Grid-scale electricity storage has been identified by MIT Technology Review as one of the 10 most difficult technology problems in the world. spare storage capacity to a cloud-based operator through fixed rental and on-demand payments. The role of the operator is usually played by a third party, which may be set up specifically for the purpose. The system operator could also directly invest in creating a cloud energy storage operator. Cloud Energy Storage Trials In this article, we consider four types of cloud-based energy storage schemes emerging in China. They use different storage resources to provide various flexible services under numerous business models. They are summarized in Table 1. Aggregation of Distributed Storage Systems The Jiangsu power system is one of the largest grids in China. The need for storage resources is increasing due to the rapid development of renewable energy projects and several ultrahigh-voltage dc regional interconnectors that have a capacity of 6,000-8,000 MW each. A cloud-based aggregation platform for distributed storage stations was built in 2018 to support the Jiangsu system. Currently, the project has integrated eight distributed battery stations, as listed in Table 2. All stations use lithium-ion batteries with a depth of discharge table 1. Cloud-based energy storage trials in China. Trial Aggregation of distributed storage systems Distributed storage from a mobile communication base station General Storage Resources Battery storage systems Uninterruptible power supply of data centers and communication base stations Distributed virtual storage from industrial load demand response Distributed storage from a heat network Flexible industrial loads Thermal storage in heat networks Operator Grid company Consumer Peak shaving, frequency regulation, and emergency control Grid company Peak shaving Maturity Demonstration project in operation Demonstration project under construction Third-party company Peak shaving and emergency control Heating company and third-party company Peak shaving Commercial operation Research and experimentation Name Wufeng Mountain SanYue North Mountain ChangWang XinBa DaGang JianShan DanYang Total 66 table 2. Distributed storage stations aggregated by Jiangsu Power Grid. Capacity Location 24 MW/48 MWh 10 MW/20 MWh 16 MW/32 MWh 8 MW/16 MWh 10 MW/20 MWh 16 MW/32 MWh 5 MW/10 MWh 12 MW/24 MWh 101 MW/202 MWh ieee power & energy magazine Investor Spare space outside Wufeng Mountain substation XJ Group Decommissioned 35-kV SanYue substation Spare space in nearby industrial park Decommissioned 35-kV ChangWang substation Spare space in 110-kV XinBa substation Spare space in 110-kV DaGang substation Spare space in 110-kV JianShan substation Spare space in 220-kV DanYang substation Shandong Electric Group State Grid Jiangsu Integrated Energy Service july/august 2021