Calculate daily household electrical energy consumption (Watt-hours / kWh) and peak surge load for off-grid solar system sizing.
ℹ️ Note: Load profiles must itemize seasonal runtime changes (heating/cooling cycles) to maintain reliable year-round operation.
The Solar Load Calculator is the indispensable first step in designing any independent off-grid solar energy system.
To build a system that never runs out of power, you must accurately calculate two distinct figures: Total Daily Energy (Kilowatt-Hours per day, which dictates solar panel and battery size) and Maximum Simultaneous Power (Continuous and Surge Watts, which dictates inverter capacity).
Our tool breaks down continuous loads, cyclical compressor loads (refrigerators and air conditioners), and standby phantom loads, giving you an exact mathematical baseline for system engineering.
A homeowner working remotely runs high-efficiency appliances with Starlink satellite internet and an Energy Star refrigerator.
150W Running × 8 Hours Compressor Run Time = 1,200 Wh/day
Refrigerators do not run continuously; their compressors cycle on and off for roughly 8 hours out of 24.
(50W Starlink × 24 hrs) + (65W Laptop × 6 hrs) = 1,200 Wh + 390 Wh = 1,590 Wh/day
Always-on telecommunications draw significant cumulative energy despite modest instantaneous wattage.
(4x 10W LEDs × 5 hrs) + (2x 15W Phones × 2 hrs) = 200 Wh + 60 Wh = 260 Wh/day
Total Daily Load = 1,200 + 1,590 + 260 = 3,050 Wh (3.05 kWh/day).
✅ Engineering Sizing Result: Total daily energy consumption is 3.05 kWh/day with a 1,200W starting surge, establishing the foundation for all subsequent sizing.
Computes total energy utilized over a standard 24-hour cycle for each appliance.
Converts aggregate Watt-hours into standard billing and sizing Kilowatt-hours.
| Appliance | Running Watts | Daily Hours | Daily Energy (Wh) | Surge Watts |
|---|---|---|---|---|
| Energy Star Refrigerator | 120W – 180W | 8 hrs (Duty Cycle) | 1,200 Wh | 1,200W – 1,500W |
| Starlink Satellite Dish | 45W – 65W | 24 hrs | 1,300 Wh | 75W |
| LED Lighting (4 Fixtures) | 40W | 5 hrs | 200 Wh | 40W |
| Laptop Computer & Monitor | 85W | 8 hrs | 680 Wh | 100W |
| Microwave Oven | 1,100W | 0.3 hrs (20 mins) | 360 Wh | 1,500W |
| Coffee Maker | 900W | 0.2 hrs (12 mins) | 180 Wh | 900W |
Check the UL electrical rating label on the back or bottom of the appliance. If it lists Volts and Amps instead of Watts, multiply Volts by Amps (Watts = Volts × Amps). Alternatively, plug the appliance into a Kill-A-Watt electricity meter for 24 hours.
Phantom load is electrical power consumed by electronics (TVs, microwaves, chargers, stereo systems) while turned off or in standby mode. In an off-grid home, phantom loads can easily waste 500 Wh to 1,000 Wh per day unless isolated on switched power strips.
Electric resistance heating (stoves, water heaters, space heaters) consumes massive amounts of power (1,500W to 4,000W continuous). Most off-grid homes use propane or wood for cooking and heating to keep solar array and battery bank costs manageable.
Calculate array size in Watts to supply your calculated daily kWh.
Next StepStore enough energy for nights and cloudy weather.
Next StepHandle continuous running watts and inductive motor surges.
