Economics of innovative high capacity-to-power energy storage technologies pointing at 100% renewable micro-grids

Intermittency and unpredictability of variable renewable energy sources, as well as the mismatch between generation and users' demand, are the major hurdles to overcome looking at 100% renewable grids. Energy storage (ES) technologies are the answer to this question, yet high market costs are still compared to market parity. For the possibility to decouple capacity and power, hence tailoring the energy storage features according to the main functions required, the solutions investigated are based on Vanadium Redox Flow Batteries (VRFBs) and Reversible Solid Oxide Cells (rSOC). In low interconnected micro-grids, the decoupled sizing of capacity and power is an essential feature to attain higher cost-effectiveness. Current metrics for the economics of renewable energy storage fail to a large extent in assessing the value of stored energy, especially when the power source is scarcely predictable. This paper presents improved techno-economic metrics to compare high capacity-to-power ES technologies for renewable-based micro-grids. The new metrics synthetically translates energy efficiency and quality of system integration into monetary terms, going beyond the classic definition of Levelized Cost of Electricity (LCOE). Then, they provide a tool to understand where the main causes of payback deferral stand. For the case-study analysed, different storage assets (VRFB, rSOC and hybrid rSOC) for installations in households featuring 25 kWh bulk capacity and 1.5 kW discharging power are evaluated. The LCOE is equal to 0.438(sic).kWh(-1), 0.739(sic).kWh(-1) and 0.769(sic).kWh(-1) for VRFB, rSOC and hybrid rSOC respectively. Yet, considering the unit of stored energy, the hybrid rSOC storage system is more convenient than the basic rSOC (2.05(sic).kWh(-1) versus 2.61(sic).kWh(-1)), but far less cheap than VRFBs (0.560(sic).kWh(-1)).