Power and energy are different
Power in kilowatts (kW) describes the simultaneous load a system can supply. Energy in kilowatt-hours (kWh) describes how much energy can be delivered over time. Both parameters must be selected.
A simple illustrative calculation
A constant 10 kW load for 2 hours needs 20 kWh delivered to the load: E = P × t. This illustrates the arithmetic and is not a finished specification. Nominal battery capacity must also account for losses, allowable depth of discharge, temperature and ageing.
What changes the result
Starting currents, brief peaks, load profile, PCS limits, BMS operation and the required emergency reserve all matter. Motors and sensitive processes also require attention to transient behaviour.
What your engineer needs
An hourly or more detailed load profile, a list of critical circuits, connection parameters and details of existing solar or a generator. Payback depends on actual tariffs, operating modes and site conditions; there is no universal figure.
Further reading
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