SolarSizer: Off-Grid PV Sizing

SolarSizer is an offline solar sizing calculator for off-grid and battery-based power systems — and it shows you the math behind every number. Built for installers, designers and serious DIY builders who need to check a design on site, without signal and without an account.

EVERY RESULT SHOWS ITS WORKING
Tap any result to see the formula used, the values that went in, the assumptions applied, and the standard or datasheet each constant came from. If a number cannot be defended, it should not be on your screen — so nothing hides behind a black box.

WHAT IT SIZES
• Load audit — build a daily energy profile from an appliance list with editable presets, and get simultaneous peak and surge power
• Solar panel array and string sizing — cold-morning maximum voltage, hot-cell minimum, and the valid string window for your controller or inverter
• Charge controller matching — MPPT and PWM, current, voltage window, array limits
• Battery bank — capacity for your days of autonomy, discharge-rate checks against the datasheet, and the reverse question: how long will this bank last?
• Inverter matching — continuous and surge, with headroom you set
• Conductors and protection — ampacity under real conditions, voltage drop, conductor size from your own drop target, and fuse or breaker selection
• Sizing engine: solar panel array and strings, battery autonomy, inverter matching, and conductor voltage drop.
• Every result shows its working — formula, inputs, assumptions, and the source of each constant (NEC 2023, IEC 60228).
• Offline PDF and plain-text reports, plus project backup.
• No ads. No account. No subscription. 100% offline.

WORKS THE WAY A JOB SITE WORKS
• Fully offline. No account, no sign-in, no ads, no analytics. Your projects stay on your device.
• One-time purchase. No subscription, no renewal, no upsell — you buy it once and it is yours.
• Metric and imperial, chosen per project
• High-contrast dark theme for outdoor use, large controls for gloved hands
• Save projects with named variants so you can compare options for the same site
• Export a client-ready PDF report and a plain-text summary, or back up your project files

HONEST BY DESIGN
SolarSizer performs engineering reference calculations. It is not a compliance certification and it does not replace design review. Default constants follow one named reference profile, every constant can be overridden, and each result shows exactly which values were used. Verify against the code edition your authority having jurisdiction has adopted before installing.

When a design cannot work — a string that exceeds your controller's cold-weather voltage limit, a bank that cannot deliver your surge, a conductor that fails ampacity or voltage drop — the app says so plainly and shows the fix, instead of quietly printing a number.

Off-grid solar sizing for installers, designers and DIY — buy once, no subscription, and every result shows its working.

Recent changes:
- Complete sizing engine: PV array, battery autonomy, string sizing, inverter matching, and conductor voltage drop.
- Transparent engineering audit working sheets with standard citations (NEC 2023 / IEC 60028).
- Offline PDF and plain-text report generation.
- Zero ads, no account required, 100% offline.