Start with the business objective
Sizing begins with the operating problem, not a cabinet model. Peak shaving, solar self-consumption, backup power and grid services each produce a different power-to-energy ratio. A system sized only from a monthly electricity bill can be too small to affect the target peak or unnecessarily large for the available charging window.
Define one primary use case and list secondary uses in priority order. This avoids a control strategy that tries to reserve the same battery capacity for several conflicting purposes.
Collect interval load data
Use at least 12 months of 15-minute interval data where possible. Mark production schedules, seasonal peaks, planned expansions, onsite solar and major loads that may start simultaneously. The highest recorded demand matters, but the shape and duration of each peak are more useful than one maximum value.
- Site import and export at each interval
- Electricity tariff and demand-charge rules
- PV generation and curtailment data
- Critical-load profile for backup operation
- Transformer and point-of-connection limits
Separate power from energy
Power, measured in kW, describes how fast the system must charge or discharge. Energy, measured in kWh, describes how long it can sustain that output. If a factory needs to reduce a 300 kW peak by 100 kW for two hours, the basic usable-energy requirement is 200 kWh before accounting for reserve, efficiency and degradation.
A practical design then checks charge opportunity, permitted depth of discharge, round-trip losses, temperature conditions and end-of-life capacity. The result may favor one larger cabinet, several modular cabinets or a containerized block.
Model the operating window
Simulate the proposed control logic against real load data. Confirm that the battery can recharge before the next event and that solar charging does not create a new grid peak. For backup requirements, separate energy reserved for resilience from energy available for daily cycling.
The usable operating window should also include a degradation allowance. A project expected to meet a contractual capacity late in its life should not be sized only to beginning-of-life nameplate energy.
Check the site constraints
Electrical and civil constraints can change the preferred architecture. Confirm available fault level, transformer rating, cable routes, fire separation, access for installation and maintenance, noise limits, ambient temperature, altitude and local permitting. A technically adequate battery can still be the wrong choice if it cannot be safely connected or serviced.
Prepare a useful supplier brief
A strong request for proposal includes the load file, single-line diagram, target operating strategy, site conditions, required standards and project schedule. Ask suppliers to state usable energy, continuous power, auxiliary consumption, environmental derating, warranty throughput and which items are included in the quoted scope.
Final sizing should be completed with the project engineer, utility requirements and a confirmed equipment specification. Early, structured data makes that process faster and produces proposals that can be compared on the same basis.