By combining the advantages of different energy storage technologies, the hybrid energy storage system (HESS) can satisfy the multiple requirements of prosumer systems. However, the required capacity of the HESS is larger than that of the single-battery energy storage system (ESS). This paper investigates the energy exchange within the HESS caused by the phase shift of the low-pass filter controller and its relevant impact on the HESS. The results show that unnecessary energy exchange results in an oversized capacity and increased energy loss. In addition, the increase in the time constant of the low-pass filter controller leads to a larger phase shift, further contributing to the increases in the total capacity and energy loss. Furthermore, this paper compares the single-battery ESS, the battery-supercapacitor HESS, and the battery-flywheel HESS implemented in a household-prosumer system along with a renewable energy source (RES). The comparison of the ESS combinations demonstrates the differences between their power flows, the required capacities of their individual energy storage devices (ESDs), their energy losses, their battery lifetimes, and their project costs. The results indicate that techno-economic analysis should be performed carefully to select the appropriate ESS solution for specific household-prosumer systems.

A hybrid energy storage system (HESS) consisting of batteries and supercapacitors (SCs) is an effective approach to stability problems brought by renewable energy sources (RESs) in microgrids. This paper investigates the energy exchange between the two energy storage devices (ESDs) caused by the low-pass filter (LPF), which leads to the oversized capacity of HESSs. In addition, the energy exchange between the ESDs leads to more energy loss of HESSs. Based on the analysis of the power flows, this paper proposes an improved controller based on the LPF controller. A power direction control strategy eliminates the non-beneficial power flow to reduce the capacity of HESSs and improve the round-trip energy efficiency. In addition, a SOC control strategy regime balances the desired state of charge (SOC) of the ESDs instead of depending on the LPF. In this paper, the case study shows that the improved LPF controller reduces the capacity of the HESS to the minimized capacity and improves the round-trip energy efficiency. Furthermore, it has no adverse effect on battery aging and achieves the battery lifetime extension with a smaller capacity. A scaled-down HESS experimental setup validates the effectiveness of the improved LPF controller and the simulation results. Finally, the proposed improved controller is compared with various existing controllers to verify the performance.

To promote the development of renewables, this article evaluates the life cycle greenhouse gas (GHG) emissions from hybrid energy storage systems (HESSs) in 100% renewable power systems. The consequential life cycle assessment (CLCA) approach is applied to evaluate and forecast the environmental implications of HESSs. Based on the power system of Sweden, different HESS combinations, which include energy storage (ES) technologies: pumped hydro ES, hydrogen ES, lithium-ion (Li-ion) batteries, lead-acid (PbA) batteries, vanadium redox (VR) batteries, supercapacitors (SCs), and flywheels, are discussed. The results show that for Sweden and similar large-scale utility applications, the cradle-to-gate GHG emissions from the HESS contribute to a major share of the life cycle GHG emissions due to the under-utilization of the cycle life. Among the HESSs compared in this study, the Pumped hydro+Li-ion+Flywheel combination exhibits the least life cycle GHG emissions. Moreover, the phasing out of nuclear power brings a severe challenge to the carbon reduction target. However, the introduced HESS manages to reduce GHG emissions from a 100% renewable power system.

In recent years, driven by global environmental issues, a growing number of renewable energy sources (RESs) have been developed. Microgrids have been confirmed as an important part in the increasing penetrations of renewable energy and the shift from a centralized paradigm to decentralized electricity production. The energy storage system (ESS) is a critical component that affects the development of microgrids. Combining advantages from different energy storage technologies, a hybrid energy storage system (HESS) can satisfy multiple requirements in microgrids. This paper compares the single battery system with the battery-supercapacitor (SC) HESS and the battery-flywheel HESS in an isolated photovoltaic (PV) power microgrid. Results show that both the SC and the flywheel distinctly reduce the battery charging and discharging powers and the required capacity of the battery. Therefore, the stresses and the needed size of the battery are reduced and the battery lifetime is extended.

A critical issue in a hybrid energy storage system (HESS) is the control strategy, especially the power distribution between the individual energy storage devices. In this paper, the power distribution strategy based on the low-pass filter (LPF) controller with a variable time constant is introduced. The adjustable range of the variable time constant is determined by the spectrum analysis of the imbalanced power in a stand-alone household-prosumer system. In addition, the variation of the time constant is based on the feedback of the state of charge (SoC) of the supercapacitor (SC). The simulation results show that the power distribution strategy keeps the SoC of the SC in a moderate range and utilizes the SC more properly. A scaled-down experimental setup is built to verify the effectiveness of the power distribution strategy and the simulation results. Therefore, the proposed power distribution strategy ensures the effective operation of the HESS, avoids the unnecessary enlarging of the SC, and achieves cost reduction.