Round-Trip Efficiency

Updated 2026-08-24 · Read this page as Markdown

The proportion of energy put into a battery system that comes back out again, after accounting for losses in charging, storage and discharging. A round-trip efficiency of 90% means ten kilowatt-hours in returns nine.

Compare figures carefully, because manufacturers measure round trip at different boundaries. A DC-to-DC figure covers only the cells and is flattering; an AC-to-AC figure includes the inverter's conversion losses in both directions and is what a household actually experiences. Standby consumption also matters: a system that idles at tens of watts around the clock quietly erodes the benefit of a small battery. Losses appear as heat, so poor round-trip efficiency and a hot-running installation tend to travel together, and both worsen at high charge and discharge rates.

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Related terms

AC Coupling A storage architecture in which the PV inverter and the battery inverter are separate units connected on the AC side. Solar energy is converted to AC first, and any surplus is then converted back to DC to charge the battery. Backup / Protected Loads Panel A separate distribution board containing the circuits that a hybrid or off-grid inverter will keep supplied during a grid outage. Only the loads wired into this board stay live when the utility supply fails. DC Coupling A storage architecture in which the PV array and the battery share the same DC bus inside a single hybrid inverter, so solar energy charges the battery without first being converted to AC. Only the energy actually consumed or exported passes through the DC-to-AC stage.

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