Techno-economic comparison of different hybrid energy storage systems for off-grid renewable energy applications based on a novel probabilistic reliability index

The application of energy storage technologies is crucial to the extensive exploitation of renewable energy for power generation in off-grid areas because energy storage can mitigate the intermittency of renewables and balance the supply-demand mismatch. A hybrid energy storage system (HESS) with two or more heterogenous and supplementary energy storages outperforms single energy storage from the perspective of reliability and cost-effectiveness, but how to select the optimal HESS configuration is still unknown. To this end, this paper investigates the techno-economic comparison of ten HESSs in off-grid renewable energy system applications, including all pairwise combinations of thermal energy storage, pumped hydro storage, hydrogen storage, battery, and supercapacitor. Moreover, a novel probabilistic reliability index called loss of power supply probability with probability of exceedance (LPSP-PoE) is proposed to quantitatively handle the long-term uncertainties of renewable energy resources. The rule-based coordinated energy management strategies considering the charging/discharging priority and optimized operating thresholds are established for different HESSs, and then the multi-objective optimization models aiming to minimize net present cost and LPSP-PoE are developed to search the optimal components sizing and operating thresholds simultaneously. Finally, the results of case studies show that: (1) the optimal net present cost of thermal energy storage-battery at the highest reliability level is 3.3472 billion USD, which is 6.98 %-69.85 % lower than the figure for other HESSs, indicating that thermal energy storage-battery is the most cost-effective HESS configuration; (2) The optimal charging/discharging priority can lead to 29.6 %-75.2 % cost reduction, and the optimal operating thresholds can always achieve the lowest LPSP, illustrating the superiority of the proposed operation strategies; (3) the techno-economic perfor-mance of all HESSs varies significantly with the PoE level and load profile, while their rankings remain basically unchanged, showing the robustness of the comparison results.