Energy, Solar & Electrical Sizing Guide

📚 Overview

Electrical calculations govern safety and power independence. Whether you are sizing a rooftop solar array, designing an RV battery storage bank, or calculating monthly air conditioning costs, understanding Watt's law and energy consumption is essential.

📐 Watt's Law & Kilowatt-Hour Electricity Cost

Monthly energy bill = Total kWh × Utility Rate per kWh. For solar: Daily Yield = System kW × Peak Sun Hours × 0.80 efficiency.

🔢 Worked Example

Scenario: Running a 1,500W space heater for 6 hours daily with electricity priced at $0.18 per kWh.

• Power: 1,500 Watts
• Daily Use: 6 hours
• Rate: $0.18/kWh

1. Daily watt-hours = 1,500 × 6 = 9,000 Wh = 9.0 kWh
2. Daily cost = 9.0 × $0.18 = $1.62
3. Monthly cost (30 days) = $1.62 × 30 = $48.60

💡 Pro Tips

• Never exceed 80% continuous electrical load on a standard circuit breaker (e.g. max 1,440W continuous on a 15A 120V circuit).
• Lead-acid batteries should only be discharged to 50% depth of discharge; Lithium iron phosphate (LiFePO4) can safely discharge to 80%–90%.
• Peak sun hours differ from daylight hours; they measure the equivalent hours of full 1,000 W/m² solar irradiance.
• Voltage drop in low-voltage 12V/24V systems requires substantially thicker copper wire gauge than 120V/240V circuits.

🧮 Energy Calculators (30)

Put the formulas above into practice with these free tools:

❓ Frequently Asked Questions