RTE (Round-Trip Efficiency)

The ratio of energy discharged from a BESS to the energy required to charge it, expressed as a percentage. Can be measured at different levels — DC block, AC block, or complete plant at the Point of Connection (PoC) — with each level capturing different loss components (batteries, PCS, transformer, auxiliaries). IEC 62933-2-1 defines RTE at the PoC; typical values for lithium-ion BESS are 85–92% at rated power.