Eco-economic comparison of batteries and pumped-hydro systems at the micro scale in buildings

Expanding the sustainable energy storage capacity is important due to the growth of renewable energy supplies. As pumped storage and utility-scale batteries are two important methods of energy storage, this study investigates the sustainability of micro pumped storage (MPS) units compared to lithium-ion (Li-ion) batteries for electricity storage. The analysis focuses on the levelised cost of storage (LCOS) and levelised embodied emissions (LEE) for small-scale energy storage solutions within the Australian context. This research aims to identify MPS configurations that are economically and environmentally competitive with Li-ion batteries, determine the minimum rooftop area for MPS efficiency, and assess MPS energy storage capacity at an urban scale. The analysis includes three upper water storage options: Modular Tank (T), Green Roof (GR), and Blue Roof (BR); and two lower storage configurations: Modular Tank and Nearby Stream (S). These configurations are coded by the notation: upper storage type/lower storage type, and are evaluated across buildings of varying heights. The results show that MPS has a significant economic advantage over Li-ion batteries as storage capacity increases, particularly in configurations applied T for upper water storage. MPS outperforms Li-ion in buildings over 150, 50, 100, and 50 m height for T/T, T/S, GR/T, and GR/S configurations respectively. Environmentally, MPS configurations generally have lower LEE than Li-ion batteries, with GR setups demonstrating the most significant benefits, while BR configurations have higher emissions. The study also identifies the minimum rooftop area required for MPS installations to be viable, showing that incorporating nearby streams can enhance the feasibility of MPS in buildings with smaller rooftops. However, the findings reveal that MPS systems are generally less advantageous than battery systems for buildings with rooftop areas smaller than 1,175 m2. Finally, despite only up to 28 buildings in Melbourne meeting the optimal MPS criteria, the ability to store up to 14 MWh/day confirms MPS as a viable, sustainable alternative to Li-ion batteries under specific conditions, contributing to global sustainable energy efforts.