Voltage-source converters (VSC) have been widelyutilized to provide instantaneous reactive power support topower systems, an application referred to as static synchronouscompensator (StatCom). The integration of energy storage (ES)into a StatCom makes it possible for the StatCom to provide acertain amount of active power as well as reactive power support.The possible benefit of the additional active power of aStatCom can be power oscillation damping capability, mitigationof phase-jump-related disturbances, etc. Direct connection ofan ES device to the dc link of the VSC incurs an unnecessarilyhigh-voltage rating of the VSC due to the considerable voltageswing associated with the ES device. Dual thyristor convertertopology has been proposed as the interface between the ES andthe dc link of the VSC. In this paper, a cost estimation for systemswith the proposed interface topology is presented regarding threetypes of ES: capacitors, supercapacitors, and batteries. The studyshows potential cost savings with utilization of the proposed interfacetopology. In addition, a cost comparison between differenttypes of ES is presented, providing a guideline for the choice of ES in these kinds of applications.