Off-Grid Solar System Calculator
Cabin, RV, or fully off-grid home — this calculator turns your daily energy use into a complete kit spec: solar array size, panel count, battery bank, and inverter rating.
Small cabin 2–5 · tiny home 5–10 · full home 15–30.
Use your worst season if you live there year-round.
Cloudy days the battery must cover alone.
Everything that could run at once.
Solar array needed
0 kW
0 × 400 W panels
Estimates for planning only. Off-grid design involves charge controllers, wiring, and code compliance — have a professional review your final kit.
How this off-grid calculator works
Three components, three formulas. Array kW = daily kWh ÷ (sun hours × 0.78) — the array must replace a full day's use even after system losses. Battery kWh = daily kWh × days of autonomy ÷ depth of discharge — the bank carries you through cloudy stretches without dropping below a safe discharge level. Inverter W = peak simultaneous load × 1.25 — the inverter handles your worst-case moment, not your average.
Off-grid sizing should use your worst season's sun hours — a system that only works in July isn't off-grid, it's a summer toy.
Off-grid solar FAQ
How much solar do I need to go off-grid?
Daily kWh ÷ (sun hours × 0.78). A cabin using 5 kWh/day with 4 sun hours needs ~1.6 kW — four 400 W panels. A full home at 25 kWh/day needs 8 kW+, plus a large battery bank.
What are days of autonomy?
Cloudy days the battery can carry alone. Two is the common minimum for off-grid homes; RVs often accept one; critical systems use three or more. Each extra day multiplies battery cost.
What size inverter do I need off-grid?
Peak simultaneous load plus ~25% headroom for motor surges. If kettle, pump, and fridge could overlap at 3,000 W, choose a 4,000 W or larger surge-rated inverter.
Why do off-grid systems need bigger batteries than grid-tied homes?
No grid fallback: the bank must store a full day's use × days of autonomy at a safe DoD. Grid-tied batteries only bridge outages or shift peak hours, so they're a fraction of the size.