Battery Bank Sizing: Why It Matters & How to Get It Right

Jun 13, 2025

A battery bank is a collection of batteries wired together to store energy from solar panels. This stored power ensures your devices and appliances keep running when sunlight isn’t available—whether at night or during cloudy weather.

Choosing the right battery bank size is crucial. If it's too small, you risk running out of power when you need it most. If it's too large, you waste money and space on unnecessary capacity. The key is to find a balanced setup that optimizes reliability, performance, and cost.

Step 1: Calculate Your Daily Power Consumption

Start by estimating your total daily energy usage.

  1. List all devices you plan to power.

  2. Note their wattage and how long you use them daily.

  3. Use an energy meter or check manufacturer specifications to get precise power consumption data.

Here’s an example of common appliance power usage:

Appliance Power (Watts) Hours/Day Daily Consumption (Wh)
LED Lights 40 5 200
Refrigerator 120 8 960
Laptop 60 4 240
TV 100 2 200
Total 1,600 Wh

Once you have your daily energy requirement, you can move on to battery sizing.

Step 2: Determine Your Required Battery Capacity

Use this formula to calculate the battery bank capacity in amp-hours (Ah):

Battery Bank Capacity (Ah) = (Total Daily Load in Wh × Days Without Recharge) ÷ (System Voltage × Depth of Discharge)

For example:

  • Daily load: 1,600 Wh

  • Days without recharge: 2

  • System voltage: 24V

  • Depth of discharge (DOD): 80% (0.8)

(1,600 × 2) ÷ (24 × 0.8) = 166.67 Ah

This means you need at least 166.67 amp-hours of usable capacity at 24 volts.

Step 3: Choose the Right System Voltage

Your system voltage affects efficiency and wiring requirements:

  • 12V: Best for small RVs or boats.

  • 24V: Ideal for mid-size solar setups.

  • 48V: Recommended for whole-home or commercial systems.

Higher voltages reduce current flow, allowing for thinner wires and better efficiency.

Step 4: Decide How Many Days of Backup You Need

Battery autonomy refers to how long your system can run without solar input.

  • 1 day: Cost-effective, minimal backup.

  • 2 days: Balanced, standard recommendation.

  • 3+ days: Ideal for critical applications or areas with limited sunlight.

Consider your location and energy needs when choosing autonomy.

Step 5: Select the Best Battery Type

Your battery choice impacts longevity and performance:

  • Lithium (LiFePO4): Long lifespan, fast charging, deep discharge, high efficiency.

  • AGM (Absorbed Glass Mat): Maintenance-free but fewer charge cycles.

  • Flooded Lead-Acid: Cheapest upfront but requires maintenance.

For solar users, lithium batteries offer the best long-term value.

Final Thoughts: Optimize Your Battery Bank for Maximum Efficiency

A properly sized battery bank ensures consistent power, cost savings, and long-term reliability. Whether you're powering an RV, off-grid home, or backup system, choosing the right setup will keep your energy flowing when you need it most.
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