How to Calculate Solar Power Needs: A Practical 5-Step Guide

1. Determine Your Energy Consumption

First, calculate total daily watt-hour (Wh) requirements using this formula:

• Total Load (W) × Daily Usage Hours = Daily Energy Consumption

Example: Two 50W lights operating 8 hours daily
50W × 2 × 8h = 800Wh

2. Battery Bank Sizing

Account for consecutive cloudy days and depth of discharge (DoD):

• Battery Capacity (Ah) = (Daily Wh ÷ System Voltage) × (Backup Days + 1) ÷ DoD

For 12V system needing 5-day backup with 50% DoD:
(4,000Wh ÷ 12V) × 6 ÷ 0.5 = 4,000Ah

Depth of Discharge Guidelines

• Lead-Acid: 50% maximum
• LiFePO4: 80% maximum

3. Solar Panel Calculation

Factor in local sunlight hours and system losses (typically 20-30%):

• Panel Wattage = Daily Wh ÷ Sun Hours ÷ 0.7

In regions with 4 peak sun hours:
4,000Wh ÷ 4h ÷ 0.7 = 1,428W required

4. System Voltage Selection

Choose based on total load:

• 12V: <1,500W systems
• 24V: 1,500-3,000W
• 48V: >3,000W

5. Real-World Adjustment Factors

• Add 25% margin for panel degradation
• Consider temperature derating (up to 20% loss)
• Account for wiring efficiency (97-99% per connection)

Quick Reference Chart

Remember: These calculations assume 4 peak sun hours. For precise results, use satellite irradiation data from tools like NASA POWER or PVWatts. Always consult certified installers for grid-tied systems requiring utility interconnection approval.