PV Toolbox

Five offline solar calculators. Estimate production, size strings and batteries, optimize your array, and calculate payback — free to download.

PV Toolbox puts five solar calculators in your pocket — everything you need to plan, size, and evaluate a solar system, completely offline.

No account. No subscription. No ads. Just the math.

FREE TOOLS

Solar Output Enter your system size, peak sun hours, and efficiency and get instant daily, monthly, and annual energy projections — plus a 25-year total with degradation factored in, and your CO₂ offset.

Payback Period Enter your system cost, incentives, electricity rate, and rate escalation and see your simple payback, break-even year, 25-year net savings, and ROI — with a 30-year cumulative savings chart.

PRO TOOLS — one-time purchase, unlocks all three forever

String Sizer Calculate safe series string lengths the right way: temperature- corrected Voc at your site's minimum temperature and Vmp at maximum, checked against your inverter's full voltage window. Know your exact safe range before you wire anything.

Battery Storage Size a battery bank for any combination of daily consumption, days of autonomy, depth of discharge, bank voltage, battery capacity, and round-trip efficiency. Supports lead-acid, LiFePO₄, and any other chemistry.

Array Optimizer Enter your panel specs and MPPT voltage range and get every possible series/parallel configuration ranked by harvest rate — with the array Vmp, Imp, and effective power at each operating point. Supports mixed panel groups with automatic mismatch loss calculation.

WHO IS THIS FOR?

If you're planning a rooftop system, building an off-grid cabin setup, sizing a van or RV solar install, or just working through the numbers before you buy anything — PV Toolbox has the calculations you need.

WORKS 100% OFFLINE

Every calculation runs on your device. No internet connection required, ever. Your data never leaves your phone.