How much battery storage does a commercial or industrial facility need?
BESS sizing depends on the facility’s load profile, peak demand, energy consumption, operating hours, and the purpose of the system.
A properly sized Battery Energy Storage System (BESS) should provide enough power for the required load while maintaining sufficient energy capacity for the intended operating duration. Oversizing increases project cost, while undersizing can limit savings and system performance.
This guide explains the key factors used to size a C&I BESS.
What Determines BESS Size?
BESS sizing has two primary parameters:
- Power capacity (kW / MW) – how much power the battery can deliver or absorb at one time.
- Energy capacity (kWh / MWh) – how much energy the battery can store.
For example, a 500 kW / 1 MWh BESS can theoretically deliver 500 kW for approximately two hours under ideal conditions.
The correct ratio between power and energy depends on the application.
1. Start With the Facility Load Profile
The first step is to understand how the facility consumes electricity.
Key data includes:
- Average power demand
- Maximum demand
- Daily and monthly energy consumption
- Peak-demand periods
- Operating hours
- Seasonal load variations
- Existing solar generation, if applicable
A 24-hour manufacturing facility may require a very different BESS from a warehouse operating mainly during daytime hours.
For accurate sizing, 15-minute or 30-minute interval load data is generally more useful than monthly electricity consumption alone.
2. Define the BESS Application
The required battery size depends heavily on what the system is designed to achieve.
Peak Shaving
For demand-charge reduction, the BESS discharges during periods of high power demand.
A simplified calculation is:
Required BESS Power ≈ Peak Demand − Target Grid Demand
For example, if a facility reaches a 1.5 MW peak and the target grid demand is 1.0 MW, approximately 500 kW of discharge power is required.
The required energy capacity then depends on how long the peak lasts.
Solar Energy Time Shifting
When BESS is paired with solar PV, the battery can store excess daytime generation and discharge it later.
In this case, sizing should consider:
PV surplus → BESS charging → evening or peak-period discharge
The battery should be large enough to capture useful surplus energy without creating unnecessary capacity.
Backup and Energy Resilience
For backup applications, sizing depends on:
- Critical load
- Required backup duration
- Load priority
- Maximum backup power
For example, if critical loads require 300 kW for two hours:
300 kW × 2 hours = 600 kWh
A system larger than 600 kWh may then be required after accounting for usable capacity, reserve margin, efficiency and battery operating limits.
3. Determine the Required Energy Capacity
A simple starting formula is:
BESS Energy Capacity (kWh) = Required Power (kW) × Discharge Duration (hours)
For example:
500 kW × 2 hours = 1,000 kWh
This gives a basic requirement of 500 kW / 1 MWh.
However, the final battery capacity should also consider:
- Depth of Discharge (DoD)
- Round-trip efficiency
- Temperature
- Battery degradation
- Reserve capacity
- Project operating strategy
Therefore, the installed capacity is normally higher than the simple usable-energy calculation.
4. Match the PCS With the Battery
The Power Conversion System (PCS) determines how much power the BESS can charge or discharge.
The PCS rating should be selected according to:
- Maximum charging power
- Maximum discharging power
- Grid requirements
- Load profile
- Battery configuration
- Operating strategy
A 1 MWh battery does not automatically require a 1 MW PCS.
For example:
1 MW / 2 MWh → approximately 2-hour system
1 MW / 4 MWh → approximately 4-hour system
The appropriate configuration depends on the project objective rather than battery capacity alone.
5. Consider Solar PV and EV Charging Loads
For integrated energy projects, BESS should not be sized independently.
When a site combines solar PV, BESS and EV charging, the system should consider:
Solar Generation → BESS → EV Charging → Facility Load → Grid
High-power DC charging can create short-duration demand peaks. A BESS can help manage these peaks and reduce the required grid capacity in some applications.
Similarly, solar generation can be used to charge the battery when excess PV power is available.
Example: C&I BESS Sizing
Consider a manufacturing facility with:
- Maximum demand: 2 MW
- Target grid demand: 1.5 MW
- Peak duration: 2 hours
Required peak-shaving power:
2 MW − 1.5 MW = 500 kW
Basic energy requirement:
500 kW × 2 hours = 1 MWh
A preliminary solution could therefore be around:
500 kW / 1 MWh BESS
The final design would then adjust the battery capacity and PCS rating based on DoD, efficiency, degradation, reserve requirements, site conditions and the actual load profile.
What Is the Right BESS Size for Your Project?
There is no universal BESS size for commercial and industrial applications.
A practical sizing process is:
Load Analysis → Application Definition → Power Requirement → Energy Requirement → PCS Selection → Battery Configuration → EMS Strategy
For larger projects, the design should also consider MV transformers, switchgear, protection systems, grid connection requirements and site electrical infrastructure.
The objective is not simply to install the largest possible battery. The goal is to select the right power and energy capacity for the project’s technical and economic requirements.
Need Help With C&I BESS Sizing?
Splendor Energy provides integrated BESS, solar PV, PCS, EMS and electrical infrastructure solutions for commercial and industrial energy projects.
From initial load analysis to system configuration and equipment supply, we can help develop a BESS architecture based on your site’s operating requirements.
Contact Splendor Energy to discuss your C&I BESS project.
