Daily Wh = Σ (Appliance Wattage × Hours Used per Day)
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To build your own calculator or understand a downloaded template, you must use these fundamental formulas: Daily Wh = Σ (Appliance Wattage × Hours
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System kW = (Daily Wh / Peak Sun Hours) / 1000 .
Required Wh = Daily Consumption / System Efficiency (Standard efficiency is usually 0.7 to 0.8 to account for losses).
Panels = Required PV Array Power / Individual Panel Wattage . Free Solar Excel Templates for Download