How to Calculate & Measure Round-trip Efficiency of an Energy Storage System

Efficiency is the yardstick by which we measure how effectively a battery energy storage system (BESS) converts input energy into useful “work” or output. This concept is akin to evaluating the gas mileage of a car – it tells us how far we can go on a gallon of fuel. However, in the complex world of energy storage, efficiency is not a fixed value; it’s a dynamic metric influenced by various factors.

A BESS includes many components (each with its own efficiency) — power conversion, wires, cells, fuses, controls, etc. — and those subsystems (and how well they work together) have a cumulative effect on the efficiency of the overall system.

Given the number of parts to a typical grid-scale BESS, small losses throughout the system can add up to a much bigger overall total than one might guess. Efficiency improvements impact operating costs; just a one percent increase in efficiency can save a lot of money.

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