How much battery, how much solar, and what wire.

Every van build thread ends the same way: 200 Ah, 400 W, and a fridge that dies in November. The numbers are not hard, they are just several, and the month matters more than the panel.

WHAT IT DOES

• Loads to watt-hours a day, with AC loads through the inverter's efficiency and its idle draw counted
• Battery bank for your days of autonomy: LiFePO4, AGM or flooded, 12, 24 or 48 V, with the nearest build in 100 Ah units
• Solar by month and latitude band, flat roof or tilted, with a system derate; alternator charging from DC-DC amps and driving hours
• Solar watts needed for the design month, with and without driving; recharge time from a flat bank
• Month-by-month chart of production against use; shortfall months named with three fixes sized
• Inverter size from the AC peak
• Wire gauge (14 AWG to 4/0) for every run from voltage drop and ampacity, actual drop, and the fuse size
• Printable build sheet

Who it's for

Van, bus, boat and cabin builds; anyone sizing an off-grid system before buying the parts.

What you get

• The sizer (one .html file, runs in any browser, offline)
• A 2-page quick-start guide

Good to know

• One file. No install, no account, no subscription, no internet needed after download.
• Your data stays on your computer. Export a backup any time; import it on another machine.
• Works on Mac, Windows, Linux and iPad (open the file in Safari or Chrome).
• Instant download.

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