AbstractIncreasing renewable energy generation influences the reliability of electric power grids. Thus, there is a demand for new technical units providing ancillary grid services. Intermittent renewable energy sources can be balanced by energy storage devices, especially battery storage systems. By battery systems grid efficiency and reliability as well as power quality can be increased. A further characteristic of battery systems is the ability to respond rapidly and precisely to frequency deviations, making them technical ideal candidates for primary control provision (PCP). PCP by battery systems is applied in form of positive (discharge mode) and negative control (charge mode) and can reduce must-run capacity of fossil power plants.In this study environmental impacts of PCP by novelLi-ion large-scale battery energy storage systems (BESSs) are compared to impacts of PCP by state-of-the-art coal power plants (CPPs) using a Life Cycle Assessment (LCA) approach. An inventory of all relevant inputs (resources, material and energy flows) and outputs (emissions, wastes and waste water) is compiled. Environmental impacts associated with these inputs and outputs are evaluated. Finally, PCP by BESSs and fossil power plants are compared in terms of environmental performance. Different scenarios are analyzed by varying sensitive parameters like efficiency loss due to PCP at fossil power plants and required must-run capacity for PCP.