Thinking about solar + storage? One of the first and most important questions is: How much battery storage do you really need? Whether you’re trying to lower your energy bills, gain energy independence, or protect your business from outages, properly sizing your battery storage system is critical. The right setup can improve performance, increase ROI, and give you the power security you’re looking for—literally. In this article, we’ll walk you through how to determine your ideal battery size and what factors you should consider before investing.
Why Battery Size Matters
The size of your battery storage system determines how much energy you can store and use when solar isn’t available—at night, during peak demand times, or in power outages. Oversizing can be expensive, and undersizing can leave you without power when you need it most. Getting it right means greater efficiency, better ROI, and a more resilient energy solution.
Key Factors That Influence Battery Storage Size
1. Your Energy Usage
The first step is to evaluate your average daily energy consumption, typically measured in kilowatt-hours (kWh). This information can be found on your utility bill or by using a home energy monitoring system. Tip: Look at your peak usage times and monthly trends to get an accurate picture.
2. Backup Power Requirements
Do you want to power your entire home or facility, or just the essentials during an outage? Critical loads like refrigeration, medical devices, lighting, and Wi-Fi typically require less capacity than full-home backup systems.
3. Solar Panel System Size
The more solar energy you generate, the more you can store. If you’re already producing excess energy, adding the right amount of storage allows you to maximize your solar investment by using that energy when you need it most.
4. Your Goals: Savings vs. Resilience
Are you focused on cutting costs, avoiding peak demand charges, or ensuring 24/7 uptime? Your goals will influence your battery size and configuration. Commercial customers often prioritize demand shaving, while homeowners may focus on backup power and energy independence.
How to Calculate Battery Size: A Simple Formula
To get a rough estimate of your needed battery size, you can use this formula:
Battery Size (kWh) = Daily Energy Usage (kWh) × Days of Autonomy × Depth of Discharge / System Efficiency
Days of Autonomy: How many days you want backup power without sunlight (ex: 1–3 days)
Depth of Discharge (DoD): Most batteries can safely use 80-90% of their capacity
System Efficiency: Usually around 85–95% depending on the system
If you’re still unsure, Fortress Power’s team can walk you through a customized sizing assessment based on your actual usage and goals.
Why Choose Fortress Power for Your Energy Storage Needs?
Fortress Power offers scalable, high-performance lithium iron phosphate (LFP) battery solutions designed for both residential and commercial use. Our systems integrate seamlessly with new or existing solar setups, and they’re engineered for:
- Maximum storage capacity and longevity
- Smart energy management and real-time monitoring
- Reliable backup power for critical loads
- Fast installation and technical support
Whether you’re powering a home, warehouse, farm, or corporate campus, we help you right-size your system for optimized performance and long-term savings.
