Planner · Off-grid power
Work out the battery, solar and inverter a van or cabin actually needs
Add the appliances you actually carry — fridge, fans, kettle, Starlink, heater — and get daily watt-hours, battery amp-hours for lithium and lead-acid, solar watts, inverter size and per-circuit cable guidance. Everything runs in your browser.
Appliances
0 itemsWatts and hours are nameplate figures. Adjust hours to reflect real duty cycle — e.g. a compressor fridge may run 8 h of each 24 h, not 24.
System
sizing inputsSystem diagram
live figuresDaily energy
Wh / dayAppliance detail
Wh/day per item| Appliance | W | h/day | Qty | AC/DC | Wh/day | Peak W |
|---|
Cable guidance
≤3% drop, copper| Circuit | W | A | Min mm² | AWG |
|---|
Based on one-way length 4 m (return path doubled) and 3% drop at system voltage. Check your local code before buying cable.
What to fix before you buy
How the numbers are worked out
Every figure below is arithmetic you can check by hand. Nothing is fetched from a server.
Daily energy
Per appliance Wh = W × h/day × qty. Totals split into DC
Wh and AC Wh. Inverter loss applies only to AC:
AC draw = AC Wh ÷ η and
loss = AC draw − AC Wh. Total = DC + AC draw. Average
watts = total ÷ 24.
Battery
Usable Wh = daily Wh × autonomy ÷ DoD. Ah = usable Wh ÷ system voltage. The grid shows both lithium (≈0.90 DoD) and lead-acid (0.50 DoD) so you can compare chemistry. Your own DoD setting sizes the main recommendation.
Solar & inverter
Solar array W = daily Wh ÷ (peak sun hours × derate × controller eff). After subtracting alternator Wh/day, the remainder must come from sun. Inverter continuous = AC peak × 1.25; surge = largest single surge watts × 1.5.
Cable
Current = W ÷ V. Required copper area for ≤3% drop:
A = 2·L·I·0.0178 ÷ (V·0.03) where L is one-way metres and
0.0178 Ω·mm²/m is copper resistivity. The next standard size up is
shown with its AWG equivalent.
What this is not: a planning estimate from nameplate figures; real consumption varies with duty cycle, temperature and inverter losses, and cable sizing must be checked against your local code.
Preset wattages are typical nameplate values for that class of appliance, not one vendor's spec sheet.
Questions
How much battery does a camper van need?
Add each appliance as watts multiplied by hours per day and quantity, split AC and DC. Add inverter losses to AC loads, multiply daily watt-hours by autonomy days and divide by depth of discharge and system voltage to get amp-hours.
How do I size solar for daily use?
Array watts equals daily watt-hours divided by peak sun hours times derate times controller efficiency. A derate around 0.80 covers heat, dust and wiring; an MPPT controller runs around 98% efficient.
What inverter size handles surges?
Size continuous watts as total AC peak watts times 1.25. Check the single largest surge — watts times its surge multiplier — and require surge capacity at 1.5 times that figure.
Do I need a different cable for each appliance?
Current is watts divided by voltage. Size the cable so voltage drop stays at or below 3% for the one-way run length, using copper resistivity and doubling the length for the return path, then pick the next standard cross-section.
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