BESS unit count calculator

Count whole BESS units for a power and energy need, then add fade to see how many you need later.

Read this first. Everything is at the AC terminals of the units, the basis of the Megapack 2 XL datasheet. The requirement, the 2% fade and the check year are placeholders, not sourced values. Fade is applied to energy only. Numbers use a dot for decimals; "10,000" is read as ten thousand.

Unit presets (Tesla Megapack 2 XL datasheet, Rev. 1.5.1, 10 February 2023):

Requirement (placeholders)

Power needed (MW) Hours at that power Fade (% of energy per year, placeholder) Must still deliver it at the start of year

One unit (AC basis)

Unit power (MW) Unit energy (MWh) AC round-trip efficiency (%)

Result

Item	Value
Unit duration (energy ÷ power)	-
Units to reach the power	-
Units to reach the energy when new	-
Units to reach the energy at the check year	-
Units to build	-
Built power and energy when new	-
First year the energy falls short	-
Charge needed for one full-requirement cycle, and loss	-

Method: units = the larger of the whole units for power, for energy when new and for energy at the check year. Energy at the start of year k is units × unit MWh × (1 − fade)^(k − 1). Charge for one cycle = energy delivered ÷ round-trip efficiency. Illustrative; not a design, a warranty or a guarantee. Check the manufacturer's data.