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Energy, Solar & Electrical Sizing Guide

Solar panel generation, battery amp-hours, appliance kilowatt-hours, and wiring load.

30 free calculatorsFormula includedWorked example

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📚 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

Power (Watts) = Voltage (V) × Current (Amps) and kWh = (Watts × Hours) / 1000

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

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

Operating the heater costs $1.62 per day or $48.60 each month.

💡 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:

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