A BESS collects energy from renewable energy sources, such as wind and or solar panels or from the electricity network and stores the energy using battery storage technology. The batteries discharge to release energy when necessary, such as during peak demands, power outages, or grid balancing. In addition to the batteries, BESS requires additional components that allow the system to be connected to an electrical network.

A bidirectional inverter or power conversion system (PCS) is the main device that converts power between the DC battery terminals and the AC line voltage and allows for power to flow both ways to charge and discharge the battery. The other primary element of a BESS is an energy management system (EMS) to coordinate the control and operation of all components in the system.

BESS Power and Energy Ratings

For a battery energy storage system to be intelligently designed, both power in megawatt (MW) or kilowatt (kW) and energy in megawatt-hour (MWh) or kilowatt-hour (kWh) ratings need to be specified.

The power-to-energy ratio is normally higher in situations where a large amount of energy is required to be discharged within a short time period such as within frequency regulation applications. For pricing purposes, however, the quoted measure is usually the energy rating.

What is the Battery C‐Rate?

A battery’s C rating is the rate at which a battery can be fully charged or discharged. For example, charging at a C-rate of 1C means that the battery is charged from 0 - 100% or discharged from 100 - 0% in one hour.

A C-rate higher than 1C means a faster charge or discharge, for example, a 2C rate is twice as fast (30 minutes to full charge or discharge). Likewise, a lower C-rate means a slower charge or discharge, as an example, a C-rate of 0.25 would mean a 4-hour charge or discharge.