How to Size a Battery Energy Storage System (BESS): A Comprehensive Guide

Sizing a Battery Energy Storage System (BESS) correctly is essential for maximizing energy efficiency, ensuring reliable backup power, and achieving cost savings. Whether for a commercial, industrial, or residential setting, properly sizing a BESS allows users to store and utilize energy in a way that meets their specific needs. At EverExceed, we specialize in customized energy storage solutions that fit the unique requirements of each customer. In this guide, we’ll walk you through the key factors to consider when sizing a battery energy storage system.

Why Proper Sizing is Important

A well-sized BESS ensures you have adequate energy to meet demand, avoid excessive costs, and support sustainability goals. Proper sizing can help:

Ensure Energy Availability: A BESS sized to your needs will provide sufficient power during peak demand or outages.

Optimize System Efficiency: Oversizing can lead to unnecessary expenses, while undersizing may not meet your energy requirements.

Maximize Cost Savings: A well-sized system aligns with your power consumption and financial goals, helping you avoid over-investment while maximizing returns.

Key Steps in Sizing a Battery Energy Storage System

To accurately size a BESS, consider factors like energy needs, power requirements, and intended applications. Here’s a breakdown of each step.

1. Determine Your Energy Requirements (kWh)

Understanding your total energy needs, measured in kilowatt-hours (kWh), is the foundation for sizing a BESS. Energy requirements depend on how much power you need and for how long. Start by evaluating:

Daily Energy Consumption: Calculate your total energy use over a 24-hour period. For commercial setups, review electricity bills or use monitoring devices to track energy usage.

Backup Duration Needs: If the BESS is for backup, determine how many hours or days you want it to last during an outage.

Formula:
Energy Storage Capacity (kWh) = Average Power Demand (kW) x Desired Duration of Backup (hours)

For example, if your average demand is 5 kW and you need backup for 10 hours, your required storage capacity would be 5 kW x 10 hours = 50 kWh.

2. Consider Peak Power Demand (kW)

The peak power requirement, measured in kilowatts (kW), indicates the maximum power your BESS needs to provide at any given moment. This is crucial for applications where high power is needed in short bursts.

Determine Peak Load Requirements: Analyze the maximum power your system needs to handle during peak times. This may be significantly higher than your average load.

Account for Instantaneous Demand: Some systems, especially industrial setups, experience short, high-power demands. Make sure your BESS can handle these peaks without overloading.

For example, if you experience peak demands of 20 kW for short periods, ensure your BESS inverter or power electronics can support this.

3. Define the Depth of Discharge (DoD) and Battery Type

The depth of discharge (DoD) defines how much of the battery's capacity can be used without compromising its lifespan. Different battery chemistries allow for different DoDs, which affects the usable capacity of the BESS.

Lithium-Ion Batteries: Typically offer a DoD of 80-90%, allowing for a high utilization rate without damaging the battery.

Lead-Acid Batteries: Have a lower DoD, around 50%, meaning you can only use half of the rated capacity to maintain battery life.

Formula:
Usable Capacity (kWh) = Total Capacity (kWh) x Depth of Discharge (%)

For example, if you have a 100 kWh lithium-ion battery with a DoD of 90%, the usable capacity would be 100 kWh x 0.9 = 90 kWh.

4. Evaluate the Charging and Discharging Rate

Charging and discharging rates affect how quickly the battery can be charged or used. This is especially important if you need rapid energy storage or quick discharge for high power applications.

Charge Rate (C-Rate): The C-rate determines how quickly a battery can be charged. A 1C rate means the battery charges in 1 hour, while a 0.5C rate means it takes 2 hours.

Discharge Rate: This rate depends on how quickly you need to draw power. Higher discharge rates are typically required for systems with high power demand.

For instance, if you need to recharge a 50 kWh system in 2 hours, you’d require a 0.5C charge rate.

5. Account for Efficiency Losses

No battery system is 100% efficient. Losses can occur during charging and discharging due to heat and other factors, typically reducing efficiency to 85-95%.

Round-Trip Efficiency: The percentage of energy retained after a full charge-discharge cycle. Higher round-trip efficiency means less energy is lost.

Formula:
Effective Capacity (kWh) = Usable Capacity (kWh) x Round-Trip Efficiency (%)

For example, if you have a usable capacity of 90 kWh with an efficiency of 90%, the effective capacity would be 90 kWh x 0.9 = 81 kWh.

6. Decide on the System’s Primary Use Case

Consider what the primary function of the BESS will be:

Peak Shaving: Sizing for peak shaving requires a BESS that meets peak demands without drawing from the grid.

Backup Power: For emergency backup, size the BESS to cover critical loads for the desired duration.

Load Shifting: To store energy during off-peak times and use it during peak periods, size the BESS based on daily consumption patterns.

Knowing the primary use case helps narrow down capacity and power needs, ensuring the system is optimized for its intended function.

7. Consider Future Scalability

If your energy needs are likely to grow, choose a system that allows for easy expansion. A modular BESS enables additional batteries to be added over time, providing flexibility and accommodating increased demand without a complete system overhaul.

Sizing Example: Commercial Battery Storage System

Let’s walk through a sizing example for a commercial BESS designed for backup power:

Daily Consumption: 100 kWh

Backup Duration Required: 8 hours

Depth of Discharge (DoD): 90%

Round-Trip Efficiency: 90%

Energy Storage Capacity Required: 100 kWh (daily consumption) x 8 hours (duration) = 800 kWh

Total Battery Capacity (accounting for DoD): 800 kWh / 0.9 (DoD) = ~889 kWh

Effective Capacity (accounting for efficiency): 800 kWh x 0.9 (efficiency) = 720 kWh

In this case, a BESS with an approximate capacity of 889 kWh would meet the business’s needs effectively.

Why Choose EverExceed for Your Battery Energy Storage Solution

At EverExceed, we provide expertly designed battery energy storage solutions that are customized to fit your specific needs. Our BESS systems are crafted with high-performance lithium-ion technology, advanced energy management software, and modular designs for scalable solutions.

Customized Sizing: We work with you to accurately size the BESS to meet your power and energy requirements.

Advanced Management Systems: Our systems include sophisticated monitoring tools that optimize energy usage and extend battery life.

Reliable and Efficient: With high-efficiency batteries and smart control systems, our solutions ensure maximum performance and reliability.

Conclusion: Get the Right BESS for Your Needs

Sizing a battery energy storage system is a critical step in achieving energy independence, cost savings, and backup power. By considering your energy requirements, peak power demand, battery type, efficiency, and future scalability, you can select a BESS that will support your goals effectively.

At EverExceed, we’re here to help you through every step of the process, ensuring you receive a BESS that fits your unique needs. Contact us today to discuss how our energy storage solutions can empower your business.