Solar Generator Watt Hours Explained: What It Really Means

Short answer: Watt hours (Wh) measures total energy capacity — how long a generator can run a device. A 1,000Wh generator running a 100W device lasts 10 hours (minus ~15% inverter losses). Most manufacturers list rated capacity; usable capacity is typically 80-90% of that number.

Rated vs Usable Capacity

A generator rated at 1,000Wh doesn’t deliver exactly 1,000Wh. Inverter losses (typically 10-15%), temperature effects, and battery management overhead reduce actual output. The EcoFlow DELTA 3 Max rated at 1,800Wh delivers approximately 1,530-1,620Wh in real-world use — about 85-90% efficiency.

How to Calculate Runtime

Runtime (hours) = (Usable Wh) ÷ (Device watts). For a 150W refrigerator on a 1,800Wh generator: 1,530Wh ÷ 150W = 10.2 hours. For a 40W CPAP over 8-hour nights: 1,530Wh ÷ 40W ÷ 8h = 47.8 nights.