Free sizing tools · no signup
Most off-grid builds fail on paper first.
Undersized battery, oversized inverter, panels that can't keep up in January. Work out the numbers here, then buy once.
Three calculators
Start with load. Everything else follows.
Every one of these takes your appliance list and returns a number you can put in a shopping basket — with the assumptions shown, so you can argue with them.
Battery bank
Daily load, days of autonomy and chemistry into a usable Ah figure. Accounts for depth of discharge and inverter losses, which is where most online calculators quietly cheat.
Open Output · watts of panelSolar array
Panel wattage for your latitude, with a separate winter figure. If you only size for the annual average you will run a generator from November to February.
Open Output · continuous & surgeInverter
Continuous rating, surge headroom for motor loads, and the DC current draw that determines your cable gauge and main fuse.
OpenWhy the numbers matter
Undersized banks die early
Pulling an AGM bank below 50% repeatedly can cost you most of its rated cycle life. The cheap battery becomes the expensive one.
Oversized inverters idle away power
A 3000W inverter left on can draw 20–30W doing nothing. Over a day that is a meaningful share of a small bank.
Annual averages hide winter
Peak sun hours in December can be a third of the July figure. Size for the season you intend to be there.
Guides
Written for people holding a crimper.
Wiring a van electrical system
Bank, charge sources, distribution and protection — in the order you should actually install them.
LiFePO4 vs AGM, honestly
Where lead acid still wins, and where the price gap has closed enough to stop arguing.
DC cable and fuse sizing
Ampacity, voltage drop over run length, and why the fuse protects the cable rather than the device.