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Power budget · size the battery and panel

This bench runs the sizing arithmetic of the 12 V power build on your own numbers. Enter the current you measured, the daily run time, and the amp-hour rating of the battery you found. It returns daily energy in watt-hours, usable capacity at the depth of discharge your chemistry allows, days of storage, and the array wattage that replaces one day of energy.

Daily energy

105 Wh

Days of storage

5.7

Array wattage

30 W

Start from a worked example

Measured current 0.7 A

Daily run time 10 h

Battery amp-hour rating 100 Ah

Battery chemistry

Peak sun hours 5 h

Terms and figures. “Peak sun hours”, “days of storage” and “depth of discharge” are the terms used in the Study Guide for Photovoltaic System Installers (NABCEP, v3, August 2005; prepared for the U.S. Department of Energy and Sandia National Laboratories), which states: “suppose the batteries provide two days of storage with no more than an 80% depth of discharge.” “Amp hour rating” for a battery’s labelled capacity follows Micah Toll, DIY Lithium Batteries. Not sourced: the 50% depth-of-discharge limit for lead-acid and the 1.25 design margin are bench conventions used here, not figures traced to a reference. Size to your own battery’s datasheet.