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Sunnica is proposing to deploy very large scale Battery Energy Storage Systems (BESS) on three sites within the Solar plant. The Sunnica BESS could be one of the worlds largest BESS deployments.

The BESS provides the capacity to store electricity from the Grid when energy prices are low and return that electricity at periods of high demand when prices are high. 

The Sunnica Battery Energy Storage Systems

Sunnica have not yet defined the storage capacity that will be deployed, but they are proposing 3x BESS compounds that will cover about 77 acres in total.  These will house many containers (like shipping containers), measuring up to 17 metres in length and 6 metres in height.

Lithium-Ion battery chemistry is the technology they have proposed to use, which is now the market leader and is widely used in applications such as mobile phones, laptops and electric vehicles.

Grid-scale BESS comprise millions of individual Lithium-Ion cells. These are packaged into battery modules, which are housed in racks, which themselves are densely packed into shipping container sized units.

The image on the left below shows a typical configuration of battery racks in a shipping container, and the image on the right a site with multiple shipping container units deployed. This image shows a relatively small scale deployment; Sunnica's proposal would be considerably larger since their three BESS sites would cover 77 acres in total.


Image courtesy of

Image courtesy of Fluence Energy

Battery Energy Storage Systems


Grid scale Lithium-Ion BESS facilities of this size are relatively new technology.  The regulations governing their safety have not yet kept pace with their deployment.  There have been over 35 incidents of battery 'fires' (thermal runaway events) at such facilities in the last 3 years across the globe.  One of these was in the UK (Carnegie Road, Liverpool) in September 2020.


In certain circumstances (such as physical damage, overcharging or as a result of manufacturing defects) a Lithium-Ion cell can exhibit thermal runaway.

When thermal runaway occurs a cell can get so hot it emits flammable and toxic gasses leading to fire.


This video shows what happens if thermal runaway occurs.

A battery module consists of a large number of individual Lithium-Ion cells. If thermal runaway occurs in one cell, this can cascade to neighbouring cells causing the fire to propagate through the whole battery module.

When cells are tightly packed it is virtually impossible to extinguish the resulting fire. This has happened with battery modules used in electric vehicles as explained in this video.

As well as electric vehicle fires, there have been battery storage container 'fires' such as the one shown in the image on the right.

The real risk is an uncontained thermal runaway if it cascaded to a neighbouring shipping container unit, it could cause a significant incident and would be incredibly difficult to bring under control.

This video shows a battery fire cascading between electric buses parked next to each other and highlights the risk of fire propagation to adjacent structures.


Image courtesy of LI-TAMER

Sunnica Battery Safety Proposals


The Sunnica application contains an Outline Battery Fire Safety Management Plan. This explains how Sunnica intend to build and operate their battery storage facilities and their proposed safety features. Unfortunately the outline plan is of limited value, since the battery technology has not been defined and neither has the proposed BESS compound layout or the likely number of battery containers.  Different technologies have different features, so it is impossible to assess the adquacy of these proposed safety measures with the limited information provided.

Similarly, the lack of information about the precise BESS technology means that any modelling of potential gas plumes that could be emitted if a fire were to occur is also of limited value.

  • Grid scale Li-ion BESS facilities of this size are relatively new. There are currently no established engineering standards that mitigate thermal runaway. Fire Authorities are still learning how to handle such events.

  • Sunnica's impact assessment in the event of a fire occurring is based on a single container fire only.  There have been cases where fires have spread between containers. 

The lack of adequate regulatory standards for Grid scale BESS needs to be addressed urgently. Learning points from past incidents need to be implemented swiftly to stop repeat failures occurring.  And, in general, more needs to be done to ensure that national and local planning authorities and fire services are aware of the potential hazards assocated with Grid scale BESS.

Battery Energy Storage Systems

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