What size battery do I need for off-grid power?

Add up each appliance’s watts times hours of daily use to get daily watt-hours, then divide by your battery’s usable depth of discharge (80% for LiFePO4) and multiply by the number of backup days. The SunSee calculator does this automatically.

How many solar panels do I need to recharge in one day?

Divide your daily watt-hours by your region’s peak sun hours, then divide by about 0.75 to account for real-world losses (wiring, charge controller, temperature). That gives the solar wattage needed to replace a full day of use.

What size inverter do I need?

Add the running watts of everything you might run at once, then add roughly 25% headroom. Motor and compressor loads have a surge on startup, so the calculator factors in a surge multiplier.

Is the SunSee calculator free?

Yes. It is completely free, requires no signup or email, and outputs battery, solar, and inverter specs plus matching product recommendations.

Power System Calculator

Add appliances → set conditions → get your system specs + product recommendations

Just checking one device? See runtime by appliance →

Scenario

Appliances

Settings

Results

What's your use case?

Pick a scenario — we'll pre-load relevant appliances.

Power System Calculator

What's your use case?

Camping

RV / Van Life

Home Backup

Off-Grid Cabin

Outdoor Work

Emergency Prep