Net Zero – it’s all in the balance

18 Nov 2021

The Government’s new target for net zero electricity by 2035 is welcome. One of the biggest challenges will be finding alternatives to fossil fuels with their low cost, large capacity and long duration storage options, which still provide nearly all the flexibility and resilience that balance our energy systems.

We must ensure that truly ‘grid scale’ energy can still be balanced over prolonged timescales. There are currently no easy solutions for this, so all the more reason to ensure the necessary questions are asked and satisfactorily answered when designing a secure net zero system.

Our recent research paper seeks to help frame these questions and aid assessment of the answers by demonstrating the orders of magnitude of balancing services currently involved in the electricity and heat sectors, and simulating how these may evolve under future demand scenarios in a system dominated by wind and solar generation.

Some of the conclusions may come as a surprise:

Overall imbalance levels in a fully renewable system will be higher – No

When we embarked on our research, we initially suspected the imbalance levels of a fully renewable system would increase, with variations in solar and wind generation adding to those from demand fluctuation.

However, our results show similar orders of magnitude for balancing requirements with inter‑day levels up to 3-4 TWh, accumulating to tens of TWh between seasons and well over 100 TWh across years.

Nevertheless, decarbonising heat through electrification would transfer imbalance into the electricity system, doubling or trebling current levels but no longer with ready access to fossil fuel storage to manage them.

Leave solar out of the mix if heat is electrified – Yes

Over a year, wind matches heat demand well. However, solar is anti-correlated, generating most in summer when heat demand is lowest, and little to none in winter darkness when heat demand is highest. If heat is electrified any level of solar adversely impacts on imbalance levels.

Baseload nuclear generation will help deal with imbalance – No

Inflexible nuclear generation makes little or no difference to overall imbalance levels if it is run baseload, i.e. continuously at a constant level. System imbalance then only mirrors demand variation in both scale and pattern. Any ‘positive’ contribution made to managing deficits just leads to a greater surplus to deal with at other times.

Some of the results were more in line with expectations:

There is a loss of reliability if renewable generation replaces fossil fuel plant – Yes

Worst-case scenarios do occur, when days of highest demand coincide with days of lowest renewable generation, and vice versa. The capacity credit – the fraction of firm conventional generation that can be replaced by intermittent renewables without loss of system reliability – can fall as low as 5% over a whole day and such system deficits can accumulate over several days or even weeks while such conditions persist.

Batteries are a technical and economic alternative to fossil fuels for grid-scale balancing – No

Even with the enormous improvements in battery technology they still fall several orders of magnitude short in both available power and its duration when compared to chemical storage, such as currently embodied in fossil fuels. Even if this could be overcome, replacing just a day’s worth of natural gas balancing capability with batteries would cost over £1 trillion.

Finally, it is important to note that gas balancing costs for heat and electricity generation are included in the fuel price. Balancing and associated infrastructure costs are not covered by the levelised or wholesale price of solar and wind generation. Future balancing costs should not be underestimated – what looks like an optimal energy mix based on levelised costs of energy production could look very different to one based on minimising total system cost.

‘Net-zero – keeping the energy system balanced’ was authored by Keith MacLean, Grant Wilson and Noah Godfrey. Access it here.