About OffroadWatt

OffroadWatt is a free, independent tool that helps you size and understand the electrical system of a campervan, motorhome, caravan or van — before you spend a euro on batteries, panels or a charger.

What it does

You enter your appliances (with their power and daily hours), your battery bank (AGM, GEL or lithium, 12 V or 24 V), your solar panels and your alternator charging. OffroadWatt then calculates, in real time, your daily consumption, your solar and alternator production, the residual deficit and your autonomy in days — all expressed in amp-hours (Ah), the way leisure batteries are actually sold in Europe.

How the numbers are calculated

The engine is deliberately transparent — the same arithmetic any installer would do by hand:

• Consumption: each appliance's watts × hours/day = watt-hours, summed, then divided by the pack voltage to give Ah/day.
• Battery: usable capacity = rated Ah × depth of discharge (50 % for lead-acid AGM/GEL, 80 % for LiFePO4).
• Solar: panel watts × peak-sun-hours for your region × MPPT efficiency, converted to Ah/day.
• Alternator: dedicated amps × driving hours × a 0.7 cable/regulator efficiency factor.

The data behind it

OffroadWatt ships with 34 real battery models (AGM, GEL and lithium, 12 V and 24 V), 41 geographic sun zones worldwide, and a community appliance catalogue that grows as people search for real components and their measured consumption. The blog documents the methodology in depth, with worked examples and comparison tables.

Why it's brand-neutral

OffroadWatt has no battery, panel or charger to sell. Recommendations are driven by your numbers, not by an affiliate quota — the opposite of a manufacturer's sizing wizard. It's built and maintained by a solo van-electrics enthusiast, and the source is public on GitHub.

Languages

The calculator and the blog are available in English, French and Spanish, with region-aware vocabulary (campervan / fourgon / autocaravana) and solar production tuned to your part of the world.