EMS, BESS and solar: three concepts, one system
How do a solar plant, battery storage and an energy management system work together? The basics, from an automation engineer's point of view.
The area I most want to grow in lately is energy systems. Solar (PV), battery energy storage (BESS) and the energy management systems (EMS) that run them are tightly linked. In this post I summarise the three concepts and how they work together.
Solar (PV)
Solar panels produce variable power throughout the day: low in the morning, high at noon, zero in the evening. When a cloud passes, output can drop within seconds. That's the core issue: production doesn't always line up with consumption.
Battery energy storage (BESS)
A BESS stores energy when there's a surplus and gives it back when needed. Its main parts:
- Battery modules: Store energy chemically (today mostly LFP lithium).
- BMS (Battery Management System): Monitors cell voltages, temperatures and state of charge (SoC) and protects the battery.
- PCS (Power Conversion System): A bidirectional inverter converting the battery's DC to the grid's AC and back.
BMS and EMS are often confused: the BMS manages the inside of the battery, the EMS manages the battery's role in the system.
Energy management system (EMS)
The EMS is the system's "brain". It monitors PV output, consumption, battery state and grid conditions and answers one question: should the battery charge, discharge or wait right now?
Typical EMS strategies:
| Strategy | What it does |
|---|---|
| Self-consumption | Stores surplus PV during the day, uses it in the evening |
| Peak shaving | Feeds loads from the battery during peaks to cut maximum grid demand |
| Energy arbitrage | Charges in cheap hours, discharges in expensive ones |
| Grid services | Helps with frequency and voltage balancing |
While deciding, the EMS respects limits: the battery's SoC window, maximum charge/discharge power, temperature and battery lifetime.
Where the automation engineer comes in
All of these systems have to talk to each other. PV inverters, BMS, PCS and meters usually expose data over Modbus TCP. In substations and large plants, protocols like IEC 61850 and DNP3 take over.
Behind an EMS there are familiar things: collecting data from field devices, running control logic, managing alarms and showing everything on a SCADA screen. That's why PLC and SCADA experience transfers so naturally to the energy sector.
Next, I plan to dig into IEC 61850 and BESS control strategies and share what I learn here.