Off-Grid Cabin Solar System Calculator

Usually less than people expect. A weekend retreat running lights, a fan, and a laptop uses about 0.5 kWh per day, which needs under 200W of panels in most states. A full-time cabin with a chest freezer, well pump, and washing machine lands around 2–3 kWh per day, or roughly 500W to 1 kW of panels.

Air conditioning changes the picture: a window unit running 8 hours adds 8 kWh per day on its own and can push the array past 3 kW. Add your appliances in the calculator above for a precise number. The key driver is your daily watt-hour consumption, not the number of rooms or square footage.

48V is the right choice for most off-grid cabin systems above 2 kW. Higher voltage means lower current for the same power, which allows thinner wire over long cable runs and reduces resistive heat loss.

12V is practical only under 600W. 24V works from 600W to 2 kW. Above 2 kW, 48V is the clear winner: nearly all quality off-grid inverter-chargers are 48V, and the battery wiring is far more manageable.

Your inverter needs to handle your peak simultaneous load. Add up the watts of every appliance that might run at the same time, then multiply by 1.25 for a safety margin.

Pay attention to motor surge: well pumps, chest freezers, and washing machines draw 3–5x their rated wattage for a split second at startup. Check the inverter's surge rating alongside its continuous rating. Most quality units handle 2x continuous for a few seconds. If your well pump is 500W continuous, look for an inverter with at least 2,000W surge capacity.

Yes, but both require careful sizing. A 1/2 HP well pump draws about 500W continuous but can surge to 2,000W at startup. Size your inverter to handle the surge rating, not just the continuous watts.

A window AC at 1,000W for 8 hours adds 8 kWh to your daily load, which can roughly double panel and battery requirements for a small cabin. Add these appliances one at a time in the calculator to see the exact impact on system size and cost.

Hardware alone (panels, batteries, inverter, charge controller) typically runs $3,000–$15,000 for a DIY cabin system. The battery bank is usually 40–50% of total hardware cost. LiFePO4 batteries cost $200–$350 per kWh but last 10–15 years with minimal maintenance.

Budget another 30% above hardware for balance-of-system costs: mounting, wiring, conduit, breakers, fusing, a transfer switch, permits, and any professional labor. The cost estimate above covers hardware only.

The electrical formulas are standard engineering, the same ones professional solar designers use. The 0.8 efficiency factor accounts for panel temperature derating, MPPT losses, and wiring resistance. Accuracy depends on your inputs: use label wattages and honest daily usage hours.

Cost ranges are based on 2026 component pricing for DIY procurement and cover hardware only. Size panel and battery capacity 20% above the calculated minimum when buying equipment to account for real-world variation and future load growth.