Grid Resilience and Distributed Energy Storage Systems

By Hamidreza Nazaripouya

In recent years, extreme weather events, and cyber-physical attacks introduce new vulnerabilities to the power system. To this end, improving the grid resilience to withstand and recover from disruptive events and minimize the duration, intensity, and the negative impacts of unfavorable events is imperative. Energy storage systems can be considered as one of the key components for improving the power resilience of the electrical grid. The application of utility-scale energy storage to enhance the local grid resilience and mitigate the impact of generation loss during emergency events has been significantly discussed in academic publications as well as industrial and federal reports. Some sample projects include Vermont-Rutland project with 4MW battery that provides resilient power for a public emergency shelter, and Massachusetts-Sterling project with 2MW/4MWh battery storage, which provides emergency backup power at the time of power outage to critical facilities. Recently, the deployment of behind-the-meter (BTM) energy storage and Electric Vehicles (EV) has grown rapidly. It is expected that the overall BTM segment in the U.S grows from 19% of the 2016 storage market to 52% by 2022. The plug-in EV market in U.S has also grown from around 30,000 vehicles in 2011 to 1,138,400 in 2018. Merging and proliferation of distributed stationary energy storage as well as mobile energy storage (e.g. Electric Vehicles) in the power systems, creates new opportunity for network of distributed energy storage units to contribute to the grid resilience at larger scale. This article will study the role of distributed stationary and mobile energy storage to enhance the grid resilience.

Under normal conditions, each stationary or mobile energy storage unit operates as usual in the power system. That is, EVs purchase electricity from the grid to be charged for the next trip, or they exchange energy with the grid and provide ancillary services when they are not used for transportation. Stationary storage systems are also locally controlled to participate in electricity market, demand side management, or microgrid operation. During unusual grid events, like extreme weather, cyber-physical attacks, or sudden changes in renewable generation or loads, a network of energy storage units can be properly managed to improve grid resilience by restoring load and energizing the grid, optimizing energy resource utilization, maintaining supply-demand balance, and avoiding instability in the grid. A network of distributed energy storage systems can aid restoration and re-energizing of systems by facilitating the operation of system in islanded mode or compensating for the loss of the main power source through releasing the stored energy in a coordinated manner. Also, integration of distributed energy storage in a grid enhances the flexibility of grid for immediate reconfiguration in response to unforeseen events. The network of energy storage units can be managed to control the power flow in the new network configuration and reroute the stored energy into critical infrastructure.

The energy storage units can also act as an energy buffer to compensate renewable intermittency. Therefore, the incorporation of energy storage systems with renewable energy resources like solar and wind turns renewable generation into a reliable source for providing power during grid outages.

At the time of disturbance, distributed energy storage units are characterized as dispatchable generation and load, which provide extra flexibilities for relaxing the constraints in supply-demand balancing problem and optimizing the energy resources utilization. In addition, fast response energy storage units can quickly mitigate the disturbances locally and prevent the propagation of disturbance effect in the system.

Energy storage systems owing to the amount of energy they store offer virtual inertia to grids. That is, the energy stored in the storage units emulates the kinetic energy stored in the rotor of synchronous generators which can be released in the events of disturbance or drastic power imbalance. The virtual inertia of distributed energy storage units enhances the stability of the system at the time of sudden loss of the main generation, and thus increases the tolerance and robustness of the entire system to sudden changes. Although distributed energy storage systems can effectively contribute to grid resilience, there are still several challenges to enhance the grid resilience by utilizing a network of distributed stationary and mobile energy storage systems. The challenges can be categorized in 1) technological challenges 2) financial and economic challenges 3) policy and regulation challenges. The technical concerns are mainly associated with cooperative control of energy storage units across the network for providing fast response to contingency events, with reconfiguration capability and flexibility of the grid, with communication architecture and protocols for interaction between energy units and control system, with interoperability standards, and with battery degradation issues in EVs. The main financial-economic challenges are related to the need for a proper business model, a mechanism for financial transactions between stakeholders (owners, operators, aggregators, etc), and an economic model for cost effective operation of system. Finally, appropriate policies and regulations are required to create resilience service products in wholesale markets, define rate policies and tariff, and outline interconnection regulations and standards.