Grid-Scale Battery Energy Storage Systems worked example

BESS Capacity Gap at 99% system availability: a worked example

Push system availability up to 99% and the picture changes. This example computes every intermediate figure at that operating point. Use it when validating that a BESS project configuration will meet the contracted MWh delivery requirement after accounting for system availability and round-trip efficiency losses.

The inputs for this scenario

  • Usable MWh per BESS container: 4 MWh / container (unchanged)
  • Number of BESS containers in the project: 50 containers (unchanged)
  • System availability: 99 % (raised for this scenario; the documented default is 95)
  • Round-trip efficiency: 87 % (unchanged)

Working through the calculation

  • Applying the documented formula (Gross BESS project capacity = usable MWh per container x number of BESS containers) to the inputs above produces each figure below.
  • At this operating point the engine returns 172 units for net deliverable bess mwh (availability and rte adjusted), the number this scenario is built around.
  • At this operating point the engine returns 200 units for gross bess project nameplate capacity (mwh).
  • At this operating point the engine returns 2 units for mwh lost to system availability deduction.
  • At this operating point the engine returns 25.74 units for mwh lost to round-trip efficiency losses.

How this compares with the baseline

  • Against the tool's baseline example, where system availability sits at 95% and the headline result is 165 units, this scenario comes in 4.21% above the baseline at 172 units.
  • It multiplies usable container energy by container count for gross nameplate, then derates by availability and round-trip efficiency to get net deliverable MWh. The value of this scenario is the size of the gap it exposes: that gap, priced out over a year, is the budget you can justify spending to close it.

Results at a glance

  • Net deliverable BESS MWh (availability and RTE adjusted): 172 units (headline result)
  • Gross BESS project nameplate capacity (MWh): 200 units
  • MWh lost to system availability deduction: 2 units
  • MWh lost to round-trip efficiency losses: 25.74 units

Run it with your numbers

  • Every input above is editable in the live BESS Capacity Gap calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.