case of particular interest is Great Britain, an island that experienced a severe lockdown from 23 March 2020 which lasted for almost three months. The lockdown had an effect never seen before on the electricity system: zero-carbon sources were by far the main source of power. But it posed certain challenges which might become even more evident with the decarbonization of the grid in the future.

This first lockdown – Great Britain is now coming out of its third – was a record-setting period. Great Britain saw the lowest national demand ever recorded, 13.4GW overnight on Sunday 28 June 2020 (in comparison, the lowest demand in 2019 was 18GW). Also, the lowest carbon intensity ever, was on 24 May 2020, when just 46gCO2/kWh were produced on the transmission network. And the longest coal-free period since the industrial revolution, 68 consecutive days from April to June 2020.

Renewables and nuclear plants were the main sources of generation during the lockdown. This was due to the drop in demand, which caused a subsequent drop in prices in the wholesale electricity market. Renewables and nuclear are somewhat indifferent to prices, as they have low or even zero fuel costs. But operating an electricity system simply relying on renewables and nuclear units is not currently feasible. This generation mix lacked flexibility.

To obtain more flexibility, the energy system operator in Great Britain, National Grid ESO, took a number of “stability actions”. The most common stability action consists in turning on a number of gas plants, which increase the flexibility of the grid. These were plants that had not been successful in the wholesale energy market, since their cost was too high for the low levels of demand that we experienced. Therefore, National Grid had to re-adjust the generation dispatch so that it contained enough flexibility to support the temporary grid decarbonization: in other words, gas plants were paid simply to make sure that Great Britain was able to always maintain the balance between demand and generation on a second-by-second basis, but not because they were needed to produce power. The total cost of these stability actions exceeded £300 million during Great Britain's spring lockdown, a three-fold increase compared to the same months in 2019. This means that British electricity consumers had to pay a significant share of their bill for flexibility services, not for energy.

But what exactly is this "flexibility" that is provided by gas plants but not by renewables? The key difference between these two types of generation is a simple concept: inertia. Inertia refers to the rotating masses in thermal generators (like gas and coal-fired power plants), which naturally store kinetic energy as they rotate to produce the power that we consume. These masses are therefore a valuable energy buffer, that spontaneously releases this energy if there is a sudden generation-demand imbalance. Renewables, on the other hand, do not naturally contribute to the inertia of the system, which is why they increase the challenge of maintaining the power balance in the grid. Inertia allows us to avoid blackouts, an ever more critical need as we become increasingly reliant on electricity.

In the future, procuring this flexibility will become even more expensive, as thermal plants will be scarce after grid decarbonization. As shown in Figure 2, stability actions could represent 15% of the total cost of operating the grid by 2030. But new devices like battery storage could provide much more effective stability support, as they are controlled by power electronics converters that can provide very fast power injections to the grid in the event of a generation-demand imbalance. Our recent studies show that a higher capacity of batteries providing support could drastically reduce the cost of stability actions, as shown in Figure 3. And not only the cost would be lower: we would avoid emissions related to stability, as turning on gas plants simply for inertia is not only expensive but also pollutes significantly.

The COVID-19 lockdown demonstrated a clear change of paradigm in electricity grids: the future grids dominated by renewables and lacking inertia will have very fast dynamics, as compared to the past grids dominated by large thermal generators. This is both a challenge and an opportunity: changes will happen much faster, but we also have the chance to react to them much quicker. The future of grid decarbonization will be fast like a Ferrari, unlike its predecessor which is more like a truck. This means we will need a fundamental change in the way we operate the grid: let’s take full advantage of our Ferrari and not drive as if it were a truck.