ENERGY MANAGEMENT SYSTEM (EMS) ELABORATED

Energy Management Systems (EMS) have become a hot topic of discussions as we move towards reliable renewable energy resources. Currently there’s a lot of confusion floating around with respect to the functionalities of EMS. In this article we’ll provide some insight on EMS functionality and capability, relevant to Energy Storage Systems (ESS) and renewable energy projects.

 

In general terms, according to UNIDO and International Organization for Standardization (ISO), Energy Management System (EnMS) involves developing and implementing an energy policy, setting achievable targets for energy use and designing action plans to reach them, measuring progress. This might include implementing new energy-efficient technologies, reducing energy waste, or improving current processes to cut energy costs.

Apart from improving efficiency of existing systems and optimizing utilization of energy resources, moving the power grid to 100% renewable energy resources is the need of the hour, and sooner the better. The rapid development and implementation of renewable energy resources is posing greater challenges due to intermittent and random nature of wind and PV-Solar. Battery energy storage systems (BESS) have been considered as an effective resource to mitigate intermittency and variability challenges of renewable energy resources.

EMS in context with renewable energy generation plants, where Battery Energy Storage System (BESS) is used for providing required stability, resilience, and reliability, is a supervisory controller that dispatches one or more energy storage/generation system(s). It’s required to monitor and optimize charge-discharge cycles of each energy storage system, as well as to provide interoperability to interface multiple energy storage and generation systems.

EMS  addresses two main engineering challenges faced in efficient operation of large-scale energy storage systems:

  • Optimized scheduling of grid energy storage to guarantee safe operation while delivering the maximum benefit.
  • Coordination of multiple grid energy storage/generation systems that vary in size and technology. It is common for the subsystems of an energy storage system to be made by different manufacturers. Therefore, one of functions of EMS is to provide interoperability and coordination within their operations. 

Wherever BESS is a standalone system, the energy management system (EMS) is the link between the grid demand and the Battery Management System (BMS). It continually monitors grid requirements and accordingly facilitates transfer of energy to/from the BESS, by utilizing control logic. The EMS sends an input signal to either charge or discharge the batteries, depending on the control logic requirement, and the State of Charge (SOC) or State of Health (SOH) of the battery system.

 

An EMS can also act as an overall energy management system that balances multiple generation resources based on grid requirements. In a PV-Solar + BESS setup, an EMS can balance the outputs from PV-Solar and BESS simultaneously. It can dictate when to start discharging the batteries to pump stored power to the grid, and when to stop discharging and start charging again, based on production scenarios or customer agreements. The EMS can also be programmed to decide whether the battery system should be charged from the PV resource or from the grid.

 

According to The World Bank report on Economic Analysis of Battery Energy Storage Systems May 2020 achieving efficiency is one of the key capabilities of EMS, as it is responsible for optimal and safe operation of the energy storage systems. The EMS system dispatches each of the storage systems. Depending on the application, the EMS may have a component co-located with the energy storage system (Byrne 2017).

There are some who have tried to classify EMS as only being an analytical tool for the BESS, along with fancy terminologies like cloud storage and controls. The question needing to be asked is, does the industry feel safe/comfortable having cloud based data storage and controls for s these vital power generation plants, done from random locations around the globe?

The truth of the matter is that EMS can have analytical capabilities but primarily the EMS is the system-level controller:

  • Located at the interface between the BESS, the application, and the system owner
  • It acts like the brain of the storage system

From external signals or objective functions, the EMS is responsible for:

  • Dictating the power flow in and out of the BESS
  • Distributing the load between the sublevels
  • Communicating the overall state and performance of the system

The EMS can be integrated within a Supervisory Control and Data Acquisition (SCADA) solution, to build a multi-sourced system.


The BMS monitors, controls, and protects the successive layers of the battery, from the cells to the banks to implement the instructions of the EMS. BMS is often built in a master-slave configuration with a master BMS (e.g., rack BMS) controlling multiple slave BMSs (e.g., Modules BMS). The highest level of the BMS would then report directly to the EMS.


Power Conversion System (PCS) is the interface between the electrochemical storage (battery system) and the grid. The main task of the PCS is thus to transform the power from AC (grid side) to DC (storage part) and vice versa. Even if conversion equipment is more robust, it still needs to communicate with the EMS to report on its status and to perform its basic operational functions such as adjusting the power output (active vs reactive power), detecting, and protecting the system from external faults.


Overall success of EMS is greatly dependent on the field network communication system in place. A strong field network facilitates communication of good quality and reliable data between the EMS and field IEDs including BESS. Reliable data helps the EMS dictate appropriate instructions to meet POI requirements, based on the site specific LGIA/PPA. The EMS ensures optimization of BESS capabilities, within the limits prescribed by the BESS manufacturer, along with other generation resources.

The Energy Management System (EMS), amply supported by a robust field network communication system, is critical to optimizing the overall system safety and enabling high-efficiency operation of the power system. As the grid transitions to more renewable energy resources, BESS can help optimize this transition with required stability, resilience, and reliability. Similarly, custom built EMS, apart from synchronizing multiple energy generation resources to meet POI requirements, can help optimize the BESS services like Energy Time Shifting (Arbitrage), Renewable Capacity firming and Ancillary services like Fast Frequency Response (FFR), AVR etc. EMS can also facilitate requisite charging/discharging data log for ITC compliances.

Nor-Cal’s core competencies include integration of custom control schemes and network architecture configuration. This proficiency makes us well positioned to support any Solar + Storage, or standalone Solar or Storage projects, with expertly designed SCADA Systems, EMS, and Field Network Communication systems to meet your project specific requirements.

We facilitate web-based HMI and feed data via OPC/UA/DNP3/Modbus for any analytical requirements. Schedule a call today to discuss your long-term project goals.

Nashvinder Singh

Written by Nashvinder Singh