Assessment of Battery Energy Storage Systems

Current and future power grids are characterized by a high share of renewable energy sources. This leads to fluctuations in the power injection that needs to be balanced. A Battery Energy Storage System (BESS) allows for the balance of supply and demand of electrical energy, utilizing stored energy during “peak demand” times and storing energy during times of “low demand”.

From a technological perspective, battery storage is mature and there are hundreds of suppliers providing reliable systems. However, several barriers must be overcome before Battery Energy Storage Systems (BESS) are fully integrated as a mainstream option in the power sector. These include performance and safety issues, regulatory barriers, and utility acceptance.

As BESS technologies are widely used in modern life, there comes a concern on the risks associated with these technologies. Hazard identification can provide information for facility siting and proper design of BESS, and establish emergency response procedures for the battery site and local community.

The main core of the energy storage systems are the battery cells. Lithium-ion cells are sealed units, and under normal usage conditions, venting of electrolyte should not occur. However, if exposed to abnormal heating or other abuse conditions, electrolyte and electrolyte decomposition products can vaporize and be vented from cells. Vented electrolyte is flammable, and may ignite on contact with an ignition source, such as an open flame, spark, or a sufficiently heated surface.

Some protection strategies for fires can in some cases lead to increased explosion risk (e.g. when small fires are suppressed). Selecting a protection strategy that will give the overall lowest risk is therefore an important activity in risk management of BESS. Based on experimental tests DNV GL initially perform phenomenological and risk analyses which in turn are supplemented by structured CFD simulations and experiments as needed. Experimental results from a large set of different tests are essential to understand the potential off-gassing, explosion and fire scenarios setting the limits of the energy release into the scenario.

DNV GL has carried out a series of experiments on lithium ion battery fires at the cell level with different release conditions and ventilation rates to assess the off-gassing associated with a battery exposed to a fire condition or undergoing runaway reaction. Based on the battery fire testing data, we are presenting a hazard assessment associated with battery failure mechanism of BESS in this paper. Various scenarios will be discussed regarding different battery chemistries, capacities and site designs.