Batteries in Great Britain are cycling more than ever, delivering more energy than before, and some are approaching a decade of operation. All of these things contribute to degradation - which then impacts the revenue potential of battery energy storage.
So, just how far have batteries in Great Britain degraded?
Battery degradation refers to the reduction of a battery’s energy capacity over time. As lithium batteries are charged and discharged, chemical and physical changes occur inside them. These can reduce the battery’s ability to store energy.
You can find out more about battery degradation in our article here.
The environment in which a battery is stored and how a battery is used can affect how quickly a battery degrades. For example, how much the battery has cycled, how far the battery discharges, and at what power the battery discharges.
The more a battery degrades, the less energy it has to provide in the wholesale market, Balancing Mechanism and frequency response services. This limits the usefulness of the battery and its revenue-generating potential. To overcome the impact of degradation batteries can be augmented.
There is no publicly available data that states how far a battery has actually degraded, so we have created an estimate using available metered generation data.
How have we estimated degradation for batteries in Great Britain?
Metered generation data for Balancing Mechanism-registered batteries states how much power a battery has exported or imported within each settlement period. We have used this dataset to calculate the total energy exported by batteries before charging.
Recording the change in maximum exported energy over time can create an estimate of degradation. This was performed first at a monthly granularity and then yearly, with the number of cycles between recordings also calculated.
Degradation has been estimated as the % reduction in maximum exported energy compared to a reference point, defined as the highest recorded exported energy.
Limitations and assumptions:
This method is limited as:
- Some batteries may not have exported their full energy capacity due to participation in frequency response services such as Dynamic Containment. This means there were limited examples of batteries performing a full depth of discharge before charging again.
- Newer batteries, which may have participated more often in high-energy services, do not have as many years of operation to compare.
This reduced the amount of data available. However, aggregated across the fleet it can still provide a view of what battery degradation looks like in reality.
Some batteries may have lost up to 13% of energy capacity through degradation
Based on the estimated degradation data, batteries performing 365 cycles, or one cycle a day for a year, have degraded by 4.4% on average. This is in line with expected degradation curves from industry.
The Modo Energy Forecast degradation curve uses a combination of user-submitted data and manufacturer curves. The batteries indicated by points above this line are degrading slower, while the batteries below are degrading faster.
The system with the highest estimated degradation has had a 12.9% reduction in maximum exported energy after 526 cycles. Based on this curve, it would have degraded 11% after 365 cycles.
The cycles shown in this chart represent the early stages of a battery’s expected cycling over its lifetime. Some warranties are based on the battery performing as many as 10,000 cycles.
Batteries performing higher depth-of-discharge cycles than ever before
Depth of discharge refers to how much of a battery’s energy capacity is used before charging. On average, in 2024, batteries discharged up to 18% of their full energy capacity before charging. Between 2020 and 2022, batteries only discharged up to 8% of their full capacity before charging. This is because they were mostly delivering Dynamic Containment, a low-energy, low-cycling service.