Environmental performance of electricity storage systems for grid applications, a life cycle approach

The environmental impacts of storage technologies are often neglected and not part of the selection and decision making process. In this paper, the environmental performance of suitable storage technologies for grid applications is assessed. Using a life cycle assessment methodology we analyze the impacts of the construction, usage and disposal/end of life of each of the studied systems. Pumped hydro and compressed air storage are studied as mechanical storage systems and advanced lead acid, sodium sulphur, lithium-ion and nickel-sodium-chloride batteries are addressed as electrochemical storage systems. Hydrogen production from electrolysis and subsequent usage in a proton exchange membrane fuel cell is also analyzed. A characterization of the systems is performed and includes already implemented storage units throughout the world as strong examples and test subjects. The functional unit is one kWh of energy delivered back to the grid, from the storage system. The environmental impacts assessed are climate change, human toxicity, particulate matter formation, and fossil resource depletion. Different energy mixes are used in order to mimic scenarios where the environmental applicability of the technologies is put to the test. Results indicate that the performance of the storage systems is tied to the electricity source used during use stage. Renewable energy sources have lower impacts throughout the use stage of the storage technologies. Using the Belgium electricity mix of 2011 as benchmark, the sodium sulphur battery is the best performer for all the impacts analyzed. Pumped hydro storage follows in second place. Regarding infrastructure and end of life, battery systems have higher impacts than mechanical ones because of lower number of cycles and life time energy.