How green is energy storage? Learnings from a CESI-funded case study

Academics funded by the EPSRC National Centre for Energy Systems Integration (CESI) in the Centre’s first Flexible Funding Call, recently published the results of a study on the impacts of energy storage operation on greenhouse gas emissions, in the journal Applied Energy. Their work is summarised here by the lead author, Dr Andrew Pimm, and the full paper [1] is freely available to all on the journal website. The research team was led by Prof Tim Cockerill of the University of Leeds, and also included Dr Jan Palczewski of Leeds and Dr Edward Barbour of Loughborough University.

About the author: Dr Andrew Pimm

Dr Andrew Pimm is a Research Fellow at the University of Leeds investigating the techno-economics of energy storage, energy flexibility, and industrial decarbonisation. Prior to joining Leeds in 2015, he worked on the development of grid-scale energy storage technologies at the University of Nottingham, where he was involved in offshore trials of underwater compressed air energy storage.

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Energy storage will be a key part of the future energy system, allowing the deployment of higher levels of non-dispatchable low carbon electricity generation and increased electrification of energy demand for heating/cooling, transport, and industry.

Passing energy through storage inevitably results in losses associated with inefficiencies, however previous investigations have found that operation of electricity storage can result in increased CO2 emissions even if the storage has a turnaround efficiency of 100% [2]: if the output from a relatively high carbon source (such as unabated gas or coal) is increased to charge the storage, and the output from a relatively low carbon source is reduced when the storage is discharged, then the result will be a net increase in CO2 emissions.

However, these effects had not been considered recently for Great Britain, and little attention had been given to the extent to which they vary by location. We sought to fill this gap in the knowledge through our study.

We made use of data from National Grid’s regional Carbon Intensity API and ELEXON’s P114 dataset to determine the source of electricity consumed in each of Great Britain’s 14 electricity distribution zones for each half-hour period in 2019 (annual sums shown in Figure 1).

Figure 1: The share of electricity consumption by region and source in Great Britain in 2019.

With these data, we used linear regression techniques [3] to calculate half-hourly “marginal emissions factors” for each distribution zone. These tell us the change in CO2 emissions that occurs as a result of a change to grid electricity demand, disaggregated by time and location. These regional marginal emissions factors were then used to assess the impact of electricity storage operation on grid CO2 emissions in three different storage operating scenarios:

  1. Load levelling, whereby storage is charged at times of low demand and discharged at times of high demand.
  2. Wind balancing, whereby storage is charged at times of high wind output and discharged at times of low wind output.
  3. Reducing wind curtailment, whereby storage is charged using excess wind generation that would otherwise be curtailed and discharged at times of high demand.

The resulting emissions reductions are shown for selected distribution zones and Great Britain as a whole in Figure 2. Wind balancing is the only storage operating mode that leads to increased CO2 emissions, and emissions are reduced the most when storage is operated to reduce wind curtailment in regions with high levels of fossil generation.

Across all regions and operating modes, the difference between the highest reduction in emissions and the highest increase is significant, at 741 gCO2 per kWh discharged, and is roughly equivalent to the reduction in emissions per unit achieved by fitting a coal power plant with carbon capture and storage.

Figure 2: Potential emissions reduction through storage operation for the three operating scenarios, in six selected distribution zones and Great Britain as a whole in 2019.

While electricity storage will be a key component in future low carbon energy systems, our work has shown the importance of storage location and operating mode to its operational emissions and the possible dangers of evaluating emissions using average emissions factors. We are currently using these new techniques to investigate the lifecycle emissions of storage and smart EV charging across the EU.


[1] Pimm AJ, Palczewski J, Barbour ER, Cockerill TT. Using electricity storage to reduce greenhouse gas emissions. Applied Energy. 2021;282:116199.
[2] Denholm P, Kulcinski GL. Life cycle energy requirements and greenhouse gas emissions from large scale energy storage systems. Energy Conversion and Management. 2004;45:2153-72.
[3] Hawkes AD. Estimating marginal CO2 emissions rates for national electricity systems. Energy Policy. 2010;38:5977-87.

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