Measurement
Round-trip efficiency is a measure of energy storage system performance, indicating the percentage of energy put into storage that can be retrieved for use later. It considers all losses during the charging and discharging process. For example, if you use 100 kWh to charge a battery and later get 80 kWh back out, the system’s round-trip efficiency is 80%. High round-trip efficiency means minimal energy loss in storage (common values for lithium-ion batteries are around 85-95%). This metric is important for evaluating storage technologies (batteries, pumped hydro, etc.) because it affects the overall economics and effectiveness of storing renewable energy for later use.