What Size Battery Energy Storage System Does Your Business Need?
Sep 16, 2026
Learn how to size a battery energy storage system for your business. Understand BESS power, energy capacity, load profile, peak shaving, solar integration, backup duration and battery sizing.
What Size Battery Energy Storage System Does Your Business Need?
For businesses considering battery energy storage, one of the first questions is often:
How large should the battery energy storage system be?
The answer is not simply based on the size of the solar system or the building's total electricity consumption.
A commercial or industrial Battery Energy Storage System (BESS) must be sized according to how the business intends to use the battery.
For example, a business may want BESS to:
Reduce peak electricity demand
Store excess solar energy
Increase solar self-consumption
Provide backup power
Shift energy consumption to lower-cost periods
Support microgrid operation
Improve energy resilience
Participate in applicable grid or energy-market programs
These applications can require very different battery configurations.
A 500 kWh battery may be suitable for one business but insufficient—or unnecessarily large—for another.
To determine the appropriate BESS size, businesses need to consider both power capacity and energy capacity, together with the site's load profile, solar generation, operating strategy and local electricity tariff.
1. What Does BESS Size Actually Mean?
One of the most common mistakes when discussing battery storage is treating battery size as a single number.
A BESS has at least two important capacity specifications:
Power Capacity
Power is normally measured in:
kW
MW
It describes how quickly the battery can charge or discharge electricity.
Energy Capacity
Energy is normally measured in:
kWh
MWh
It describes how much energy the battery can store.
For example:
500 kW / 1 MWh BESS
means approximately:
500 kW maximum power
1 MWh energy capacity
At a simplified level, 1 MWh of usable energy could provide 500 kW for approximately two hours.
This relationship can be expressed as:
Battery Duration = Energy Capacity ÷ Power Capacity
So:
1,000 kWh ÷ 500 kW = 2 hours
However, actual operating duration depends on factors such as usable state-of-charge range, efficiency, temperature, battery degradation and system operating limits.
2. Start With Your Business's Electricity Load Profile
Before choosing a battery, understand how your business consumes electricity.
The most useful information is not just your monthly electricity bill.
You should ideally have interval electricity data showing how your load changes throughout the day.
For example:
Time
Business Load
00:00–06:00
250 kW
06:00–09:00
400 kW
09:00–12:00
650 kW
12:00–15:00
800 kW
15:00–18:00
700 kW
18:00–22:00
450 kW
22:00–00:00
300 kW
This tells you much more than simply knowing that the facility uses, for example, 5,000 kWh per day.
Why?
Because BESS power requirements are closely related to the magnitude and duration of the loads you want the battery to address.
3. Decide What You Want the BESS to Do
The correct battery size depends heavily on the application.
This should be the first major design question:
What problem is the battery supposed to solve?
Different objectives lead to different sizing strategies.
Peak Shaving
If the main objective is reducing peak demand, the battery may need substantial power capacity but relatively short discharge duration.
Solar Energy Shifting
If the goal is storing daytime solar energy and using it later, energy capacity becomes particularly important.
Backup Power
If the battery must support critical loads during grid outages, both power and energy capacity must be calculated based on the critical loads and required backup duration.
Energy Price Arbitrage
If electricity prices vary during the day, the BESS can potentially charge during lower-cost periods and discharge during higher-cost periods, subject to local tariffs, regulations and system economics.
Solar Self-Consumption
A battery can store excess PV generation and discharge when solar production falls while the business continues to consume electricity.
These applications can also be combined.
4. How to Size BESS for Peak Shaving
Peak shaving is one of the most common commercial BESS applications.
Suppose a facility has:
Maximum demand: 1,000 kW
Desired grid demand: 700 kW
Peak period: 2 hours
The theoretical power reduction is:
1,000 kW − 700 kW = 300 kW
The theoretical energy requirement is:
300 kW × 2 hours = 600 kWh
So the preliminary requirement might be approximately:
300 kW / 600 kWh
But this is not necessarily the final BESS specification.
The actual system may need additional capacity because of:
Battery round-trip efficiency
Conversion losses
Reserve SOC
Maximum usable depth of discharge
Battery degradation
Temperature
Power conversion system limits
Therefore, the final design should be based on the actual operating model rather than the simple theoretical calculation alone.
5. How to Size BESS for Solar Energy Storage
Solar + BESS is another major commercial application.
Imagine a factory has:
1 MW of solar PV
During the middle of the day, solar generation exceeds the facility's immediate consumption.
Instead of exporting all excess solar electricity, the system can potentially charge the battery.
Later, when solar production decreases, the battery can discharge.
A simplified energy flow could look like:
Solar PV → Business Load
and when solar generation exceeds demand:
Solar PV → BESS
Later:
BESS → Business Load
This can increase the amount of solar energy used on-site, depending on the site's operating conditions and applicable grid rules.
6. Solar PV Size Does Not Automatically Determine Battery Size
A common misconception is:
“If I have a 1 MW solar system, I need a 1 MWh battery.”
Not necessarily.
The appropriate BESS size depends on:
How much excess solar energy is generated
When excess generation occurs
How much energy the business consumes
How long the battery should discharge
Grid export limitations
Desired operating strategy
Battery power rating
For example, two facilities can both have:
1 MW PV
but have very different load profiles.
Factory A
Most electricity is consumed during the daytime.There may be relatively little excess solar energy to store.
Factory B
Electricity demand is lower during the day but remains high into the evening.A larger battery may provide more opportunities for solar energy shifting.
Therefore:
Same PV capacity ≠ Same BESS requirement
7. Power Capacity vs. Energy Capacity
This distinction is critical when sizing BESS.
Consider two systems:
System A
500 kW / 500 kWh
System B
500 kW / 2 MWh
Both can potentially discharge at 500 kW.
But their approximate theoretical durations are:
System A: 1 hour
System B: 4 hours
This means businesses should ask two separate questions:
Question 1:
How much power do I need?Measured in kW or MW.
Question 2:
How long do I need that power?
Measured in hours.
Together, these determine the required energy capacity.
8. How Much BESS Do You Need for Backup Power?
Backup sizing is different from peak shaving.
You first need to identify the critical loads that must remain operational during a grid outage.
For example:
Critical Load
Power
Emergency lighting
20 kW
IT equipment
30 kW
Cooling system
100 kW
Production equipment
200 kW
Security systems
10 kW
Total
360 kW
If the business requires four hours of backup:
360 kW × 4 hours = 1,440 kWh
A preliminary calculation therefore gives:
360 kW / 1.44 MWh
The final BESS would need to account for usable energy, system efficiency, operating reserve and battery aging.
9. Not Every Load Needs to Be Backed Up
One way to reduce BESS requirements is to distinguish between:
Critical loads
and
Non-critical loads
For example, during a grid outage, a factory may prioritize:
IT systems
Emergency lighting
Security
Communications
Essential refrigeration
Selected production equipment
while temporarily disconnecting:
Non-essential HVAC
EV charging
Non-critical machinery
Other flexible loads
This approach can significantly change the required battery power and energy capacity.
Therefore, a good BESS design should consider load prioritization and energy management, not just total facility capacity.
10. How Does Battery Depth of Discharge Affect Sizing?
Battery specifications may distinguish between nominal capacity and usable capacity.
For example, suppose a battery system has:
1,000 kWh nominal capacity
but the system is designed around an 90% usable energy window.
The usable energy would be approximately:
1,000 kWh × 90% = 900 kWh
Other system losses may further reduce the energy available to the load.
This is why businesses should look at usable energy capacity under the intended operating conditions, rather than comparing nominal MWh figures alone.
11. Battery Degradation Should Be Considered
Battery capacity changes over time.
A BESS sizing study should therefore consider the expected operating life and degradation characteristics of the selected battery system.
For example, if a project requires a certain amount of usable energy throughout its operating life, the initial system may need to provide sufficient capacity to account for expected degradation.
The exact approach depends on:
Battery chemistry
Cell design
Operating temperature
Charge/discharge rate
Cycling frequency
Depth of discharge
Manufacturer warranty
Energy management strategy
For this reason, battery sizing should be evaluated using the manufacturer's technical documentation and warranty conditions.
12. What Battery Chemistry Should a Business Use?
Modern commercial BESS projects commonly use lithium-ion battery technologies, with LFP (lithium iron phosphate) widely used for stationary energy storage.
However, battery chemistry is only one part of system selection.
Businesses should also evaluate:
Usable energy
Power rating
Cycle capability
Operating temperature
Safety architecture
Thermal management
Battery management system
Warranty
Container or cabinet configuration
Fire protection
Certification and compliance
Service and maintenance requirements
The right battery should be evaluated as part of the complete BESS rather than solely by cell chemistry.
13. How Large Should a Commercial BESS Be?
There is no universal BESS size for commercial buildings.
Commercial systems can range from relatively small installations to multi-megawatt, multi-megawatt-hour systems.
A preliminary sizing process can be:
Step 1: Determine the application
Peak shaving?Solar shifting?Backup?Arbitrage?Or a combination?
Step 2: Analyze the load
Identify:
Peak demand
Average demand
Critical loads
Load duration
Daily and seasonal patterns
Step 3: Analyze solar production
If PV is installed, determine:
PV capacity
Hourly generation
Excess solar
Export limitations
Step 4: Calculate required battery power
Determine the maximum charge/discharge power required.
Step 5: Calculate required energy
Estimate:
Required Energy = Required Power × Required Duration
Then adjust for efficiency, usable SOC range, reserve requirements and degradation.
Step 6: Simulate the system
For larger projects, hourly or sub-hourly modeling can compare different BESS configurations and operating strategies.
14. Example: Sizing a BESS for a Manufacturing Facility
Consider a hypothetical manufacturing facility with:
Peak load: 1,500 kW
Average daytime load: 1,000 kW
Solar PV: 1,000 kW
Desired peak reduction: 300 kW
Required peak-shaving period: 3 hours
The basic energy requirement would be:
300 kW × 3 hours = 900 kWh
This suggests a preliminary requirement around:
300 kW / 900 kWh
But the final system could require a larger nominal energy capacity after considering usable SOC, efficiency, reserve capacity and degradation.
If the business also wants several hours of backup power, the BESS may need to be significantly larger.
This example illustrates why:
BESS sizing should be based on the intended operating strategy, not simply the size of the solar installation.
15. How Long Should a Commercial Battery Last?
The required discharge duration depends on the application.
A short-duration BESS may be designed around:
Peak demand management
Power quality
Short-term load support
A longer-duration system may be designed for:
Solar energy shifting
Extended backup
Longer energy arbitrage periods
For example:
Application
Main Sizing Consideration
Peak shaving
Power + peak duration
Solar shifting
Excess solar energy + discharge period
Backup
Critical load + backup duration
Arbitrage
Price periods + energy capacity
Microgrid
Load + generation + operating strategy
The correct duration should therefore come from the business case.
16. Should You Oversize a BESS?
Oversizing a battery is not automatically beneficial.
A larger battery can provide:
More stored energy
Longer discharge duration
Greater flexibility
Additional future operating options
But it can also increase:
Initial investment
Space requirements
HVAC and auxiliary consumption
Installation complexity
Maintenance requirements
The goal should be to find the BESS configuration that meets the business's operational requirements and project economics.
17. BESS Sizing Should Include the Inverter or PCS
A battery system is not just a collection of battery cells.
Commercial BESS typically includes components such as:
Battery modules/racks
Battery Management System (BMS)
Power Conversion System (PCS)
Energy Management System (EMS)
Thermal management
Fire protection
Protection and switching equipment
Monitoring and communications
The PCS power rating determines how quickly energy can generally move between the battery and the AC system.
For example:
1 MW / 2 MWh BESS
has a nominal two-hour energy-to-power relationship.
But if the project requires 2 MW of discharge power for short periods, a 1 MW PCS would not meet that requirement even though the battery may contain 2 MWh of stored energy.
This is why BESS sizing must consider both battery energy capacity and power conversion capacity.
18. Solar + Inverter + BESS: Design the System Together
For businesses installing both solar and storage, it is better to evaluate the system as an integrated energy solution.
A typical architecture may look like:
Solar Panels → Solar Inverter → AC Bus → Business Loads
with:
Battery ↔ PCS ↔ AC Bus
An alternative architecture may use DC coupling depending on the equipment and project design.
The appropriate architecture depends on:
Existing PV system
New PV system
Battery size
Inverter architecture
Grid connection
Retrofit requirements
Operating strategy
For commercial projects, integrating solar panels, inverters and BESS during the design stage can help create a more coordinated energy management strategy.
19. What Information Does an EPC Need to Size Your BESS?
If you are requesting a BESS proposal from an EPC, integrator or supplier, prepare as much of the following information as possible:
Electrical Information
Site voltage
Grid connection capacity
Maximum demand
Average demand
Load profile
Critical load requirements
Solar Information
PV capacity
Module type
Inverter capacity
Hourly or daily PV generation
Existing or planned PV system
Business Requirements
Peak shaving target
Backup duration
Solar self-consumption target
Operating schedule
Expected annual cycles
Future expansion plans
Site Information
Available installation area
Indoor or outdoor installation
Ambient temperature
Environmental conditions
Fire protection requirements
With this information, a BESS provider can develop a much more meaningful technical proposal.
20. BESS Sizing Checklist for Businesses
Before selecting a battery energy storage system, ask:
Power
What is the maximum power the BESS must deliver?
What is the required charging power?
What is the maximum site demand?
Energy
How many kWh or MWh need to be stored?
How long should the battery discharge?
How much usable energy is required?
Solar
How large is the PV system?
How much excess solar energy is available?
Are there grid export limitations?
Backup
Which loads are critical?
How many hours of backup are required?
Are there starting currents from motors or other equipment?
Battery
What battery chemistry is being used?
What is the usable SOC range?
What are the degradation assumptions?
What is the warranty?
System
What PCS power rating is required?
What EMS functions are needed?
What safety and thermal management systems are included?
Does the system comply with applicable local requirements?
Frequently Asked Questions
1. How do I calculate the size of a battery energy storage system?
A basic calculation is:
Energy Capacity = Required Power × Required Discharge Duration
However, the final BESS size should also account for usable SOC range, system efficiency, reserve capacity, battery degradation and operating conditions.
2. What size BESS do I need for a 1 MW solar system?
A 1 MW solar system does not automatically require a 1 MWh BESS. The appropriate battery size depends on excess solar generation, load profile, desired discharge duration, power requirements and the project's operating strategy.
3. What is the difference between MW and MWh in BESS?
MW describes power—the rate at which electricity can be delivered or absorbed.MWh describes energy—the amount of electricity that can be stored.
For example, a 1 MW / 2 MWh system has a nominal two-hour energy-to-power relationship.
4. How much BESS do I need for peak shaving?
Start by determining how much grid demand you want to reduce and how long the reduction must be maintained.
A simplified calculation is:
BESS Power = Peak Demand − Target Demand
BESS Energy = BESS Power × Required Duration
The final design must then account for system losses, usable energy and operating reserves.
5. Can I add BESS to an existing solar system?
Yes, BESS can potentially be integrated with an existing PV installation. The appropriate architecture depends on the existing solar inverter, grid connection, battery system, PCS and desired operating strategy.
6. How many hours of battery storage does a business need?
There is no universal requirement. Peak-shaving applications may prioritize power over long duration, while solar shifting and backup applications may require greater energy capacity.
7. Is a larger commercial battery always better?
No. A larger BESS provides more energy capacity but also increases capital cost, space requirements and system complexity. The appropriate size should be determined by the business's load profile, energy objectives and project economics.
8. Can BESS work with solar panels and a solar inverter?
Yes. Solar PV, inverters and BESS can be integrated into a coordinated energy system. The architecture can be AC-coupled, DC-coupled or another configuration depending on the equipment and project requirements.
Conclusion
So, what size battery energy storage system does your business need?
The answer starts with two numbers:
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