This paper investigates the potential for use of batteries from retired plug-in hybrid electric vehicles (PHEVs) in specific grid applications. In this study, project, a reference capacity test was performed to check the state of health, state of charge (SOC) and battery durability of a PHEV battery, and the pack was then tested under duty cycles for different grid applications to determine whether it would satisfy such applications in technical terms. The duty cycles considered are peak shaving, frequency regulation, photovoltaic (PV) smoothing and renewable energy firming. The data show that the battery can satisfactorily fulfil the requirements of peak shaving applications in terms of stability and battery retention capacity, and that the requirements of the frequency regulation service are also partially met. The untracked time for the battery signal was 4% (slightly exceeding the condition set for passing the tracking test, which is 2%). The SOC and temperature were within permitted limits. The battery, however, did not achieve good performance for PV smoothing or renewable energy (RE) firming. The untracked times were 14% and 11% for PV smoothing and RE firming, respectively (greatly exceeding the 2% condition for passing the tracking test). The SOC and temperature for the PV smoothing were within acceptable limits. The pack failed to complete the RE firming cycle as the SOC reached maximum safety limits after 6 h and 23 min, whereas the duty cycle is 10 h long.

This research presents the performance evaluation of four various types of top‐of‐the‐line commercial and prototype lithium‐ion energy storage technologies with an objective to find out the optimal cell technology, which is suitable for the development of high power battery packs for regenerative braking systems applied in next‐generation demonstrator platform vehicles. The novel porotype lithium‐ion cell technology is developed using linear combined nanofibers and microfibers battery separators laden utilizing wet nonwoven processes compared to the dry process laden multilayered porous film separators in commercial cell technologies. The performance comparison of all technologies has been conducted both at “cell‐level” and “pack level” through the study of internal performance parameters, such as capacity, resistance, self‐discharge, and battery temperature rise. This study also encompasses the differences in using external pack assembly and/or development parameters like the number of cells which are required to develop the pack, pack mass, pack volume, and pack cost. Both the internal performance parameters and external pack assembly and development parameters have revealed that novel prototype cell technology is the most optimal technology among all four cell technologies for regenerative braking systems, which have been investigated during this research. The novelty of this work is the development of novel prototype cell technology and its performance comparison with commercially available cell technologies used in regenerative braking systems of the latest hybrid/electric vehicles, which is in line with global initiatives, such as UK/EU transition to EVs and UN sustainability goals. The significance of this work in terms of high power pack development for regenerative braking of next‐generation vehicles is evident from various industrial applications. This work will influence decisions for both battery testing techniques and accurate battery comparison methods for automotive, locomotive, aerospace, battery manufacturers, and wind turbine industries.