Battery packs smooth the aux-engine load profile - absorbing peaks, filling troughs - so gensets run closer to their best-SFOC operating point.
Formula
$$ \Delta F = \frac{(\text{SFOC}\text{peak} - \text{SFOC}\text{avg}) \cdot E_\text{batt}}{10^6 \cdot \eta_\text{RT}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\Delta F$ | Annual fuel saved | t | result |
| $\text{SFOC}_\text{peak}$ | Aux SFOC at peak load | g / kWh | NOx Technical File |
| $\text{SFOC}_\text{avg}$ | Aux SFOC at optimum (average) load | g / kWh | NOx Technical File |
| $E_\text{batt}$ | Annual kWh cycled through battery ($\text{capacity} \cdot \text{cycles} \cdot 365$) | kWh | operating profile |
| $\eta_\text{RT}$ | Battery round-trip efficiency | fraction | Li-ion 0.88–0.92 |
Peak-shaving requires accurate load forecasting - naive systems don’t cycle the battery enough to pay back. Full hybrid installations (battery + multiple gensets + power-management system) typically cut aux fuel 5–12 %.
Sources
- DNV - Battery systems for maritime applications.
- Corvus Energy - ESS white papers.
- IMO MSC.1/Circ.1645 - safety guidelines on lithium-ion batteries.