ESS Architecture
An Energy Storage System (ESS) is more than batteries. Here are the blocks and how they connect.
The building blocks
- Battery modules → rack: series/parallel LiFePO4 cells managed by a BMS.
- PCS (Power Conversion System): the bidirectional inverter that converts DC battery power to AC grid/load (and back when charging).
- EMS (Energy Management System): the software that dispatches charge/discharge — peak shaving, TOU arbitrage, backup.
- Site controller & fire suppression: supervision, isolation and safety.
AC vs DC coupling
DC-coupled: PV feeds the battery through a DC-DC stage; efficient for solar+storage. AC-coupled: battery and PV each connect to the AC bus through their own inverters; simpler to retrofit.
How they talk
BMS reports cell data; PCS follows EMS setpoints; EMS talks to the site/cloud over Ethernet or cellular. In large systems the split of duties is exactly PCS vs BMS vs EMS.