Battery Round-Trip Efficiency (RTE)

Round-trip efficiency (RTE) measures the percentage of energy that a battery storage system can discharge relative to the energy it consumed during charging. In the context of utility-scale BESS, RTE is not a static number—it degrades over the lifespan of the project and fluctuates based on auxiliary loads (e.g., HVAC cooling systems, inverter losses, and step-up transformer inefficiencies). OPTIMUS models the nonlinear impact of ambient temperature and C-rate on RTE. Understanding real-world RTE is critical because every megawatt-hour lost to heat represents an immediate reduction in arbitrage margins, especially when charging from the grid during high-priced intervals.